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  1. #1
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    MP66 & Compressor Overheating



    Working on an MP66 cold plate system that the previous company walked away from. System was R12, last company put in 409. Wouldn't pull below 0 cold plate temp, cold plates freeze at -10. I put in MP66. Had high compressor outlet temps and had to run compressor superheat very low to get below -10. Just put in a liq/suc heat exchanger trying to raise comp superheat.........well it did. Up to 80 to 100 degress. Tried various evaporator superheats, no luck, still see very high comp outlet temps. Been trying various settings until outlet temp gets to 225, then shut it down to cool. Looks like I made things worse, as usual. What am I missing? Only thing I can think of it that I need an equalized TEV. Don't know what the pressure drop is across the plates but there's a fair amount of tubing in them (probably 60 ft. of 3/8). Help!!!!!

    Thanks, Kevin



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    Re: MP66 & Compressor Overheating

    Some questions Kevin: what's a MP66 cold plate system?

    Cold plates freeze at -10(°C?)So it's for a coolin application. Right?

    Had high compressor outlet temps and had to run
    compressor superheat very low to get below -10.

    How did you do this? I can't follow you. Superheat has nothing to do wit reachinhg an evaporating temperature.

    Just put in a liq/suc heat exchanger trying to raise comp superheat
    What was your intention by installing a HA?

    80 to 100 Degrees SH
    It's more like an egg boiling device.

    Isn't it normal that with high SH you will have high discharge temperatures, don't you think?

    Most probable cause: defective TEV, mositure in system, blockage in the TEV,...
    Cold plates are many times installed with a MOP TEV, so high SH at start up is then normal.
    You must give it some time.

    You said you probably need a TEV with external egalisation.
    How many plates do you have and what type of compressor?

    Try to use SI units between brackets please
    Last edited by Peter_1; 15-08-2006 at 08:16 PM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Peter,

    Thank you very much for your reply. I'm going nowhere on this and appreciate your input.

    Plates are -10F freezing point

    I had to run very low superheats to get enough ***** into the compressor to keep discharge temp below 225F so that I could run it longer than 4-5 min. When I did this, I could get the plates to cool and after a while (20-30 min) I could then increase the compressor superheat to normal values of 20-30 degress while still keeping exhaust temp below 225F. Then I put in the heat exchanger and became even dumber in the process.

    My hope on installing the heat exchanger was that with cooler liquid (about 70F versus 105F) that I could get the plates to pull down faster and that with normal superheat I sould stay under 225F. I wasn't expecting the gas temp go up 100 degrees or more. Obviously now with the heat exch., the overheated discharge is due to the high inlet temps.

    I can definitely fry eggs on the compressor if I leave it run.

    Small system, 1.5HP hermetic, three plates in series. Water cooled, 85F cooling water temp. The TEV is standard, not an MOP. Once I get the thing over the hump it starts to make more sense, it's just getting to the hump......

    Owner said that with R12, he was able to pull plates down to -15F in about 1.5 hrs. With all the mess I've made, I'm happy to see them at 0F in three+ hours

    Thoughts, I know I'm probably missing something obvious but my mind is fried from sitting around a hot compressor.

    Many thanks, Kevin

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    Re: MP66 & Compressor Overheating

    Kevin, I think I can say we have some experience with this.We're even making the plates ourselves.

    Easy, -10°F= -23°C.

    The HE isn't the cause of your problem neither the solution of it. I never used a HE in my whole career because I don't believe in it. If you look at it pure thermodynamic, it's a zero operation.

    It had worked in the past, so you must focus on something else.

    Have no experience with MP66, is this a drop-in for R12?

    On the startup, high SH is normal but the values you give, 225°F( I did the conversion myself 107°C) seems indeed too high.

    What type of valve is installed and what orifice is in it?

    I shouldn't believe what your customer is telling you, 1,5 hour is impossible. You allways have to listen what they tell you but take the some distance and try to figure out if it make sense what they tell you.

    Never believe them for 100% but their story could give you valuable information, even if your customer is not a tech.
    I don't know how long you're in the business and how much aexperience you have but that's the advice I gave my son.

    Most systems we install, also 1,5 HP hermetic and plates on -10°C(13°F which goes even much faster then your plates) takes almost 8 hours to cool down. You can calculate this yourself by calculating the latent heat of the mix in the plates.
    It will soon reach the eutectic temperature but it takes many hours to solidify the eutectic mix.

    Change your valve to a Danfoss TE 2 (an external equalization isn't needed for only 3 plates) or a similar one with same capacity, mount an orifice 1 in it, probably a 2 and replace the drier.
    I'm almost sure it will work, but give it some time (speaking in terms of some hours) to remove all the latent heat out of the mix.

    Install also a SV, electrical parallel connected with the compressor or even better, pump it down. Otherwise all the refrigerant will migrate to the plates at standstill and this is something the compressor doesn't like at all.
    Don't use also a thermostat like so many do but let it cut out on a pressostat, set at +/- 6 to 10 K below the eutectic point. Give a DP so that it starts back around the eutectic point.

    Give me some more information regarding my questions about
    MP66
    Type compressor
    Type TEV

    And now you or others have to help me :
    Is pressostat a correct English expression?
    Is it eutectic or eutectical solution?
    Is it ourself or ourselves?
    Is it external equalisation or egalisation?
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Peter,

    Wow, you're the first one I've talked with that knows cold plates.

    I can help with some of the questions:

    pressostat - Probably European, being form US, I call it a pressure switch.

    eutectic - this is definitely correct, the thermodynamic term is eutectic point.

    ourself/ourselves -- if you're talking about you individually, it's ourself, if you're talking about your company, it's ourselves.....from the wife, much better english tahn mine.....

