Third comp change in three years, why?

[expat]

I got called to a customer last Friday as his cold room was no longer cooling.

He said that the fire brigade had broken-in in the early morning and tripped the whole place out due to an alert from a neighbour of smoke coming from within. Nothing to do with the cooler though.

On arrival and after resetting the main trip switch they found that the cold room comp wasn't running.

When I got there I found the contact relay (KM1) was energized but 0V across the three phases. I found the trip switch before this was out so I tried to reset it but it wouldn't have it. After disconnecting the comp the trip switch stayed in, and I was getting 400V across the disconnected wires. So, after checking windings' resistances concluded: comp change.

Got the comp in the morning and changed it out in the afternoon. Now he waits until I've finished (chopping, modifying, brazing, pressure testing, fixing leak, re-pressure testing, vacuuming, charging) to tell me that this is the third time in three years!

So, after I got it up and running a gain I start gathering info to try and work-out the cause.

Calculation for room 2759W
Condensing unit unité TAJ4519ZHR 404A 2771W@ -5°C
Evap Friga Bohn MUC420 4600W

Seeing this mismatch I go back and find the TXV is a TEX2 R22.

Before filling in the details on the comp autopsy, running temps and so on I wonder if anyone has anything to say about this set up and the life span of the compressors?

[The Viking]

Might be silly but it's often overlooked...

Did you do an acid test on the oil from the old pot?

[Grizzly]

Might be silly but it's often overlooked...

Did you do an acid test on the oil from the old pot?

Seriously good point there viking!
A lot of people seem to think a oil and filter change is suffice!
It does sound like a serious case of cross contamination.

Just another thought also, are these replacement comp's remans?
If so whose?
Grizzly

[expat]

Thanks for the quick replies.

I used one of those QwikCheck things from ITE.

It didn't change colour but I wonder how reliable they are. First I used it on the system after repair. Then dipped it in the oil.

[expat]

I'm not sure I know what you mean by "remans".

[ultralo1]

How much refrigerant is SUPPOSED to be in it? What does the data plate say?

[expat]

I pulled 1.96Kg out. Name plate was illegible. The liquid receiver is 2.35dcm3

[chemi-cool]

When too big evaporator is used, to get a clear sight glass, you charge almost 1.5 times the refrigerant required.
TEX 2 R-22 is not such a big mismatch, only by a few %

If you cut the pot open, I believe you will find on the discharge flappers, evidence of liquid hammering.
The evaporator is twice the size.

And please do as the Viking says, this test should be a routine every time a system is opened.

[Gary]

The oversized evap might be overloading the compressor during pulldown. Easiest solution would be a CPR valve.

[expat]

Thanks Chemi, I take it you don't trust the Qwikcheck set so I will go and test the oil now. I filled a clean jar up with a sample. Be right back!

[ultralo1]

I dont know if this will help but, I had a 20ton chiller eating compressors. 3 in three years. Everytime I changed the comp I would valve off the suction and discharge lines and evacuate them. Change the comp, open the lines and recharge by the site glass and pressures.

On the fourth comp I had the time to recover the entire charge. I recovered 45 pounds, the name plate called for 100 pounds. I called the manufatcurer and they said 120pounds. There were no leaks. The system had been running with half a charge and it had been cooling the unit it was connected to. The factory believes this is why it was eating comps. I charged the system with 100 pounds and it is know working correctly. Alot of the problems that I had with it have disappeared.

Never mind, just saw the mismatch for cond to evap.

[expat]

Chemi, Viking, Grizzly, the acid test shows up marginal.

Oil is discoloured darkish brown. There is a smell of overheating but not burning.

No short - meggered 20GOhms. Resistances 1-2 560ohms, 1-3 140Ohms, 2 - 3 690Ohms. Readings should be 8.7Ohms @ 20°C.

Plastic insulation between windings overheated and brittle. Internal thermistor protection was not hooked up in series with the contact relay.

Chemi I can't see any signs of mechanical damage other than one of the suspension springs was broken.

[expat]

Thanks for the input Gary.

Ultra, if I put more than was in there in the first place I won't I have too much for the 2.35dcm3 liquid receiver?

[Gary]

Did you replace the contactor?

[expat]

Gary, could you explain this a little. As at the moment It's evaporating at -19°C/28.4°F. for a positive cold room. 17K superheat at evap and 24K at comp suction.

