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  1. #1
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    404a high pressure?



    what would you consider a "too high" pressure for a medium temp unit using 404a?
    the pressures im working with are 65psig and 325psig with an ambient temp of 70f. the liquid line is hot (around 115f), the superheat is a tad under 30 but the unit is still coming down to temp.
    i built this cooler (a small, glass door wine cooler) from scratch and it has a new condensing unit (404a, med temp 1/4 hp) and im just not sure if i got the charge right.
    i discovered a small leak at one of my flare fittings and repaired that then this morning i pumped it down and pulled a 200 micron vacuum and refilled it with 10 oz of liquid. i slowly brought the charge up by 1/2 oz at a time up to 12.5 oz. them air temp at the evap coil was coming down slowly (46f) last i checked.
    this box is less than 20 cubic feet and i think the temp should be dropping alot faster considering the size of the condensing unit.
    also,,, there is a new txv and drier installed.
    any suggestions will be appreciated,
    thanks,
    mike



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    Re: 404a high pressure?

    It isn't about pressures, it is about temperatures.

    For starters, we need to convert the pressures to temperatures using a P/T chart.

    65psi = 26F Saturated suction temperature (SST)

    325psi = 123F Saturated condensing temperature (SCT)

    123F saturated condensing temp minus 70F ambient temp gives us a condenser TD of 53F. This is excessive and tells us that the condenser cannot handle the load. We need to find out why.

    Measure the temperature of the air entering the condenser and the temperature of the air leaving the condenser, then subtract entering air temp from leaving air temp. The result is the condenser delta-T aka dT. If the dT is more than 30F, then the airflow through the condenser is insufficient.

    If the airflow is sufficient, subtract the liquid line temp (near the condensing unit) from the SCT. The result is the condenser outlet subcooling. If the subcooling is more than 15F, there is too much refrigerant in the high side of the system, backing liquid up into the condenser, reducing its ability to reject heat.

    Your current numbers show subcooling of 123F - 115F = 8F. This is far from excessive, but we should always check dT and correct any airflow problems before checking subcooling. Airflow can and will effect subcooling.

    Let us know what you find, each step of the way.
    Last edited by Gary; 29-11-2007 at 08:28 PM.

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    Re: 404a high pressure?

    gary,, thank you for your quick reply,,,

    heres the skinny,,, about an hour ago,, i went down to check on the progress and the box temp was at 44.7f and the pressures were 57 and 300. so i added 1.2 oz of liquid (bringing me up to 13.7 oz) and that brought the high side up to 325 again and the box temp started to drop some more.
    after i read your post,, i went back down to get the temps you asked for and here is what i found.
    box temp 42f
    suction line temp 47.4f
    air going into the condenser 91.1f
    air leaving condenser 99.6
    pressures at 56 and 325 psig
    i honestly feel that i could add another ounce, but im not used to seeing such high head pressures (im not used to seeing ANY pressures as i am still new to this trade).
    admittedly, i could use some cooler air entering the condenser coil. this unit is in a box with one side open to the air and a hole (approx 12"x12") on the other side for air to enter the condenser coil. as i mentioned earlier,, its a brand new unit (new old stock) and the cond coil is shiny new and nothing seems too hot to touch,
    and the superheat is still around 27.
    again,, many thanks for your time,
    mike

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    Re: 404a high pressure?

    Quote Originally Posted by flyboy3b View Post
    and the superheat is still around 27.
    again,, many thanks for your time,
    mike
    Have you put a liquid sight glass in the line before the TEV (TXV).
    If you have charge the system till it clears.

    taz.

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    Re: 404a high pressure?

    123F SCT minus 91F air in = 32F condenser TD, which indicates heavy load, but not excessive.

    56psi = 20F

    42F air in minus 20F SST = 22F evaporator TD, again heavy load but not excessive. With heavy load comes high superheat, as we saw in your other thread.

    100F air out minus 91F air in = 9F condenser dT, indicating excellent airflow.

    Similar air in and air out measurements on the evaporator would give us the evap dT, indicating evap airflow, although the heavy evap load says that the airflow is probably sufficient.

    That brings us to the condenser outlet subcooling (SCT minus liquid line temp) and the evaporator outlet superheat (suction line temp minus SST).

    If the condenser outlet subcooling is above 15F, you have added too much refrigerant.
    Last edited by Gary; 29-11-2007 at 10:28 PM.