    It's equalisation, equalzation over here.

    To the less important stuff,

    MP66 (R401B) is a low temp R12 replacement. It's a blend with 8 degree glide. Requires oil change from mineral to AB. It's the only thing out there that dosen't require POE and works for low temp applications as far as I know.

    Compressor is a Tecumseh, low temp, have to look up the model number if that's useful.

    TEV is a Sporlan GF1Z, low temp, 1 ton capacity.

    Startup superheat is around 100F. The 225F is the compressor discharge temp. which is where the first problem is. Compressor superheat really never drops much below 80F with heat exchanger. Ran it down to 10F (before I installed the heat exchanger) in order to keep discharge temp below 225F.

    I think customer was talking about average daily run times to pull the plates down, not total pull down.

    "Install SV", not sure what you mean, but there is a liquid line solenoid to stop plate flooding on turn off. System has both temperature and pressure switches, I agree on using pressure switches as you said. Not sure why there is a temperature switch also. Hasn't been an issue because I haven't gotten the plates low enough to worry about that yet.

    Installed new liquid and suction side filter driers (first thing I did on this job)

    Experience, not nearly enough, only about 5 yrs, mostly residential with a little commerical supermarket , first time working with low temps and cold plates.

    You mentioned in your first note a defective/clogged TEV. Will pull it out tomorrow and check. Just doesn't seem like there is enough refigerant flow.

    Once again, many thanks, really appreciate the help and someone who knows what they are doing!

    Kevin

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    Re: MP66 & Compressor Overheating

    HI Kevin,

    Welcome to the RE forums. I see you have already met Peter.

    Are the plates you are using made by Dole?

    Here is some information that may be worthwhile:
    http://www.doleref.com/Assets/Sales%...%20Catalog.pdf (+2 MB)

    The plate systems I remember working on were all R-12, however it did take almost all night for them to re-charge completely. Certainly not 1-2 hours.

    Peter was right on the money when he said listen to the customer, but don't believe all of it.

    The systems I worked on had normal TXV's (no MOP) but they did use a crankcase pressure regulator (CPR) valve to keep the compressor suction pressure down to a reasonable level until the plates started to cool down.

    I suspect an internally equalized TXV will work OK. The length if tubing in the plates is not too long. It just sounds like a long run.

    How warm are the plates when you try to start the refrigeration system?

    Let's start with the easy stuff before we get too excited about system problems.

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    Re: MP66 & Compressor Overheating

    Good morning Iceman,

    Thanks for the welcome. Looks like a great place, after browsing many threads, really impressed with knowledge/humor here.

    Can't tell the plate manufacturer but after looking at the Dole info I doubt if they came from Dole. Just don't look at all similar.

    Plates are typically about 10F when I start up. In the PM I'm able to run the compressor in 5 min intervals, letting things cool between runs, and get it down to around 0F so it can hold till I get back the next day.

    Getting meaningful readings in this mode is difficult as things haven't stabilized and all the readings are moving.

    Appreciate getting back to the easy stuff. Maybe you can spot something that I've obiviously missed. All I've learned dosen't seem to be working.

    Thanks, Kevin

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    Re: MP66 & Compressor Overheating

    A little more information:

    Decided to try a few things again. Here's what happened. Was able to stabilize things with the compressor exhaust temp around 216F. Saw it vary +/- a few degress as TEV cycled (I think). Read -6 psi (about -12 in Hg) for a -40F vapor temp. Plate outlet temp -30F, superheat 10F. Opened TEV one turn.....thinking this would decrease superheat a bit, raise pressures to a more normal level. Within 1 minute of doing this, exhaust temp rose quickly to 225F and heading higher. Shut system down. Plates are about 0F.

    Clogged TEV???? Pulling it now to check.

    Many thanks once again, Kevin

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    Re: MP66 & Compressor Overheating

    Just finished checking the TEV. Nothing in inlet screen to speak of. Removed TEV, heated it up some to remove any signs of moisture, reinstalled and evacuated. Restarted system, same results.

    I'm about to throw in the towel.............

    Kevin

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    Re: MP66 & Compressor Overheating

    SH seems +/- normal, what's your HP and SC?

    6 psi = +/-0,4 bar, so this seems also OK.

    Was the original pressure switch setting not set below atmospheric pressure?

    There's a chance that non condensables have entered in the system.

    225°F = +/- 108°C, far too high.

    Remove all the gas, vacuum it and look if vacuum holds, to be sure you have no leaks and refill it with a new charge.

    How I do it: fill the gas in an empty, dry and clean cylinder. While the systems vacuums for the needed time, let standstill the cylinder with the recovered gas so that the liquid gas and the non-condensables separate well.
    Take another empty cylinder and vacuum it a little bit. Release or purge the gaseous refrigerant from the first cylinder - and the non condensables) from the recovery cylinder to the second one. Most of the non-condensables are now in the second cylinder. Refill it with the recovered gas.

    Another method if you have to turn your cylinder to fill with liquid refrigerant.
    Weight the empty cylinder precisely
    Recover the whole charge again in this cylinder and weight the amount of refrigerant in the cylinder.
    Turn it upside down and let it stand there while vacuuming.
    Refill it in liquid form but let some liquid (+/- 200 gr) in the cylinder, acting as a liquid seal so that the n,non-condensables can't enter the system.

    Was this explanation clear and do other posters use a similar workmethod? Feel free to comment.

