erractic pressures

[jdere]

Hi guys,
I have a 10 ton r-22 air condtioning console unit with 2 compressors (2 evaps,one condensor) working in tandem, the first compressor has normal low and high side pressures for the indoor and ambient temperature.As the load rises during the summer months the second compressor kicks on and by the end of the day the 2nd evap is iced over.I noticed the low side pressure is going up and down(slowly),with amp meter showing a corresponding rise and fall in the amp draw of this 2nd compressor (until the end of the day when low side is very low and steady).At the start of the day both pressure are normal ,if I try to add even a little bit of r-22 ,the high side will cut out. The first compressor is running normally,both evaps are very clean,including the condensor. I noticed someone has replaced the TXV valve on piping of 2nd evap ,other than that the whole system is original, chysler american, at least 40 years old. Replacing the system is not what the owner currently wants to do.Can anyone point direction to go with this? Thanks

[airworx]

cannot troubleshoot refrigeration problem without subcooling and superheat, and that has to done with machine fully loaded. need both.

[service guy]

Temp splits across Evap also would be a good thing to post as well.

[hvacstress]

Try to change the work order meaning to swap the compressors and see what gone happened.
Isolate them one by one and check superheat ,amps, check for restrictions ,compare the results and try to restrict or improve airflow across evaporators.Compare the load and then ....
Let us know what you find out.
Do you have any check valves or solenoids and how they work in the system?
Maybe one of the txv’s are not within range or have strainer blocked out. .

[hvacstress]

Load amps up and down and pressures are symptoms of none condensables.

[rob provost]

Make sure your sensing bulb is in the right place and is well insulated, pressures jumping around is normal for the first 15 minutes with a TXV. If after 15 minutes and its still bouncing you may have a problem with the power head on the valve. Also the TXV that you said was changed may be too small. Check numbers on other valve.

[jdere]

I checked the model #'s of Txv 's and they match. Its going to be diffcult to check proper temp and pressure ,because its winter here in Boston. I was just trying to do some troubleshooting before season begins.

[Carrene #2]

Whose to say the relaced TXV was setup properly? That's where I'd start. If there is some history with this unit, try and sort out sequece of events.

[jdere]

Your right r718, Maybe it was not vacuumed correctly or maybe something caught in strainer. I will recover gas and check out TXV and put under proper recharge.
Because of the age of the compressors ,I was worried that the hermatic compressor had lost some capacity,but it read proper amp load (last season).