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    Re: 404a high pressure?

    Note: The difference between liquid line temperature and air out temperature is the condenser approach. Given sufficient airflow and normal subcooling, high condenser approach would indicate a thin insulative coating on the condenser tubes, generally resulting from carbon deposits in high (automotive) traffic areas accumulating over long periods of time. But this being a new system, we can safely ignore the condenser approach temp.

    Similarly, evaporator approach can indicate coating of the evaporator tubes, such as oil coating the inside of the tubes caused by oil logging.
    Last edited by Gary; 30-11-2007 at 12:42 AM.

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    Re: 404a high pressure?

    gary, thanks again, i will watch it over the next day or two and see how it does. at nighttime,,, the bartenders are in and out fairly often, so it will have a hard time maintaining temp, but by morning, it should be stableized and i will check it then.
    in the meantime,, i will see what i can do about getting some cooler air across the condenser coil.
    taz,,, i appreciate the help, but the last system i worked on had a site glass and when i found (what i thought) were the optimal settings for that machine, there were bubbles in the glass.
    thanks,
    mike

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    Re: 404a high pressure?

    By definition, if the superheat is right (at design room temp), you have enough refrigerant in the system to do the job. However, solid liquid entering the TXV will help to prolong its life.

    Therefore, when everything else is right, it is a good idea to slowly add a small surplus of refrigerant until the sight glass clears or the subcooling is 15F, whichever comes first. This is the optimum charge.

    The manufacturer's recommended charge gives us a quick easy way to charge the system close to optimum, which is an important consideration when you are charging the customer for your time. It is "close to optimum" because just as identical twins have subtle differences, no two systems are truly identical, much less hundreds of identical systems coming off an assembly line.
    Last edited by Gary; 30-11-2007 at 12:51 AM.

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    Re: 404a high pressure?

    Liquid line seems a bit hot and the head pressure seems a high for ambient, as gary said above you need to use the pt chart to determine what the no normal pressures are, I have always used a simple formula that calculates normal or close to normal high side pressure.

    Most condensors operate at a close to estimated temperature of 30 degrees over ambient. So if we know what are ambient is and add 30 degrees to it we can safely estimate, by this simple formula

    70 degree ambient +30 degrees= 100 degreesF
    100 degrees f for R-404a on a pt chart= 235psi

    Normal estimated press is 235 +/- 25 psi

    The normal head pressure should be between 210-260 psi. and you are at 325.

    I think we have definetly determined your high side pressure is above normal.

    Lets take a look at the suction pressure similiar as above excecpt normal operating sytems have an average coil temp of 15 degrees f below temp controlled area.

    I believe you said return air temp of 42 degrees f.

    take 42 degrees subtract 15= 27 degrees f
    27 degrees f for 404a on a pt chart= 60 +/- 5 psi

    normal estimated suction pressure 55-65 psi
    you are running the proper pressures base on info you put above

    now we can go the next primary symtom hot liquid line, liquid lines if the condensor is working correctly in releasing the heat should have a temperature of 10 degrees over ambient. your units liquid line had a tempertaure of 100 degrees +. this indicates there is no transfer of latent heat of condensor, Now we need to looka the secondary symptoms what is in the liquidline sight glass, is the glass clear of bubbles?

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    Re: 404a high pressure?

    got cut off,

    any way based on the symtoms i would guess that you have non condesables (air or nitrogen) trapped in the system, or you have a overcharge.

    As gary said there are specif weights that manufacturesrs use but does not necessarly mean that holds true to your unit. You will best off performing a controlled charge of the sytem.

    If you have a recovery machine with recycler you may determine if there is non condensables with the the recovermachine gauges based on estimates i gave you on top.

    I hope this info is helpfull. I would be curious as to what you find as well.

    Regards R-T

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    Re: 404a high pressure?

    hi i think i would increase the size off the orrifice in your exp valve

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    Re: 404a high pressure?

    Quote Originally Posted by flyboy3b View Post
    taz,,, i appreciate the help, but the last system i worked on had a site glass and when i found (what i thought) were the optimal settings for that machine, there were bubbles in the glass.
    thanks,
    mike

    With some refrigerants that is somtimes the case.
    As with all things the sight glass is just a tool to be used with all the other tools available.
    With experience the engineer should be able to tell the differance between flash gas and normal opperating conditions.

    taz.