    The cylinders with a tube downwards for charging liquid while standing upright are more difficult to use because you're never sure that the tubes goes straight to the bottom of the cylinder.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    See our messages crossposted each other. Have you refilled with the original gass?
    You're sure you use the right gass?
    HP and SC are valuable readings you have to make.
    I'm doing this (temperature readings) mostly with my bare hands, especially with R-12 drop ins. Try to learn and to use this technique.
    Isn't there a possibility that the original gas filling has decomposed?
    Last edited by Peter_1; 16-08-2006 at 08:15 PM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Quote Originally Posted by Intermez
    Just finished checking the TEV. Nothing in inlet screen to speak of. Removed TEV, heated it up some to remove any signs of moisture, reinstalled and evacuated. Restarted system, same results.

    I'm about to throw in the towel.............

    Kevin
    It's not because you don't see moisture or debris that it's functioning the right way. There can also be a possibility that the gas charge of teh bulb is partially gone.

    But I think not in your case because the valve regulates for its 10K SH.

    Don't throw the towel in the ring now, these are situations you will learn the most of and especially the pride you will feel if you finally have solved the problem. And not to forget, a satisfied customer.
    This is the learning process many of us did so many years.
    You're close to solve the problem now, don' give it up now.

    Can others help in this issue?
    Last edited by Peter_1; 16-08-2006 at 08:14 PM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Has any of the components been replaced from the original installation? Do you have the same compressor, TXV, etc?

    Second point... With the exception of one post all of the data you are suppying to us is temperatures. You need both pressure and temperature to find problems.

    What is the suction pressure and discharge pressure (don't call that the exhaust pressure, you will only confuse others).

    What is the suction temperature and discharge temperature? Both of these you can find with a thermometer at the compressor service valves. About 6 inches away from the valves should be fine.

    Next question: What kind of condenser do you have? Air-cooled I suspect. Does it have any dirt in it? Look at both sides of the condenser coil. Sometimes you have to blow them out with compressed air.

    Next question: Are there any regulating valves in the suction line between the cold plates and the compressore suction service valve?

    How was the system charged with MP66? If you charged it with gas, you will have some problems. That is what Peter was describing I believe.

    What is the liquid line temperature after the receiver, or condenser?

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    Re: MP66 & Compressor Overheating

    USICeman, indeed, charegd gasseous MP66 or the original charge ahd a small leak and some of the components went out the solution.

    Indeed, a crankcase pressure regulator.

    Intermez, this isn't meant personally but so many techs forget that a system never can't be proper analysed if you don't have some basic readings: LP, HP, SC, SH, discharge temperature, liquid temperature, suction temperature. All these must fiit together and if there's one or more jumping out the row, then mostly you can better pinpoint the system.

    I wrote an article for the Belgium C&C which describes the technique of 'feeling' temperatures with your hands. It's of course written in Dutch.
    Last edited by Peter_1; 16-08-2006 at 08:38 PM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Hi Peter,

    I wrote an article for the Belgium C&C which describes the technique of 'feeling' temperatures with your hands. It's of course written in Dutch.
    This is something a lot of people never learn to develop. I learned this from my grandfather .

    Of course you do have to learn which pipes are the most likely to very hot too.

    I think you have said in the past to spit on them. It may appear to be a unsanitary service method, but it works, right?

    Once he gets use to this method, he can probably know what the problems are before the gauges are installed.

    One other question... Why is the plate temperature trying to be kept at -30F (-34.4C)? This is a lot colder than any plates I have seen or worked on. There was a mention of 12 in. Hg, which sounds very low to me.

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    Re: MP66 & Compressor Overheating

    Thanks guys for the input. I have been doing most of the things you mentioned. This answer might be long but here's all the data:

    Original installation:

    1.5 HP Tecumseh hermetic compressor
    Liquid and suction accumulators
    Water cooled condensor
    R12
    Mineral Oil
    Don't have any readings for this system. Apparently worked for years.

    2nd installation by another company.

    Hardware all the same except:
    Changed to a Sporlan GF1Z TEV, changed system to R409a
    There are no pressure regulating devices of any sort in the system other than the TEV.
    They never got it to work.

    3rd System

    This is where I came on the scene. From all I've read and input from others, all said that R409 wouldn't get below 0F very effeciently. All suggested going to R401B (MP66) because of -10F freezing point of plates. This necessitates at least -20 or -25F evaporation temps for good heat transfer between the refrigerant and brine in the plates.

    Here's what I did.

    Verified that the Sporlan TEV currently installed was
    acceptable for R401B. Recovered system completely.
    Cleaned system with solvent, removed as much oil as I could from the compressor. (I didn't want to assume that the previous company had correctly changed from mineral oil to AB.) Added AB oil, evacuated and then charged system with R401B.

    Here are the readings I had at the time:
    HP 160psi
    Discharge temp climbed to 225F within 5min of startup.
    Evaporator pressures and temps were continuously decreasing as system was still pulling down. Evaporator pressures went form +10psi down to at most -11 in Hg. The low end pressure varied bacause I was trying various superheat settings to keep the discharge temperature down low enough to keep the system running so I could get some stable readings as a starting point. (Assuming more ***** flow, lower superheats would cause more compressor cooling). During this process I found that if I set the superheat very low, and the corresponding compressor superheat low (it ran about 10F) that there was enough cool ***** getting to the compressor that I could keep it running long enough so that discharge temps would come down to aroun 200F. At that point I would try increasing superheat at the evaporator to around 8 degress and the discharge temp again would starting to rise to 225F+.

    During all this I was running SC pressures from +4 psi down to -8in Hg. Compressor inlet temps of course varied with the particular setting I was trying, but were around 0F plus/minus 15 degrees, Whatever I tried couldn't find a balance.

    2nd step:

    For some reason I thought I'd install a liq/suc heat exchanger, hoping that the cooler liquid temps entering the evaporator would help things pull down quicker, allowing the system to stabilize faster. Didn't work because with the heat exchanger, compressor inlet temps rose to 60F to 80F and exhaust temp were obviously high. When I installed the heat exchanger, recovered the R401 and put in a completely new charge.

