What causes a fluctuating high head pressure on an A/C unit? (See details)?

Question

I'm servicing an older system (12-15 yrs)
The system isn't cooling properly
When I put the gauges on it, the suction
Pressure is pretty constant at
80 but the head Pressure changes wildly
Between 225 - 375, the liquid line is
Ambient to the touch, and the suction
Line is cold and sweating, the outside temp is 80° F. I have a feeling the rings
Of the compressor pistons may be failing,
For any ideas I would be greatly thankful.

Answer 1

I'm assuming this is an R22 system. The problem can be a few things but you did not provide enough information to answer the question. First, the 80 lb suction pressure may or may not be high. What is the indoor ambient temperature? 225-375 lb head pressure seems a bit excessive for an 80 deg day. I assume the condenser coil is clean. If it isn't, then clean it and recheck your readings. My suspicion is that the unit is overcharged or there are noncondensibles in the system. Is the metering device a piston or a TXV? If it is a piston, check the charge using the superheat method. "Beer can cold" suction line is NOT an acceptable charging technique. You have to determine the actual superheat and compare it to the target superheat. If actual superheat is lower than target superheat, remove charge to raise superheat until it is within +/- 5 deg of target. If the system has a TXV, you will need to use the subcooling method to check the charge. Compare actual subcooling to the system's design subcooling. If actual subcooling is higher than the design subcooling, remove charge until the actual subcooling is within +/- 3 deg of the system's design subcooling. If you have absolutely no idea what I've been talking about, its time for you to call a professional.

Answer 2

Head Pressure Causes

Answer 3

Need to know:

Type of meternig device, superheat, subcooling, Delta T, compressor amps.

I suspect an overcharge, non-condensibles in the lines, faulty gages, too.

I'd be expecting to see low discharge/high suction on a bad compressor.

You'll have to evacuate the system and recharge it to be sure.

Answer 4

Did you ever hear the story about the installer who's vacuum pump broke and because he never had a micron gage he never pulled a vacuum on the system ? Noncondensables we call that. Wrong Refrigerant ? Contaminated refrigerant ? Mixed refrigerant? Condenser fan not operating properly? Over charge? Dirty condenser coil? TXV stuck wide open? Forgot to install orifice? Too much oil in system? By the way, restricted liquid line will cause high side to go down not up. OK , 10 simple ideas to get you started.

Answer 5

No, no.

I'm no A/C repairman, but 375 on the disch end says good rings (if it has rings?). Possibly even overcharge?



I would look for a big ball of ice in the air side of the inside coils, or a nearly plugged air flow around the coils.

Answer 6

Bad compressor or components in it. Time to R^R the unit.