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    Re: 404a high pressure?

    It just occured to me, that you are using R-404a refrigerant in a medium temp application, R404a works more optimal in deep frozen applications.

    If you are wanting to maintain temps of say 32 degrees and above you should, consider r-134a or R- 407c as the refrigerant to be used. It would be the optimum refirgerant for medium temp applications.

    Where R-404a is more optimal for use at tempareatures lower than 32 degreesF.

    If this was done you will have to change the TEV/TXV and pressure switches to accomodate new operating pressures, along with the necessary compressoir oils that are empolyed with there specific refrigerants.

    Just my opinion.

    Regards R-T

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    Re: 404a high pressure?

    Quote Originally Posted by REEFER-TEK View Post
    any way based on the symtoms i would guess that you have non condesables (air or nitrogen) trapped in the system, or you have a overcharge.
    Based on the original numbers, I might be inclined to agree with you, except for the fact that the subcooling was not excessive. This tells us that the there are no noncondensables, nor is the system overcharged.

    The 'condensing temperature over ambient' rule assumes that ambient air is entering the condenser. Upon measuring the temperature of the air entering the condenser, we find that this is not the case. The entering air temp is 91F, not 70F. 91F + 30F = 121F, which is very close to 325psi.

    Either the condenser is in a warm area, heated air is being blown towards the condenser from another unit, or the condenser discharge air is recirculating.

    Flyboy3b is apparently aware that he needs to do something about the warm air entering the condenser.

    Given the very heavy load on the condensing unit, the one thing I am absolutely certain is NOT the problem is... TXV orifice size.
    Last edited by Gary; 02-12-2007 at 07:08 PM.

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    Re: 404a high pressure?

    Quote Originally Posted by Gary View Post
    Based on the original numbers, I might be inclined to agree with you, except for the fact that the subcooling was not excessive. This tells us that the there are no noncondensables, nor is the system overcharged.

    The 'condensing temperature over ambient' rule assumes that ambient air is entering the condenser. Upon measuring the temperature of the air entering the condenser, we find that this is not the case. The entering air temp is 91F, not 70F. 91F + 30F = 121F, which is very close to 325psi.

    Either the condenser is in a warm area, heated air is being blown towards the condenser from another unit, or the condenser discharge air is recirculating.

    Flyboy3b is apparently aware that he needs to do something about the warm air entering the condenser.

    Given the very heavy load on the condensing unit, the one thing I am absolutely certain is NOT the problem is... TXV orifice size.

    Gary, I was basing my opinion on the first topic posted, I would agree that if he has 90 degree air entering the condensor the numbers do look more right.

    I should have probably read more thorouhly, The condensor must be located in a horrible spot if he has 70 degree ambient with 90+ degrees entering it.

    again my apologies.

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    Re: 404a high pressure?

    There's no need to apologize. We all miss things sometimes, myself included. The devil is in the details.

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    Re: 404a high pressure?

    again,, i say thanks to you folks for all your input. let me clarify a few things first,,,
    i built this cooler from scratch,, so i dont really have an idea of what it needs,, im just trying to find the proper balance for this. i dont know if you guys really wanna know the whole story behind this,, but ill give you the short version... and remember,, this is a new field for me.
    ive reconfigured this thing so many times i lost count. i built it in my brothers pole barn which until recently was toasty warm. ive had 3 different cap tubes installed to a point where i thought i had it right (at that point it was a 134a cooler). feeling pretty good about having TUNED my new cooler to perfection, i finished the woodwork and installed the glass and packed it up for installation. by the end of the day, i had it in place,, and it looked grand.
    unfortunately it was not cooling very well, lol. so out of desperation,, i took a NOS (new old stock) 404a condensing unit i had and swapped out the 134a system. i picked up a TXV (i wanted to be able to freeze this flippin wine if for no other reason,,,than just for spite) and filled it with refrigerant. and that brings us up to date,, more or less.
    reefer, there is no sight glass, but i appreciate the input. in case you guys didnt know it,, i write this stuff down that you tell me. its funny,, its all stuff i learned in my classes, but it was harder to remember back then. there is alot to be said for "practical application".
    so heres where were at,,,
    i brought the charge down to about 260 this morning, and got the txv in about the middle ( i gave up trying to get superheat readings until the system stabilizes) and it actually seems like its doing ok. at least its keeping the wine cold. tomorrow morning i will recheck all pressures and temps and post them here. sometimes i get too impatient and i want things to work NOW. what a different perspective there is a day or two later. unfortunately we dont always have time for that (since this is my own work,, i do not have that pressure)
    anyhow,, thanks again. on an even brighter side i got my new fieldpiece datalogger today.