    3rd Step

    Checked TEV as best I could. First heated TEV with hair dryer to see if I could unfreeze any possible moisture. No effect. Removed TEV to check inlet screen. Nothing found. Checked TEV operation with 100 psi nitrogen, bulb both cold and hot. TEV seemed to function. Replaced TEV. Evacuated and started system; here's the reading I got:

    RUN 1
    Sc (evaporator outlet pressure) -4 in Hg
    Evaporator discharge temp -19F
    Plate temperature -2F
    Superheat 8F by my caculations
    HP 162 psi
    Compressor suction temp 70F
    Discharge temp 225F
    Condensor Refrigerant Out Temp 105F
    Condensor cooling water inlet temp 85F
    Condensor cooling water outlet temp 94F

    These readings were after 7 min of run time. Compressor had been cooled to ambient (90F) before starting. Plate temperature dropped 2F during the run.

    RUN 2

    Next tried increasing superheat, 1 turn in on TEV

    SC pressure -11 in HG
    Evaporator discharge temp -24
    Superheat around 16F
    Everything else about the same, run time before reaching 225F was 12 min. HP 160psi, compressor suction temp 68F.

    RUN 3

    Just ran it one last time after colling the compressor. MAJOR CHANGE: Reset TEV to where it was for RUN 1 above. Immediately on startup compressor suction temp dropped quickly to around 30F, gradually down to 8F and then back up to 38F. Forst building on compressor suction valve, then disappearing. Did not hear any sign of liquid slugging (due to accumulator I would assume) Compressor discharge temp rose to 217F down to 200F and then back up to 225F. Run time 23 mins.
    At 214F discharge temp the readings were:

    Evaporator discharge pressure -2 in Hg
    Evaporator discharge temp -28F
    Superheat 0 to slightly negative
    Compressor suction temp 38F
    HP 155psi
    Condensor discharge temp 100F

    I added two turns of supreheat (should be 4 or 5F increase). By the time I got to the compressor to look at the discahrge temp, it had risen to 224.3 and was climbing quickly.

    Let compressor cool, started another run, and once again saw 80F compressor inlet temps. Shut things down and went home.

    Question: What would have caused such a drastic change in compressor inlet temps?

    Sorry this took so long, hope there is enough pressure data. Will be more careful in the future to write down everything! Hope I answered all the questions, mind is sort of fried at the moment.

    THANKS, Kevin

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    Re: MP66 & Compressor Overheating

    First of all here is a link to the pressure/temperature tables for this refrigerant (and others).

    http://refrigerants.dupont.com/Suva/...pdf/k10909.pdf

    Let's start with this example...

    RUN 1
    Sc (evaporator outlet pressure) -4 in Hg
    Evaporator discharge temp -19F
    Plate temperature -2F
    Superheat 8F by my calculations
    HP 162 psi
    Compressor suction temp 70F
    Discharge temp 225F
    Condenser Refrigerant Out Temp 105F
    Condenser cooling water inlet temp 85F
    Condenser cooling water outlet temp 94F
    First some questions... What is Sc?

    If the evaporator outlet pressure is 4 in.Hg (you do not have to use the minus symbol here, the vacuum already shows the pressure is negative)

    4.2 in.Hg = -26F according to the table posted above

    If the temperature of the suction line leaving the plate is -19F (you called it evaporator discharge).

    -19F minus -26F = 7 degrees of evaporator superheat. That's not too bad if your numbers are correct.

    Now, your suction temperature at the compressor is 70F. If we take the 70F suction temperature minus the -19F, you have over 89 degrees of superheat added to the evaporator superheat of 7 degrees. That's 96 degrees of total superheat at the compressor. That's enough right there to make the compressor very hot.

    Looking at a pressure/enthalpy diagram that would put your discharge temperature around 250F or so, which means you are about right were I would expect with this much suction superheat.

    The discharge pressure and liquid temperature leaving the condenser look about right. As does the condenser water temperature range. In other words, these look reasonable.

    It would be nice to know the suction pressure now. The suction pressure SHOULD be close the evaporator outlet pressure if nothing else is wrong. A little lower, but not much.

    At this point without the compressor suction pressure, I have to guess...

    Somewhere between the outlet of the evaporator plate and the compressor suction service valve something is adding about 90 degrees worth of superheat to the suction line.

    Or, something is causing an extreme pressure drop in the suction line in this area. Very high pressure losses in the suction line will appear to be only superheat. But since we don't have the suction pressure, well...

    If the suction line is not crimped, or full of solder, then you more than likely have something adding a lot of heat to the suction line.

    I suppose the liquid line could be crimped or blocked to some extent, which could cause the liquid to flash off before it enters the TXV. Does the TXV sound like it is hissing, or gurgling a little? Is the TXV cool or warm?

    What are the motor amps? Are they close to something that agrees with the compressor nameplate full load amps (FLA)?

    You have an interesting problem that's for sure.

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    Re: MP66 & Compressor Overheating

    Iceman,

    Thanks again. Someone, perhaps Peter used the term SC, I took this to mean suction. Anyway that's what I meant.

    I measured the pressure drop from the evaporator outlet to the compressor suction port a few times. The most I have ever seen is 2psi.

    The superheat added to the suction line is coming from the heat exchanger. However, if you got far enough into my novel, what I don't understand is the one run (think I called it Run 3) where the suction temperature dropped to 30F quickly after start up, then over the next 5 min. down to 8F and then gradually back up to 40F. This is with the heat exchanger in place. Unfortunately did not have a guage at the compressor to read the pressure there at the time. With the next start up of the system, the suction temperature was back up to the 70 to 80F range. I'll measure the pressures at both the evaporator and suction port at the same time tomorrow.