[expat]

No I didn't Gary. I must admit it did give off a bit of a spark. Sorry it wasn't the contactor it was the trip switch that gave the spark when I tried to push it back in. The contactor cidn't have a problem.

[Gary]

When a compressor burns out, heavy amperage passes through the contacts. Burnt contacts can provide low voltage to the new compressor, causing another burnout.

At the very least, you should check the running voltage at the compressor terminals.

[expat]

Thanks for that Gary I can't remember if I checked it once it was running again but I will.

[expat]

Gary, what is your idea with a cpr? Can't find out what this means in English and I learn't refrigeration in France.

[Gary]

A CPR is a crankcase pressure regulator. It is installed in the suction line to limit the pressure entering the compressor and therefore the load (and amperage draw) on the compressor.

[Gary]

An alternative solution would be a TXV with maximum operating pressure (MOP) charge. The TXV you have is probably too large for the condensing unit anyway.

[expat]

Ok, thanks Gary. I'm going to sleep on this and mull over your suggestions.

I thought when I started this thread that there would be a unanimous cry of "too much system superheat" under high ambient/load conditions due to an oversized evaporator.

I mean to say, 1 comp per year! I thought the reason was going to be easy to see. Anyway I can start by double checking the voltages.

Thanks again to all.

[Gary]

Check the amperage, too.

And while you're at it, check the following:

Low side:

Evap air in temp
Evap air out temp
Saturated suction temp (SST) converted from pressure
Suction line temp at evap outlet

High side:

Cond air in temp
Cond air out temp
Saturated condensing temp (SCT) converted from pressure
Liquid line temp at receiver outlet

[nike123]

If it is TEX 2 with orifice 01 than valve capacity is OK for pressure drop at lines of 0,5bar and condensation around 40°C.




If you have this valve body codes than you have also valve with right MOP.

[Gary]

According to the Danfoss chart, this TXV has a MOP of -4C to -5C, so the compressor should not be overloaded during pulldown.

With a coil outlet superheat of 17K and SST of -19C, that would put the suction line temp at -2C, which is presumably below the cold room temp. This tells me that the coil is not so large as to prevent the TXV from modulating.

So far so good. Let's see what all the numbers look like when the cold room is down to temperature.

[expat]

evap air on 1.6°C/35°F
evap air off -1.4°C/29°F
sst -19°C/-2°F
Suction line temp at evap outlet 2.3°C/36°F

Ambient 23.5°C/74°F
Cond air in temp 26°C/78.8°F
Cond air out temp 36°C/96.8°F
Saturated condensing temp (SCT) converted from pressure 42°C/107°F
Liquid line temp at receiver outlet 35.7°C/94°F

Amperage only taken during pull down 3.2A against 3.9Anominal

Thanks NIke. Did you see the system is running on 404A though?

[expat]

Sorry lads I just noticed a problem with the air on temp and the suction leaving evap temp. I most have made a mistake in my notes somewhere. I'll have to check this.

Thanks for your help.

[Gary]

Hmmm... this is starting to look like a restriction. If there is no temp drop across the drier, I would check the TXV inlet screen. But then, I assume you changed the drier... so that leaves the inlet screen.

[nike123]

Thanks NIke. Did you see the system is running on 404A though?

Nope, I only concentrated at TXV valve for now!
Does that mean that you have R404A in system?
If that is the case you should change valve to R404A type.
That must be TES 2 with 02 orifice and MOP
Valve body# 068Z3407
Orifice # 068-2015

[expat]

Right, it seems I had already written -1.3°C and crossed it out and wrote 2.3°C in it's place. I can only imagine that the comp had shut down and that 2.3 is the mistake.

[expat]

No Gary, I haven't checked the screen. Perhaps I should then!

Nike, yes the system is running on 404A. I've got a TES2 orifice No 2 but not with MOP. System still running with the TEX2!

[nike123]

This is what you should have at design conditions.

[Gary]

Seems we have narrowed it down to TXV problems. Replace with the proper R404A TXV with MOP.

... and check the inlet screen on the old TXV just to satisfy my curiosity.

[nike123]

Nike, yes the system is running on 404A. I've got a TES2 orifice No 2 but not with MOP. System still running with the TEX2!

