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CommercialHvac
21-05-2013, 11:52 PM
I'm having a problem with one of three compressors on this unit; Circuit one and three compressor screw cover plates are cold and sweating, circuit 2 compressor is hot to the touch. All three liquid injection solenoid valves are NOT energized, which I thought they stayed on while the compressor was running. In operation manual sequence of operation states that liquid line S.V. and liquid injection both energize on start up. Can anybody help me with this problem? I thought for sure the problem with circuit 2 compressor was due to no liquid injection until I discovered circuits 1 and 3 liquid injection was not energized also.

The Viking
21-05-2013, 11:58 PM
Circuit 2 is short of charge??

:cool:

Grizzly
22-05-2013, 06:02 AM
Keeping late hours again Norseman!
As the Viking states CH your system is likely to be short of gas.
The other thing is, is the liquid injection for say oil cooling or is it a economiser port?
Which boosts the operating range of the compressor and on most of the comps I see.
Has it's own range at which it operates.
Typically their solenoid valve opens at say 60 - 80% load.
Some have to see a minimum "Economiser / Flash tank" level.

I would check out as the viking suggests first though!

Have you also considered that 2 comps can be at 75% load with the 3rd off?

10371

Grizzly

CommercialHvac
22-05-2013, 11:19 PM
Grizzly,

Thanks for your response.

The liquid injection is for compressor cooling, which gets hot due to the oil. All three compressors were running at the time; circuits 1 and 3 were at 50% and circuit 2 was at 75%. I just weighed the charge into circuit 2 about two months ago due to oil problems. I will check the charge in circuit 2, but I don't believe this is the problem, I have a full sight glass, but will check sub-cooling and super heat to be sure.

I appreciate your response.

Grizzly
23-05-2013, 06:14 AM
Grizzly,

Thanks for your response.

The liquid injection is for compressor cooling, which gets hot due to the oil. All three compressors were running at the time; circuits 1 and 3 were at 50% and circuit 2 was at 75%. I just weighed the charge into circuit 2 about two months ago due to oil problems. I will check the charge in circuit 2, but I don't believe this is the problem, I have a full sight glass, but will check sub-cooling and super heat to be sure.

I appreciate your response.
Don't forget the viking he has contributed as well and obviously made a good guess.
Because you yourself had eliminated the charge as being a problem, although "we" did not know that!
(The compressor gets hot because of what it's doing.IE Compressing gasses.
The oil maintains the seals and bearings and absorbs heat as well.) Although i think you knew that?
You just did not word it so well!

Hopefully there is someone here that knows these comps better than me, (not hard) that is willing to help.
If what you are saying is fact, how come none of the solenoids were energised?
Grizzly

CommercialHvac
24-05-2013, 02:44 PM
Grizzly,

I do appreciate your help, what was throwing me off in trouble shooting the problem was in the McQuay literature, when it stated that the liquid injection was energized at start up, but that was all the information they gave in the literature that I have, so it led me to believe that they stayed energized all the time. Well, I finally was able to catch up with a McQuay Tech on the phone and he pointed out that liquid injection does not stay on continuously, it shuts off after initial start up and will not come back on unless oil pressure drops or discharge temperature reaches 165 degrees F. He said I need to check loader solenoid valves to make sure they are energizing. EXV will load up according to what control is calling for and display will indicate that load percentage but compressor actually might be starving for refrigerant.

Grizzly
24-05-2013, 07:09 PM
Good to know and glad you are getting somewhere.
Thanks for the update.
Interesting info!
Grizzly