    I hear no sign of any gas passing through the TEV, no hissing, gurgling, etc. Amps drawn by the compressor start up near FLA of 14, gradually drop off to below 9 amps. Sorry about the -4 in Hg. My background is electrical, I add a - sign to anything that goes below zero.

    By the way, before I put the heat exchanger in the system, the suction temps were lower but still had high discharge temps.

    Keeping the towel handy, but like you said, I want to somehow solve this, and once again learn how much I don't understand..

    Kevin

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    Re: MP66 & Compressor Overheating

    I'm thinking now on something: we had a service-call 2weeks ago on a eutectic plate.
    The fed-troughs were cracked.
    The explanation will be too long for the moment now but the fed-trough exploded while I was soldering it. I thought that moment I lost my hearing.

    The tube is a 1/2", fed trough a 5/8 to prevent cutting on the sharp edges of the stainless steel plates. We always make stainless steel plates.

    You can see on the pictures that the outlet of the plate that the inner pipe is almost completely flat squeezed.
    Before I soldered it and before it exploded, both tubes looked similar, so it was squeezed inside the 5/8".

    Happy now I took a picture of this 'stupidity'
    And perhaps strange to say but if it hadn't exploded, I never should have seen this fault.

    I haven't checked in the pressure/enthalpy chart if your pressing/temperature readings are correct and correspond with each other but USIceman did it already, so his conclusions will be right: a blockage.

    Solder a schradervalve between plate 1 and 2 and between 2 and 3. If everything is OK, then all readings, including the suction pressure at the compressor should be the same.
    You then better can locate the blockage in your system.
    Attached Images Attached Images
    Last edited by Peter_1; 17-08-2006 at 11:33 AM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Good Morning Peter,

    That looks like it was quite an explosion. I take it you fill the plates with hydrogen before soldering.

    Any idea what happened to cause it to blow like that?

    I'll put the Schrader valves in today. Unfortunately there's no way to get one in right at the TEV outlet, but can get at the other two points.

    What do you think could be causing a blockage if it's not something like a crushed tube? I would think it would take a lot to block a 3/8" tube.

    Thanks!, Kevin

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    Re: MP66 & Compressor Overheating

    What do you think could be causing a blockage if it's not something like a crushed tube? I would think it would take a lot to block a 3/8" tube.
    Well, freezing water has squeezed my tube of 1/2.

    Could also be a foreign object of the previous tech.

    Found once - +/- 10 years ago - a small piece of cloth in the outlet of a receiver of a milktank. It must been there since fabrication in factory.
    You should have seen the farmer's face when I grinded open the reservoir. He couldn't believe that I could know that something was inside the reservoir.

    The explosion I had was trapped water between the 1/2" and 5/8 " tube which made very fast steam while I was heating it. My wife was inside the home and she ran to me when she heard the explosion. I was soldering it in place in a small closet.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Well it seems to me that the guys who worked on this before did something that really messed this up.

    Quote Originally Posted by Peter
    Could also be a foreign object of the previous tech.
    That is what I'm thinking. Unless, if you can make sure the suction line pressure loss is no more than 2 psi from any plate outlet connection back to the compressor.

    I have trouble believing the suction line heat exchanger is adding almost 90 degrees of superheat with a liquid line temperature of only +/- 105F (40.5C). Usually you only find about 10-20 degrees of superheating, and that is high, in my opinion.

    On the heat exchanger installation I have a question. There should be four connection on this. Two are for the suction lines; one inlet & one outlet.
    The other two lines are for the liquid line; again, one inlet & one outlet.

    Are you sure the two smaller connections are connected to the liquid line? (the small line coming out of the condenser. You may have a receiver, so the two connections should be in series with this line, after the receiver.)

    You did not by any chance connect the discharge into these two connections did you? To get that much superheat (+/-90 degrees) this is about the only way I can see this happening.

    Either that, or someone installed a hot gas bypass for some strange reason???

    Without being able to see anything we have to go on your descriptions and the data you provide.

    You mention the suction temperature starts normal in some cases then quickly rises. The plates could hold enough residual refrigerant to refrigerate normally for a short while. This would quickly evaporate when the compressor is running, and then the high temp's could start.

    Quote Originally Posted by Intermez
    I hear no sign of any gas passing through the TEV, no hissing, gurgling, etc
    Take a long screw driver and place the metal end on the TXV. Put your ear on the plastic handle. Instant stethoscope! You should be able to hear something.

    Quote Originally Posted by Intermez
    I take it you fill the plates with hydrogen before soldering.
    God forbid you should do something like this. That would be an explosion you would not walk away from.

    Use free-flowing nitrogen, nothing else. The nitrogen has to flow in and out of the system in a completely unrestrained manner.

    Quote Originally Posted by Peter
    My wife was inside the home and she ran to me when she heard the explosion.
    Peter, she did not drop any of her good tea cups did she?

    Restrictions come from funny places... I have heard about about a lunch box, a piece of wood, and a bag of bolts being inside of a large suction line in an ammonia system. Strange things happen.

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    Re: MP66 & Compressor Overheating

    Thanks guys,

    Finally convinced the customer that I couldn't keep on working on this thing without emptying it. He very reluctantly agreed. Now in the process of deforsting the plates. Will add Schraders for better measurements. While things are defrosted, any recommendations on flushing solvents? I've only used a liquid type followed by nitrogen. Want to do a very thorough job before I put things back together.

    Heat exchanger was installed correctly. Might put a sight glass directly before the evaporator temporarily to look for any gas bubbles. Will also do the screwdriver check. There is no hot gas bypass valve installed. Probably won't have any news tomorrow, unless I find a mouse or the like in the suction line.