Then change valve! That is high temperature unit and should easily cope with higher evaporation temperatures (and capacity) therefore I think there is no explicit need for MOP valve.
Also, I don't think that evaporator and condenser unit is grossly mismatched because at higher evaporation temperatures (0°C) and lower evaporator TD (6.5K) they are pretty much matched.

Edit:It is mismatched highly. I got something wrong at first. It should be MUC280.L

Question is what is original purpose of this setup?
Only obvious wrong thing here is TEV (for now).
Why is there TEV for R22! Does someone worked before on that unit?

If orifice in present TEV is 02 than this system is combined from two plants. One system has got previously evaporator with R22 valve for 4,5-6 kW with lower TD (7-8K) and other is condenser unit from other system with R404A for high evaporation temperatures (7°C) and simmilar capacity for that conditions. (4,9 kW) But here for -5°evaporation these two is mismatched by 1/2 ratio. Also for -5°C this evaporator doesn't have appropriate fin spacing for that intended purpose! It has 4,23 mm instead of 6,35 fin spacing.

It is probably that this is commissioned from available second hand parts and matched for high temperature application with low TD (mushrooms plant conditioning for example) and technician leaved old TEV with only adjusting superheat. Now it got his who-know-what-in-order new role in its turbulence life.

[Gary]

I agree that the TXV should be replaced.

That said, given the TXV/refrigerant mis-match I would expect the SST to be running around -10C rather than -5C. Given the heavy load, -19C says restriction.

[chillyblue]

Sounds like the valve could be incorrectly set/ running with too high a superheat. I would definately change the valve to a R404A valve.

CB

[US Iceman]

evap air on 1.6°C/35°F
evap air off -1.4°C/29°F
sst -19°C/-2°F
Suction line temp at evap outlet 2.3°C/36°F

Are these numbers correct?

[Gary]

Apparently, the 2.3C was in fact -1.3C. Actually, the 2.3C seems more likely.

[US Iceman]

Let's see here...

Calculation for room 2759W
Condensing unit unité TAJ4519ZHR 404A 2771W@ -5°C
Evap Friga Bohn MUC420 4600W

and

evap air on 1.6°C/35°F
evap air off -1.4°C/29°F
sst -19°C/-2°F
Suction line temp at evap outlet -1.3°C/29.6°F

First question is: was the SST measured by temperature or converted from pressure?

Second observation is: The compressor capacity is about 60% of the evaporator capacity. The re-balance in evaporating pressure should be much higher. This would force the saturated evaporating temperature much higher also. When this occurs, the suction pressure should increase. This would raise the compressor capacity and heat rejection on the condenser also.

My first guess based on this information is this: Someone threw this system together haphazardly. When the system did not work, they throttled down the TXV thinking the suction pressure would drop. Along this line of thinking they forced the evaporating temperature down to what they expected to see.

By doing this they artificially increased the superheat, so now the compressor runs hot and just breaks due to heat fatigue.

There might be sufficient mass flow to provide some minor cooling effect for the cold room, but because of all of this the compressor life is greatly shortened.

[Gary]

It seems we all agree that not enough refrigerant is flowing through the TXV. Whether this is caused by improper adjustment or restricted inlet screen is interesting but academic because, as Nike pointed out earlier, the TXV needs to be replaced and that will solve the flow problem.

Once the TXV is replaced we can get a new set of measurements and see if there are further problems.

[nike123]

I edited this post!

Then change valve! That is high temperature unit and should easily cope with higher evaporation temperatures (and capacity) therefore I think there is no explicit need for MOP valve.
Also, I don't think that evaporator and condenser unit is grossly mismatched because at higher evaporation temperatures (0°C) and lower evaporator TD (6.5K) they are pretty much matched.

Edit:It is mismatched highly. I got something wrong at first. It should be MUC280.L

Question is what is original purpose of this setup?
Only obvious wrong thing here is TEV (for now).
Why is there TEV for R22! Does someone worked before on that unit?

If orifice in present TEV is 02 than this system is combined from two plants. One system has got previously evaporator with R22 valve for 4,5-6 kW with lower TD (7-8K) and other is condenser unit from other system with R404A for high evaporation temperatures (7°C) and simmilar capacity for that conditions. (4,9 kW) But here for -5°evaporation these two is mismatched by 1/2 ratio. Also for -5°C this evaporator doesn't have appropriate fin spacing for that intended purpose! It has 4,23 mm instead of 6,35 fin spacing.