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    Re: 404a high pressure?

    Quote Originally Posted by flyboy3b View Post
    i brought the charge down to about 260 this morning...
    This gives me the impression that you are trying to charge the system by pressure. It doesn't work that way.

    Charging by pressures will not get you into the ballpark or even into the neighborhood of the ballpark. Not even the right zipcode.

    Saturation pressures are primarily a result of the temperature and volume of the air moving through the coils, having very little to do with the amount of refrigerant in the system.

    You need to charge by liquid line subcooling. The proper charge will give you 10-15F subcooling if everything else is right.
    Last edited by Gary; 05-12-2007 at 06:43 PM.

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    Re: 404a high pressure?

    Quote Originally Posted by flyboy3b View Post
    ive reconfigured this thing so many times i lost count.
    In your other thread, I gave you a list of the temperatures needed to tune a system.

    Low side:

    Evaporator air in temp
    Evaporator air out temp
    Saturated evaporating temp (low side pressure converted to temp from a P/T chart)
    Suction line temp at the evap outlet
    Suction line temp near the compressor inlet

    High side:

    Condenser air in temp
    Condenser air out temp
    Saturated condensing temp (high side pressure converted to temp from a P/T chart)
    Liquid line temp near the receiver outlet
    That's the easy way. The way you are doing this is the hard way.
    Last edited by Gary; 05-12-2007 at 05:49 PM.

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    Re: 404a high pressure?

    Let's see if we can translate this into an if/then statement for all the computer geeks out there:

    If the temperature controls call for cooling and
    If the evaporator fan is running properly and
    If the evaporator airflow is adequate and
    If the condenser fan is running properly and
    If the condenser airflow is adequate and
    If the compressor is running and
    If the subcooling is not excessive and
    If the superheat is not too high and
    If the superheat is not too low
    THEN the system is functioning properly

    That's a lot of ifs, isn't it? But that's what it takes to make a basic refrigeration system function properly. On more complex systems the if list can be much longer.

    Note that the superheat is at the very end of the list.
    Last edited by Gary; 05-12-2007 at 06:31 PM.

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    Re: 404a high pressure?

    believe it or not,, i think i am getting smarter every day (my gf might disagree with that).
    here are the most current readings,,,
    ambient 70f
    box 43f (pretty much where i want it)
    air entering condensor 77

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    Re: 404a high pressure?

    sheesh,,,,

    believe it or not,, i think i am getting smarter every day (my gf might disagree with that).
    here are the most current readings,,,
    ambient 70f
    box 43f (pretty much where i want it)
    air entering condensor 77f
    air leaving cond 93f
    liquid line at receiver 101f
    pressure at receiver 280f
    liquid line 3" from compressor 160f
    suction line after evap 47f
    suction pressure 52

    so,, what i see is about 27f of superheat and 9f of subcooling. if i am doing my math right,,, 77f into the condensor coil plus 30f equals 110f which is 271 psig. am i right in assuming that the superheat is still a little high?

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    Re: 404a high pressure?

    Sorry... didn't mean to get preachy.

    280psi = 113F
    52psi = 17F

    113 - 101 = 12F subcooling
    47 - 17 = 30F superheat

    Open up the TXV one full turn (counterclockwise), wait an hour or so (at least 15 minutes if you're in a hurry), then take new readings.

    Hmmmm... I'm wondering how the suction line at the evap can be 47F when it is in a 43F box? It can be colder than the box, but it shouldn't be warmer than the box.

    BTW, that hot line (160F) leaving the compressor is called a "discharge line".
    Last edited by Gary; 05-12-2007 at 07:49 PM.

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    Re: 404a high pressure?

    not preachy at all,, i miss stuff all the time. but once i "understand" it,, then i have it.

    Sorry... didn't mean to get preachy.

    280psi = 113F
    52psi = 17F

    113 - 101 = 12F subcooling
    47 - 17 = 30F superheat

    Open up the TXV one full turn (counterclockwise), wait an hour or so (at least 15 minutes if you're in a hurry), then take new readings.