    Kevin

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    Re: MP66 & Compressor Overheating

    Why are you trying to flush the system? That could create more problems than currently exist.

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    Re: MP66 & Compressor Overheating

    Kevin,

    Perhaps not such a bad idea that you print out this whole thread - edit it perhaps a little bit - and let it show to your customer.

    He will then see that you've taken a lot of work aside the work he saw to solve his problem.

    And also to let him know that a lot of other techs worldwide have helped you and him.
    He perhaps will realise that the problem was not that easy and that the reason for the problem was already in the system when he called you.

    If you find a mice, I want a picture of it...in close-up.

    But think also once on the restriction I gave you on the picture.

    If you're self-employed, then you can make an arrangement and say that he only has to pay some hours but not everything.

    I should not flush it like USICeman suggested - a too time-consuming job and too expensive to perform - just blow it through with dry nitrogen.
    The main purpose now is finding a restriction.
    And if you find something, don't remove it before you have it shown to your customer so that he's convicned that all your work was needed to solve the problem .
    Last edited by Peter_1; 17-08-2006 at 05:04 PM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Quote Originally Posted by US Iceman
    First some questions... What is Sc?
    I used it for SubCool
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Quote Originally Posted by Peter
    I used it for SubCool
    Stupid me, I should have realized this is what you meant. When I saw it with the suction pressure in his post, I did not think about that.

    I'll try not to let it happen again...

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    Re: MP66 & Compressor Overheating

    Peter and Iceman,

    Will take your suggestions and back off on doing a flush. Will just use nitrogen.

    Definitely like the idea of printing this whole thing out and giving it to the customer. You're right, I think he would be impressed with the high quality support that's out there and the thought and time given to this whole mess.

    Hopefully will have some good news tomorrow. Will definitely be looking for wildlife in the suction line or around all the welds looking for explosive crimping of the lines. Couldn't beleive how long (9 hours) it took to get those plates above freezing. Eutectic cold plates are impressive.

    Kevin

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    Re: MP66 & Compressor Overheating

    Quote Originally Posted by US Iceman
    Now, your suction temperature at the compressor is 70F. If we take the 70F suction temperature minus the -19F, you have over 89 degrees of superheat added to the evaporator superheat of 7 degrees. That's 96 degrees of total superheat at the compressor
    According to this statement, the restriction must be in the last piece between last plate and compressor (perhaps the liquid separator) and it all depends on the figures you've given are correct and we interpreted those the right way.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Peter,

    I understand what you mean. When I'm done with the plates will look again between the plates and the suction port.

    I suspect though that there's a blockage in the plates. This could still account for the readings. How's this for a theory: Blockage in the plates, ***** flow very low. TEV able to set to correct superheat eventhough the flow is low. Since flow is low, heat picked up from heat exchanger & 30ft. or more of suction line, dryer, and receiver is able to raise the temp of the small amount of ***** in the line between the plates and suction port. Does this make sense? Only way to tell I guess, as was mentioned before, is various pressure measurements along the suction side.


    Kevin

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    Re: MP66 & Compressor Overheating

    Quote Originally Posted by Intermez
    This could still account for the readings. How's this for a theory: Blockage in the plates, ***** flow very low. TEV able to set to correct superheat eventhough the flow is low. Since flow is low, heat picked up from heat exchanger & 30ft. or more of suction line, dryer, and receiver is able to raise the temp of the small amount of ***** in the line between the plates and suction port. Does this make sense?
    Your way of thinking is correct Kevin.
    Let us surely know what you've found or if you need more information.
    Take your digital camera with you if you have one. Many can learn from this.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Low mass flow in the suction line could cause this. That is one way of explaining why the heat exchanger is adding so much heat to the suciotn gas.

    I want to ask a "stupid question". Do the plates have individual expansion valves (one for each plate) or is one TXV feeding multiple plates?

    If one TXV is feeding multiple plates, what the refrigerant distributor look like?

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    Re: MP66 & Compressor Overheating

    US Iceman, many of these systems are simply connected in line.
    We had once a van with +/- 7 plates in line.

    There's not that much copper in 1 plate.

    There are some advantages of this is if you connect them in line:

    1. You don't have to take care of making that every plate has the same pressure drop and that each plate is fed the same way
    2. Less expensive then any other system
    3. Only the last plate has to make the needed superheat. When each plate should have his own TEV, each plate need a certain unused section for superheating. So the plates are better cooled, more uniform.

    Disadvantage: if a TEV brakes, then the whole system will shut down on LP. But this happens very seldom.

    We even connected them in line through plates with a different eutectic solution (plates in the mussels stroage must have an eutectic point of -5°C, counter at -2°C to avoid freezing of the fish on the ice but making that the ice doesn't move while driving the van, the ice storage is kep at -8°C or -10°C,...).
    While pulling all the plates below their own eutetctic point (we cut it out on LP on a corresponding temperature below the lowest eutectic point in the system), the plates with the highest freezing point where frozen a little bit to deep but as soon teh compressor is shut down, they fast rise to their eutectic point and stay their while melting.

    But this did you know already, it's only shearing my experience with those just joined our métier like the French say.
    Last edited by Peter_1; 19-08-2006 at 09:56 AM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Peter,

    This is a really good discussion on system troubleshooting and system operation.

    I hope the young guys are reading this.

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    Re: MP66 & Compressor Overheating

    And that they understand the logic behind all this.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Good morning guys,

    Well you were both right and the readings as well. No blockage in the plates. Disconnected each one separately, blew them out in both directions, seemed absolutely clear and only thing I got out was a few drops of oil. Now on to the rest of the suction side.

    The three plates are connected in series with one TEV.

    I did not mention previously, but part of my job was to separate the freezer and refrigerator sections and to install a second compressor for the refrigerator.

