new compressor high pressure relief valve opens at 220 psi

[arnout]

Dear friends,

On a R22, 3 Ton, ductable air conditionning unit, runnig fine since 7 years, the internal high pressure relief valve of the copeland scroll compressor ZR28K3 started opening while the high pressure was only 220 psi and low pressure 20 psi.
Thinking that the compressor's valve was faulty, we changed the compressor.
After installing the brand new compressor, the problem remains...
Thaught the condenser could be blocked (as the HP gage is downstream to the condenser), so i brased a 1/4 valve on the discharge line and connected one more HP gage between the compressor and condenser.
While running the compressor with HP valve closed, both my HP gages (before and after the condenser) were rising at the exact same speed and the IPR valve openned again when both the gages showed simultaneously 220 psi. Which means that the condenser is not blocked.
i have also flushed the condenser twice.
The IPR valve is supposed to open at a pressure differential of 375 to 400 psi according to Copeland.The (3 phase) compressor amps are of 4.2 while IPR is closed and 4.0 when it opens. The maximum running current is of 5.8 A for this compressor.

Has anyone encountered this problem?

Thanks for your help.

[AlexG]

It seems your evap T is -20C and cond T is about 43C. If you check Copeland Users manual this value is a limit for R22.
Cheers

[passandscore]

Are you sure it's the internal relief and not the internal thermal disc that is bypassing the gas? The ZR28K compressor has an internal thermo-disc (discharge gas temperature protection). This thermo-disc opens a gas passage from the discharge port to the suction side near the motor protector when the discharged gas reaches a critical temperature. The hot gas then causes the motor protector to trip shutting down the compressor.

Low suction pressure will cause your discharge temperature to rise which leads to the internal thermal protector opening, equalized pressures and the misconception that the compressor is faulty.

If this is the case I would start by increasing the suction pressure. Perhaps you are low on gas!

See attached:
Scroll Compressors for Air Conditioning (http://www.emersonclimate.com/europe/ProductDocuments/CopelandLiterature/C060219_0909_0411_E_AGL_AC_Scroll_FULL_9.pdf) (pg15)

[arnout]

It seems your evap T is -20C and cond T is about 43C. If you check Copeland Users manual this value is a limit for R22.


Hey, thank you for your attention.
What do you mean by a "limit value"?
Does it mean that the IPR is supposed to open? or does it mean that the compressor shouldn't run in this context for a long time? (which would surely make it over-heat)
In the ZR28 user manual, i saw that the HP and LP differential pressure should be between 375 and 400 psi in order to open the IPR. But in my case we have just 200 psi...

[arnout]

Are you sure it's the internal relief and not the internal thermal disc that is bypassing the gas? The ZR28K compressor has an internal thermo-disc (discharge gas temperature protection). This thermo-disc opens a gas passage from the discharge port to the suction side near the motor protector when the discharged gas reaches a critical temperature. The hot gas then causes the motor protector to trip shutting down the compressor.

Low suction pressure will cause your discharge temperature to rise which leads to the internal thermal protector opening, equalized pressures and the misconception that the compressor is faulty.

If this is the case I would start by increasing the suction pressure. Perhaps you are low on gas!


Thank you for your attention and for the link.
Didn't know about the gas bypassing thermal disc, but one more thing: the compressor runs, it doesn't shut down, simply the HP stabilises at 200 psi.

Increasing the gas was the first thing i did, but however much gas i've put, the LP wouldn't exceed 20 psi.
First thaught of some obstruction in the line but after:
-changing the strainer
-cleaning the TEX orifice and filter
-openning the TEX fully
-flushing the entire system
The LP still wouldn't exceed 20psi...
Could it be that the LP doesn't exceed 20 psi because the HP is not high enough?
Yesterday we changed the condenser (we had one as spare), but it didn't change anything.

One more question:
To check a compressor's compression, one can run it for a very short time with the suction line open to free air and HP gage braised on the discharge line, right?
In the case of this compressor, like on a healthy compressor, the HP rises very fast and the IPR won't open until the HP reached 350 psi (didn't risk it more than 300 psi thou)
This test can also be performed with the discharge line connected to the condenser and HP gage at the other end of condenser, right? When i do that the pressure usually rises slower but still easily exceeds 300 psi.
In the current case, the pressure doesn't exceed 200 and a "pshiiit" sound is heard from inside the compressor.
Do you think that the gas bypassing thermal disc can get overheated so fast? (less than 30 secs.)

