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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 7599
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a walk in cooler that wont cool down below 36.It had

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I have a walk in cooler that wont cool down below 36.It had a leak that I repaired then recharged.Now it won't ull down below 24 lbs and the high side is 85 lbs.
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: 24 hours
JA: Do you plan on doing the work yourself?
Customer: yes
JA: Anything else we should know to help you best?
Customer: I put in a new expansion valve think that maybe I damaged it when I fixed the leak and it was flooding the system. I also fixed a kink in the suction line by the valve at the same time.

Hello, Those pressures do not fit any known refrigerant.. we need to address that first. Tell me what refrigerant you are using, and if you vapor charged the system or liquid charged it.

I need to know what the air temperature around the condensing unit is when you get the 85 psig pressure reading. (no refrigerant reads that low on head pressure unless it is below 30F around the condenser when the reading is taken).

I am able to train you on all this if you wish.

Customer: replied 1 month ago.
I'm using 134A, I vapor charged the system ,The room temp is about 65 degrees F

Thanks, ***** ***** pressure for that system should be 118 psig, given the fact of a 36F box, the suction pressure should be considerably lower than 24 psig...into the 15 psig range.

I would expect these results with a grossly over sized evaporator and condensing unit... is this a new system that you have just installed?

Next I need you to tell me if the compressor body is cool or sweating.

We can go from there.

Customer: replied 1 month ago.
The system is very old and has been running fine right up to the point of the leak.The compressor is hot to the touch I'd say normal.No sweating.The HP line is hot going into the condenser and cool coming out.The LP line sweats by the evaporator ,but not by the compressor like it used to.There was a kink in the LP line behind the evaporator that I repaired while everything was apart.It had been kinked for years and the system ran fine.I have never seen a problem like this and have been doing my own work for about 40 years.
Customer: replied 1 month ago.
I tried adjusting the expansion valve 3 turns in pressures now 90/20.I'm wondering if the kink in the LP line that I repaired has something to do with this problem.

Hello, about 50 years ago when I was still new to the business we had an AC suction line, 7/8" kinked flat (completely kinked) suction was 55 psig, when we removed the kink suction was only 5 psig higher (r-22 60 psig),

The kink in your case would have had a minimal negative effect.

Due to the high suction pressure and low head pressure I suspect the compressor valves are going bad, do a pump down test on the system.

If the valves in the compressor are bad, it will not hold the vacuum when you turn the compressor off, and the suction pressure will rise to match the head pressure (compressor off) and... you will hear a gushing sound as hot gas leaks back through the

compressor valve plate into the suction that will then suddenly get very warm.

Here is a war story for you:

About 40 years ago I found a leak at a 1-1/8" tee in a suction line between two coils, it had never been soldered... it was a very old system (prior to R12, used that flammable refrigerant, forgot name)... it had been running that way, leak free for the previous 20 or 30 years... the ridge that a tube cutter makes on the outside of the tube acted as the seal.

Customer: replied 1 month ago.
I shut off the HP line at the compressor and pumped it down.It took about 3 minutes and I could only get the low side down to about 10 psi and the high to about 50 psi.I shut the compressor off.I didn't hear any gushing sounds.The low side line seemed to get a little warm,but the high side line got cold,enough so condensation was forming on the dryer by the compressor.The pressures held the same on my gauges for about 4 minutes -until, I released the pumpdown.
Customer: replied 1 month ago.
I seated the ssv and let the compressor draw down for 2 minutes or so. It only got down to 8 psi.and that took about 1 minute.I never had a compressor long enough to have bad valves and this one is only about 3 years old.Do you think they are bad?

Thanks, ***** ***** compressor only pumped down to 8 or 10 psig (and your gauges are properly set to zero when not connected) then the compressor suction valves are going bad (depending on the type of compressor)...all compressors should be able to pump down to 0 psig suction... the older piston types routinely pump down to 20 inches of mercury on the vacuum end of the low side gauge. (Scrolls will pump down to below zero psig,into a vacuum as well, but should not be pumped down below zero).

If the low side tube at the compressor warmed up noticeably after the pump down, that points to slightly leaking intermal compressor discharge valves as well.

The pressures you gave at the outset 24psig and 85 psig also point heavily to a compressor with leaking valves.

Phil and other HVAC Specialists are ready to help you
Customer: replied 1 month ago.
Thank you for the help.I put a new compressor in and it runs fine.I did the pump down test but it didn't bleed back,but it also would not pump down below 10lbs.I figured the compressor was weak.

That is right, and you proved it with the new compressor.

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