    When I got on the job the system had the one 1.5HP compressor feeding the three freezer plates with one TEV, paralled with a second TEV feeding two refrigerator plates. Put in a second .5HP compressor and separated the refrigerator plates from the 1.5HP system. The new refrigerator system is running flawlessly.

    The freezer problem was there with both the freezer and refrigerator plates paralled on the 1.5HP compressor. Verified this before I did anything by disabling the liquid line solenoid going to the refrigerator TEV.

    Will get back with some good new today, I hope.

    Kevin

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    Re: MP66 & Compressor Overheating

    Kevin,

    Where were we both right regarding the readings?

    If I understand you correct, there was no blockage at all in the plates?

    But you said that the problemwas there when 5 (3 freezer and 2 cold room plates) were connected together. Is the problem then gone now?

    I think you have to look in the piece between last plate and compressor.
    Is liquid separator the original one? If newly installed, it perhaps was fit the wrong way (in/out and out/in)?

    Important readings you have to make for us when system runs for an hour - don't look at the discharge temperatures and let it run that way - so that it is stabilised a little bit: temperature at outlet last plate, temperature in and out HE, temperature in and out accumulator and temperature and pressure at the inlet service valve on the compressor.

    Is the 1.5 HP compressor a LP one or a HP one?
    I suppose a LP because your current is max on startup and compressor goes beyond - temporarely - its limits.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Peter,

    Both you and Iceman indicated that with the superheat readings I was getting that the blockage was not in the plates, but likely further on.

    The plates did not appear blocked. Had full nitrogen flow in each plate, both directions. Put a temporary valve at the outlet side of each plate to build the internal pressure up to about 20psi, opened the valve quickly to release pressure. Pressure dropped immediately. Don't know what else to do to check for plate blockage.

    The problem with the freezer is not gone. It was there in the beginning with the five plates, and is still there now with just the 3 freezer plates.

    Unfortunately did not take many measurements (dumb on my part) before separating freezer and refrigerator. Customer says that now with separate refrigeration compressor, the refrigerator plates are pulling down in about half the time.

    The liquid separator was in place. Will be checking for blockage, other problems downstream of the cold plates today. Will try to verify that the liquid separator is installed correctly. According to the compressor serial number it is a low temperature unit. Will take all the readings you suggest and anything else I can.

    Off to work....,

    Kevin

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    Re: MP66 & Compressor Overheating

    Forgot the most important question, is the anyway to check the suction accumulator, liquid separator for correction installation other than unbrazing it? I'm assuming that it won't be labeled, in and out, as life is never simple.

    Kevin

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    Re: MP66 & Compressor Overheating

    Don't unbraze it, there mostly a stamped in and out
    label on the accumulator.

    Well, in fact blowing through is only to clean the system.
    But you still can have a restriction, even when you have a flow through the plates.
    A capillary tube is a big restriction and you stll have flow.
    You can see on the pictures I posted the restriction but there's still a flow possible.

    Soldering schradervalves and measuring pressure gives much more reliable information.

    Therefore, the temperature readings I mentioned are important measurements you have to take.

    And pressure readings on the different sections are then the second most important readings.

    These are not the easy jobs but you can prove now that you know your job.

    I haven't re-read all the posts of this thread but where have you measured the suction pressure?
    I ask you this because if you should have taken it somewhere on the low pressure side of the compressor body and not on the service valve itself, then you also can have a restriction in the mesh filter installed inside the service valve (or in the service valve itself)
    But no, you have a hermetic compressor which has no mesh on the inlet but there's still the servicevalve. But it's good to know that this could have been also a possible restriction.

    To look for a restriction in the accumulator: you need to solder a servicevalve at the entrance of it and compare this pressure against the pressure at the service valve on the compressor.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Quote Originally Posted by US Iceman
    Now, your suction temperature at the compressor is 70F. If we take the 70F suction temperature minus the -19F, you have over 89 degrees of superheat added to the evaporator superheat of 7 degrees. That's 96 degrees of total superheat at the compressor. That's enough right there to make the compressor very hot.

    It would be nice to know the suction pressure now. The suction pressure SHOULD be close the evaporator outlet pressure if nothing else is wrong. A little lower, but not much.
    I quoted US Iceman because his comment is very important because we rely on your measurements and we develop a theory, a possible cause based on this figures you give us.
    It's therefore very important that we understand each other very well and that you corretc us eventually if we say something wrong or different from what you have measured.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Quote Originally Posted by Intermez
    The problem with the freezer is not gone. It was there in the beginning with the five plates, and is still there now with just the 3 freezer plates.
    Now we know something new! The problem was not probably related to the plates, but essentially the refrigeration system that the five plates were originally connected to.

    Since two plates are now on a separate refrigeration system and working fine, the problem seems more associated to the actual refrigeration system used for the freezer plates.

    It the problem is not a "mouse", I bet it is something left there from the previous service tech. Rubber or plastic plugs that may have been left in something and partially melted when brazing was done.

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    Re: MP66 & Compressor Overheating

    Quote Originally Posted by US Iceman
    Rubber or plastic plugs that may have been left in something and partially melted when brazing was done.
    This is something happened by myself.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Here's what I did yesterday. Didn't stay too long as it was on my own time. After reading all of your comments and thinking about it for a while, I guess the only way to determine if there is a blockage between the plate outlet and the suction port is to make simultaneous pressure measurents at the two points.

    My assumption is that during startup with a cool compressor, is this is when the flow rates through the suction side are the greatest. I first took simultaneous measurments between the inlet side of the dryer (service port already there) and the suction port. The liquid accumulator is between these two points. I also opened the TEV wide open to get the greatest flow rates that I could (higher flow should mean higher pressure drops). I saw only 1 to 1.5 psi drop from the dryer inlet to the suction port. I did this for about 5 minutes, stopping again when the outlet temp reached 225F. My conclusion no blockage in dryer or accumulator. Do you guys agree with this?