[nike123]

Is that heat pump air conditioner? If yes, sound could come from 4-way valve,but in that case suction pressure will be high.
Are you sure in low pressure reading of 20 PSI? It looks like there is no heat load at evaporator and therefore low evaporating temperature/pressure.

First thing to do is to clean evaporator thoroughly and than to check for correct air flow at evaporator as per manufacturer specifications. Same goes for condenser side. Than put your unit in test mode, or at highest air flow (if it is non-inverter type).
Only after that you can proceed with measuring and troubleshooting.

Than, if it is possible, without tripping compressor safety, we need full set of measurements:

Air temperature and humidity entering evaporator
Air temperature and humidity leaving evaporator
Low side pressure and where is taken.
Liquid line temperature at entrance to evaporator
Gas line temperature at exit of evaporator
Gas line temperature at entrance to compressor
Compressor discharge line temperature
Condenser entering air temperature
Condenser leaving air temperature
High side pressure and where is it taken
Liquid line temperature leaving condenser
Liquid line temperature entering TXV
Compressor current
Compressor voltage balance

[AlexG]

Arnout, are you sure you charged it with R22 not R134a? :)
Or probably you need to replace TXV complete, not only orifice... Explain how IPR opening looks like. And nike is right, the more data you give the easier to find solution...

[passandscore]

The original compressor was a ZR28K and you replaced it with what? I'm not sure that the ZR28K is still available. Does the new compressor have the following sticker?


11087

If so, I recommend you read the following literature:
http://www.emersonclimate.com/asia/en-AP/Products/Compressors/Scroll_Compressors/Commercial/Documents/astp_overview.pdf

If the above information is still relevant, watch the video for a visual understanding.


http://youtu.be/_D1OlE1yWoY


As for the test you performed, it is conceivable that the thermal disc did open. You had atmospheric pressure upon the inlet, high compression ratio, and no motor cooling. Not to mention no oil return, so excessive friction was present. If you are absolutely certain that you have the right refrigerant charge, I recommend that you run the system and take the measurements as requested by nike123. Only then can we assist you further.

[RANGER1]

arnout,
Probably not a good idea to pump air through compressor as it could damage or overheat oil & components quickly.

Use nitrogen in future of test with system.

Agree with everyone's need for more information, maybe watch amps too.

From watching video & if thermal disc opens, compressor stops pumping, suction pressure should increase!

Assume you are measuring suction pressure at compressor inlet

If system is left off does suction pressure increase to significantly higher pressure, what is it after say 30 minutes?
When system starts does suction pressure steadily reduce to 20 psi, or quite quickly?

Can you measure pressure inside evaporator, very important?

From reading all previous posts it nearly sounds like you have a restriction in suction line like a crankcase pressure regulator!
Can you see any type of valve in suction line?

Another compressor test would be to close or retsrict suction line too compressor & see if compressor suction drops below 20 psi.

[arnout]

Dear All,

Thank you very much for your help.

-The system cools only, it doesn't have a 4 way valve.
-This compressor doesn't have the ASTP sticker, but i think it has the technology inside since i've been facing this problem.
-The ZR28K is available here as i am in India and that all R22 products are still available and are even produced!
This could explain why the manufacturers would have omited to put the ASTP sticker...

Following your advices, i made the running HP test again with 50 psi of nitrogen on the LP side and the inner valve didn't open, the HP easily rose up to 250 psi (then i stoped it).
This really confirmed that the problem was due to very low pressure on LP side.
i've then put back the first condenser, changed the TEV and orifice, and ran the system with cooling coil fan at full speed.
The system is working perfectly and even after setting the fan speed frequency at 28 (for noise reasons) the LP is stable: around 65 psi.
It was the TEX that was faulty and still can't believe i didn't find the problem.

Thanks again to all of you.

Long life to RE!

[passandscore]

Good to hear! Thanks for the letting us know the outcome.