    Hmmmm... I'm wondering how the suction line at the evap can be 47F when it is in a 43F room? It can be colder than the room, but it shouldn't be warmer than the room

    if i can give you a mental idea of what this cooler looks like,,,, its a 54" wide by 42" tall wall mounted cooler. the cold part is about 42"x42" with 2 glass doors. there is a 12"wide x42"tall part on the right side (like a blind corner cabinet) where the guts are. the condensing unit is at the bottom and the lines feed up to a box that contains the evaporater coil and fan. there is an insulated 5" duct that provides the return air to the evap coil and the evap fan suck the air through the evap coil back into the box. the txv is mounted in ambient air space and the suction line comes out next to it to returns to the compressor. about 6" from the evaporater is where the txv bulb is mounted and where i am taking that 47f temp.

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    Re: 404a high pressure?

    ps,, i will have to wait till after lunch to do any adjusting,, there is a bunch of stuff i have to move to get access to the txv and high side port

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    Re: 404a high pressure?

    The TXV and especially the sensing bulb should be mounted inside the refrigerated area. If the sensing bulb absolutely must be mounted outside the refrigerated area, it should be heavily insulated.
    Last edited by Gary; 05-12-2007 at 08:05 PM.

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    Re: 404a high pressure?

    Quote Originally Posted by flyboy3b View Post
    ps,, i will have to wait till after lunch to do any adjusting,, there is a bunch of stuff i have to move to get access to the txv and high side port
    I'm retired... I can wait.

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    Re: 404a high pressure?

    i had to go down and work for lunch,, so i tore it apart anyways,,, here is the latest,,,
    its not really feasible for me to mount the txv inside the cooled space,, so i will have to insulate. i figured the worst that would happen is that the txv would overfeed the coil and as long as the pressure was low enough,, the temp would be fine.
    anyhow,, one full turn ccw and 30 mins later,,,
    evap in 55f (im not real confident on this reading)
    evap out 43f
    cond in 65f
    cond out 90f
    suction line after the evap 50f
    suction line into compressor 53f
    liquid line at receiver 101f
    pressures are 55 and 275

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    Re: 404a high pressure?

    What is the box temperature?

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    Re: 404a high pressure?

    the box is up to 45f and i just checked the other readings,,,
    evap in 49f
    evap out 44f
    cond in 61f
    cond out 87f
    suc temp after evap 46f
    scu temp before comp 54f
    rec temp 98f
    rec pressure 280
    suc pressure 50
    shouldnt the low side pressure have gone up? and yes,, im sure i turned it one full turn ccw

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    Re: 404a high pressure?

    Why is the cond in temp dropping?

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    Re: 404a high pressure?

    These temperature readings aren't making sense. What kind of thermometer(s) are you using?

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    Re: 404a high pressure?

    im using a fieldpiece hs35 meter with a K-style temp probe, i can try my other thermometer later, just to double check, but the fieldpiece is practically new.
    as far as the condenser temp,, so,, you can picture the wine cooler we have been discussing,, well, under it is a manitowoc Q-210 (air cooled) ice machine. the ice machine vents out the front,, and the wine cooler pulls its air from the back and also vents out the front. but next to the ice machine in the adjacent wall to the right is the cold air return for the furnace. so,,, im guessing,, sometimes the ice machine is running and the furnace is not,, and that corner warms up, and other times,, the ice machine is off,, and the furnace is on,, helping to ventilate that corner.
    anyhow,, its almost 3pm,, and i need to get a nap in before i work tonight. its hell gettin old,, eh?
    thanks again,
    mike

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    Re: 404a high pressure?

    Is there a fan speed control or a fan cycling on/off control on the condensing unit? The head pressure seems to be holding remarkably steady with the cond air in temp dropping from 77F to 61F.

    Does it actually get to 61F in that corner?

    Get a nap... we'll play with it some more tomorrow.
    Last edited by Gary; 05-12-2007 at 11:24 PM.

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    Re: 404a high pressure?

    The fieldpiece should give you accurate readings. When checking line temperatures, strap the end of the probe tightly to the line using electrical tape.

    While we are checking out the system, you might want to put the furnace fan control into fan-on position so that the fan runs continuously, equalizing and stabilizing the room temperature.
    Last edited by Gary; 06-12-2007 at 12:17 AM.