It is probably that this is commissioned from available second hand parts and matched for hight temperature application with low TD (mushrooms plant conditioning for example) and technician leaved old TEV with only adjusting superheat. Now it got his who-know-what-in-order new role in its turbulence life.

[expat]

Hi Iceman, the -19°C SST was converted from pressure taken at comp suction. Between this and the evap is about 10m of 1/2" pipe with white air conditioning type insulation.

Both liquid and suction lines have been bent and twisted by hand in a shoddy manner. Given the uninspiring visual aspects of the system I wasn't surprised to find hidden faults.

The owner of this equipment has a profound mistrust for any professionals. And he is, I'm sure, partly to blame for his misfortunes.

For example, Nike, you said
"Then change valve!"
I would love to but I told him that as the evaporator was over sized this would only be a first step and that I couldn't guarantee that doing this would solve the comps burning-out. So he said to come back in April

Sorry to whine on like that it's just there is a difference between what we discuss here and what the client will agree to. I know it sounds ridiculous, especially in this case as the client knows that his system set up will be the cause of another premature comp failure.

As far as my temperature measurements are concerned I took my time and am confident with them. All except the leaving evap temp. The -1.3°C was being read by a wireless transmitter hooked up to a type K. When I was ready to leave I connected the type K directly to my thermometer and got 2.3°C. So, I was suspicious of the transmitted reading and chose to record the direct one.

Now, I'm going to reiterate my understanding of this system.
I think that at the current ambient temp of 23°C and without a heavy load to pull down the comp is running outside parameters but is getting 4.5°C temp at suction inlet. So, I don't think it is not suffering.

Next I think that in high ambient and pull down conditions it is probably evaporating at a higher pressure and getting a higher suction temperature at the comp inlet. This being insufficient to keep the comp cool it starts to over heat.

Now as I said the internal thermistor protection was not wired up in series to the coil on KM1 contact relay so was not able to cut the comp out when it was overheating.

Add to this the thought that the client is exaggerating about the number of change outs he has had to make (maybe it's more like every 18 months) then it starts to look like the comps wore out due to poor system design, and lack of protection.

When I go and get my check I will try and urge him again to change the valve. But I think this will still leave me with a good portion of the evap effectively becoming part of the suction line and consequently giving high superheat at comp inlet.

If this were to happen the choices I gave the owner were to change the evap or try to reduce it's capacity.

I thought the last option would be possible as the evap is designed like this:
From the TXV there are several large capillaries distributing the refrigerant to separate horizontal sections, one layered on top of the other.
The first cap feeds the bottom section weaving left to right until it gets to the back of the evap where it feeds into a vertical header.
Next section above this does the same and so on and so forth until the top.
So I thought it looked viable to snip off the caps feeding the top one or two sections thereby reducing the surface of the evap as they would no-longer be receiving refrigerant.

I hope this idea doesn't make people roll their eyes' and say I'm worse than the guy who went there before me!

[Gary]

At the very least, I would check the TXV inlet screen. The refrigerant flow needs to be increased.

You may not be able to adjust the TXV superheat due to the coil oversize. If the coil has multiple fans, you might try disabling one in order to reduce the coil capacity and adjust the superheat. Be sure to wait until the refrigerated space is near design temp before adjusting the superheat.

A more permanent means of adjusting coil capacity would be to find fan blades with a shallower pitch. Less airflow means lower capacity.

Disabling the top runs of the coil would be an acceptable alternative.

[expat]

Nike, I've hypothesized as to the whys and wherefores but frankly it's a waste of time when you see some of the things in this place.

For example he had a toilet that he thought was leaking because when he flushed it water appeared around his feet. In fact the thing simply wasn't hooked up to the sewers. It just flushed out behind the drywall (or not so dry wall)!

Another example. The first job I did for him was to change out an old a/c unit. Indoor was the ceiling type.

It looked good so flush with the ceiling. But when I started to dismantle it I found the ceiling was 4cm thick of plaster or glue or something hard. The indoor unit was plastered into the ceiling and when I finally got it out literally piece by piece I found the control buttons buried in the plaster.

[expat]

Thanks for that Gary.

I realise, what ever happens, I should at least go back and check the screen. I'll fit it in next week and update.