low suction

[proby]

I have a trane condensing unit with 2 scroll compressors. These compressors share one suction line. with one compressor running the suction is 70 psi and its r-22 running ac. But when the 2nd compressor comes on the suction drops to 50 psi. the second compressor feeds 2 txvs so does the 1st these are 2 seprate liquid lines but one common suction line. do i need to adjust my txv for the low suction or is this ok.

[Grizzly]

Hi Proby
Given that 70psi = 42f / 5c
and 50psi = 26f / -3c.
I would say that system 2 txv's may need adjusting slightly.
Have you checked their s/heat setting?
Grizzly

[taz24]

I have a trane condensing unit with 2 scroll compressors. These compressors share one suction line. with one compressor running the suction is 70 psi and its r-22 running ac. But when the 2nd compressor comes on the suction drops to 50 psi. the second compressor feeds 2 txvs so does the 1st these are 2 seprate liquid lines but one common suction line. do i need to adjust my txv for the low suction or is this ok.


Before you jump in and adjust things you need to go back a few steps....

When did the suction pressure start to drop?
Has the system worked ok until just recently?
Is there a filter in the comon suction line, a strainer or a check valve?

You need to ask why it is doing what it is doing!!!!

Why do you assume the TEV (TXV) needs adjusting.
TEV's do not normaly need altering if they were ok.

Questions to your questions :p but don't jump in and adjust.

Find the reason and then act acordingly.

All the best

taz

.

[Brian_UK]

Also, what are the pressures/temperatures when the 2nd compressor is run on its' own?

[lana]

Hi,

If second compressor comes in and suction drops, it's because of low cooling load on the evaporator. This is why two compressors are used instead of a big one; for capacity control.
If evaporator capacity is less than the compressor capacity then suction drops and so capacity control is required.
Check the thermostat setting which runs the second compressor.
If you are sure it's not because of this reason then look for some other faults.
Cheers

[FEISTY]

Since I usually keep my opinions to refrigeration questions, this is how I handle the same problem with my equipment. Try isolating the compressors and have comp. #2 act as primary. That way you can inspect the operation when it is on its own, just as comp. #1 runs alone. Now you are able to compare specs and see how it operates. Thanks Taz. My past posts about TXV problems are usually answered the same way. Don't jump to turn a screw, knob, handle,valve,etc. just to see IF SOMETHING DIFFERENT HAPPENS. You " open up a can of worms " you usually can't get out of. Do it because you can explain it. Not apologize for it. Good luck.