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    Re: 404a high pressure?

    i dont think there is any sort of speed control on the cond fan,, what i think it is,, is when i put this 404a cond unit in,, it was bigger than the coil and comp i pulled out,, so i had to cut out the drywall on the left,, and the plaster and lathe in the back. so in the back of the unit is the bare brick from the outside of the building. ive been to clearwater and clearwater beach many-a-time,, and let me tell you,, its fricken freezin up here in this 120 yr old building in wisconsin, lol
    and i cant do the fan-only thing, ,cause this building cools down in a matter of hours. what i can do,, is try to keep the conditions as stable as possible and take some more readings. i will check it when i go down to work (i live upstairs) and check it again in the morning.
    at this point,,, i am happy that its working at all.
    maybe you wanna get out of that hotness and come to wisconsin for a nice winter break. ill buy you and that female next to you a nice dinner.
    thanks again,
    mike
    www.wavespub.com

    ps,, that area of florida is one of my favorite parts of the US

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    Re: 404a high pressure?

    Quote Originally Posted by flyboy3b View Post
    i dont think there is any sort of speed control on the cond fan,, what i think it is,, is when i put this 404a cond unit in,, it was bigger than the coil and comp i pulled out,, so i had to cut out the drywall on the left,, and the plaster and lathe in the back. so in the back of the unit is the bare brick from the outside of the building.
    You might try to insulate the brick... even a thin layer of plastic would be better than nothing.

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    Re: 404a high pressure?

    Quote Originally Posted by flyboy3b View Post
    maybe you wanna get out of that hotness and come to wisconsin for a nice winter break. ill buy you and that female next to you a nice dinner.
    thanks again,
    mike
    www.wavespub.com

    ps,, that area of florida is one of my favorite parts of the US
    Hmmmmm... winter in Wisconsin... now how could I possibly pass up an offer like that?

    My sweetie is from northern Ohio... and I escaped from Detroit... Soooo...

    Here's a better idea... come on down. But I have to warn you. The winters are brutal here. This morning, for almost three hours, I had to wear a sweatshirt... brrrrrrr...

    BTW, that picture was taken last year at an outdoor Xmas party (hence the festive SantaSkull T-shirt).
    Last edited by Gary; 06-12-2007 at 06:16 AM.

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    Re: 404a high pressure?

    gary,,,,,,,,,,, remember,,, the brick you want me to insulate right now is about 35f. there is no insulation in this old building. the times that the "in" temp to my cond coil is when the outside temp is overtaking the inside temp.
    next spring we may have this same conversation, lol

    ps,,,i brought my electrotherm digital thermometer down tonight,,, and in most cases,, it was within a degree or two of the readings (side by side) with the fieldpiece.
    i wonder how often technicians take so many readings so close together. this is more of a pet project for me,, i guess. my first project.
    anyhows,, its 1am and time for bed

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    Re: 404a high pressure?

    How do the temps look this morning?

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    Re: 404a high pressure?

    Quote Originally Posted by flyboy3b View Post
    i wonder how often technicians take so many readings so close together. this is more of a pet project for me,, i guess. my first project.
    In truth, the average tech takes very few readings and wouldn't know what those readings mean anyway. They fix the obvious problems and never tune the system. If/when it puts out cold air, they take the money and run.

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    Re: 404a high pressure?

    here is the latest set of measurements,, and i went out of my way to verify them,,,, and for what its worth,, its seems like its doing ok.
    box temp 44f
    evap air in 55f (still seems high to me)
    evap air out 44f (it seems like that should be a little lower as well)
    cond air in 65f
    cond air out 90f
    liq line at receiver 98f
    suc line after coil 48f
    suc line at comp 63f
    pressures at 55 and 280 psig

    looking back at my other measurements,, the suction line temp didnt change much after that txv adjustment, in fact,, none of the temps changed much. the txv is still icing up but not excessively. the system is run by a line voltage thermostat (right now i have the bulb a little too close to the evap coil so it turns on and off about every 25 min mins depending on usage).
    anyhow,, i have to run out by my brothers house and help him install a snowblower to his john deere and ill check back a little later to see if anybody wants to throw their two cents in.
    thanks again,
    mike

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    Re: 404a high pressure?