    Next I did simultaneous pressuren measurements between the plate outlet and the suction port. TEV wide open. Here's the series of measurments as the system started to pull down, again over about a 5 min. period.

    EVAP Suction
    Out Port
    Press. Press.

    15 16
    13.5 15
    13 14
    11 12
    10 11
    9 10
    8.5 9.5

    All readings in PSI. Sopped again when discharge temp reached 225F. ( Don't like the idea of just letting the system run to let it stabalize, ignoring discharge temp as Peter suggested. From everything so far it think I'd fry the compressor because of very low ***** flow). Suction port temps were high starting around 88F dropping to 81F during the above. Conclusion, no blockage between plate outlet and suction port??

    This is all I had time to do, will continue with your suggestions on Monday, back through the plates to the TEV. Will also try to take all the measurements suggested.

    Many thanks, Kevin

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    Re: MP66 & Compressor Overheating

    For some reason the table of pressure measurements and the headings for them didn't come out correctly on the post. The first column of numbers, starting at 15 and dropping to 8.5, are the suction port pressures. The numbers immediately to their right, starting at 16, dropping to 9.5, are the plate outlet temps.

    Kevin

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    Re: MP66 & Compressor Overheating

    D****, previous post, not plate outlet temps., plate outlet pressures!

    I need to relax!

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    Re: MP66 & Compressor Overheating

    Quote Originally Posted by Intermez
    I also opened the TEV wide open to get the greatest flow rates that I could...
    If I can make a suggestion... Do not adjust the TXV everytime you do something, please. Just because it has an adjustment stem on it does not mean turn the stem.

    This is a very common mistake that people continue to make. They assume if the system is not cooling properly, it either has to be low on refrigerant or the TXV needs to be adjusted. The TXV should be adjusted at full load at normal operating conditions. Once the superheat is reasonable, Leave the valve alone.

    I don't seem to remember any mention of a suction line filter drier before. What exactly do you have installed in the suction line between the three remaining plates and the compressor suction service valve?

    Right now I'm counting a; suction filter drier, an accumulator, and a liquid/suction heat exchanger. Is there anything else?

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    Re: MP66 & Compressor Overheating

    Iceman,

    I agree on adjusting the TEV. It is the last thing usually touch. Problem is this system is not operating normally and there's no way to adjust the superheat correctly with what appears to be low ***** flow.

    Yes, there are three things between in the suction line after the plate outlet. Heat exchanger, filter-dryer, accumulator, in that order. The filter-dryer was only mentioned early on. I said that after I first tried to get the system going unsuccesfully the first things I changed were the liquid line and suction line filter driers.

    THanks, Kevin

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    Re: MP66 & Compressor Overheating

    Just reading your post before I go to sleep (11:15 PM) and coming back from helping my wife. It was very busy today
    I thought the same about the suction drier. You didn't speak about that before.
    A suction drier is something that blocks sometimes, reason why they install 2 measuring points on it.

    If it's a suction drier, in fact a filter, then there are normally 2 measuring points. I suppose tehre is no pressure drop over these 2 points.

    Can you make pictures of the complete setup?

    You will need to make temperature measurements at the inlet and outlet of each component, starting at the TEV inlet.
    Somewhere, there must be a sudden temperature rise, otherwise there was something wrong explained in a previous post or we understood it wrong.

    I've seen compressors running at more then 225°F for quit some time (in terms of days)
    So don't be afraid to let it run for some longer time then you do now.
    Otherwise, you never can measure temperatures, it need some time to stabilise.

    Perhaps a little schematic with every component on it and the temperatures you have measured. Try also to measure pressure on every point where you can measure it.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: MP66 & Compressor Overheating

    Quote Originally Posted by Peter
    I've seen compressors running at more then 225°F for quit some time (in terms of days)
    So don't be afraid to let it run for some longer time then you do now.
    I agree with Peter. 225°F is getting warm, but not too bad. Now if the temperature was reaching 270-300°F then I would start to be concerned.

    Quote Originally Posted by Peter
    You will need to make temperature measurements at the inlet and outlet of each component, starting at the TEV inlet.
    Kevin, this is absolutely critical information to have for trouble-shooting purposes.

    If you mentioned the suction filter drier before, I may have missed it or forgotten it during the on-going discussion. Sorry about that.

    If the suction pressure loss is not to excessive, then we have to start looking at other things as well. It would be nice to have the respective pressures and temperatures at each component (inlet & outlet). This allows us to examine each component for relative performance we might expect to see.

    Quote Originally Posted by Peter
    Somewhere, there must be a sudden temperature rise,...
    If the pressure loss is minimal, then I think this is the next area we have to investigate. The data will tell us which direction to look at closer.

    Have you performed a pump down test of the compressor yet?

    This is pretty simple. Jump out or bypass the low-pressure switch. Attach your compound gauge to the suction valve port on the compressor. Now close the suction valve all of the way, so that it closes off the suction line to the compressor.

    The compressor should pump down into a decent vacuum within a minute or so. Say 25 in.Hg. Shut the compressor off.

    If the suction valves in the compressor are OK, the suction pressure decreases fairly rapidly. If it takes quite a while to pull down the suction pressure in the compressor, the compressor pumping capacity may be in error (leaking rings or suction valves).

    If the suction pressure increases very rapidly, the discharge valves are broken. If this pressure rise occurs after the compressor shuts off, you might hear a "hissing" sound. That's the discharge gas equalizing back to the suction pressure.

    This is a very easy check to make as it only takes a few minutes.

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