    I would place the thermostat bulb near the return air duct. That alone should make a big difference.

    Set the thermostat to 35F. Let's see what the system does in a "normal" temperature range.

    I'm assuming the evaporator fan runs non-stop... even during the off cycle? If it doesn't, it should.

    Actually, the numbers look a little better this morning.
    Last edited by Gary; 06-12-2007 at 09:35 PM.

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    Re: 404a high pressure?

    Quote Originally Posted by flyboy3b View Post
    evap air in 55f (still seems high to me)
    Actually, it makes more sense... and this is the temperature that the thermostat bulb should be sensing and controlling.

    Quote Originally Posted by flyboy3b View Post
    evap air out 44f (it seems like that should be a little lower as well)
    Not if the air in is 55F.

    Hmmmm... here is a new temperature measurement for you to take: Locate the copper return bends along the side of the condenser. Read the temperature of the center return bend.

    Also, measure the temperature of the liquid line near the TXV.
    Last edited by Gary; 06-12-2007 at 09:30 PM.

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    Re: 404a high pressure?

    man o man,, talk about cold and wet. it took us 2 hours to hook up this blower. have you ever looked at the underside of a john deere tractor with a snowblower on it? theres a belt thats about 10 feet long that serpentines through all these pulleys, a bunch of cotter pins and some strange looking arms with pins and holes.
    the problem is that neither of us have ever seen it installed and we dont have a manual. anyhow,, all is well,, and the snow is gone.
    back to reality,,, gary,,, i bought the thermostat from american scientific (like an army surplus for electronics) for 5 bucks. its a ranco controller and i think it was designed for high temp applications. so i opened it up and adjusted the contacts to close at around 35f giving me about a 10 degree differential. the problem is that i think when i adjusted beyond the design range of the switch,, it through off the sensitivity of the switch. as i move the switch further away from the evap coil,, it takes exponentially longer for it to shut off, causing ice build up on the coil. but yes,, i agree,, it needs to move further away. once everything else is up to snuff,, i will start playing with that.
    i will try to get back into the cooler this afternoon. it takes a little time because i have to disassemble the shelves on the cabinet to the right, but we can try another full turn ccw and see what happens.
    in the meantime,, im gonna dry out my shoes and try to warm up a bit. there was something else i was gonna say,, but i forgot what it was.
    thanks ,
    mike

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    Re: 404a high pressure?

    i just remembered what it was,,,
    i can take those temps on the loops, but i have to take a cover plate off to do it and it will read high because of the ambient air entering the evap coil. but the readings should be relative to how much refrigerant is in the coil, sort of.

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    Re: 404a high pressure?

    Let's cancel the TXV adjustment for now. And the loop measurement I want is on the condenser coil, not the evaporator coil.

    Thinking about your surplus thermostat with the 10F differential and just shaking my head. You need a real thermostat... and about a 3F differential.

    When you say "near the coil", please tell me you have it sensing coil inlet temperature and not coil outlet temperature.

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    Re: 404a high pressure?

    Quote Originally Posted by flyboy3b View Post
    man o man,, talk about cold and wet. it took us 2 hours to hook up this blower. have you ever looked at the underside of a john deere tractor with a snowblower on it? theres a belt thats about 10 feet long that serpentines through all these pulleys, a bunch of cotter pins and some strange looking arms with pins and holes.
    Being a city boy, I've never seen the underside of a john deere tractor... but I did kick a charging bull one time... and lived to tell about it... lol
    Last edited by Gary; 06-12-2007 at 10:18 PM.

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    Re: 404a high pressure?

    hey,, i paid 5 dollars for that thermostat, lol. actually,, i do have some other thermostats i can use,, its just that they were designed for switching 25 amps,, and id rather save them for other projects i have. the way its set up now,, it cycles on for a bout 5 or 6 mins,, and shuts off for about 15 to 20 mins.

    getting readings off the condensor might be a little harder (its tucked back in there pretty good,, but i will try

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    Re: 404a high pressure?

    yes,, the evap fan runs all the time,, its my only protection against freeze up.

    no,, if i moved the sensing bulb for the thermostat to the return air for the evaporator,, i would have to readjust the contacts back close at a higher temp.

    and no,, the john deere is a not like a big tractor,, more like a big lawn mower.

    and ive seen alot of bull as well,, but probably not the kind that you mean

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