cashup88

I have a 99 Silverado 1500 LS. A couple months ago my AC started blowing hot so I attempted to put a new can of refrigerant in the system but the AC would not engage. (I now know it was because the system was completely empty). Since then I have replaced the compressor/clutch, condenser, accumulator, oriface, and low pressure switch. When I hook up the dual hose manifold the low pressure side continues to build as the compressor cycles on and off (I saw it start getting close to 100 PSI before I closed the valves). The high pressure side would jump between 50-200 as the compressor cycled on and off but would not hold pressure if the compressor stayed off. I’ve used dye and a vacuum to test for leaks and have found none. My compressor still won’t stay engaged and my AC is still hot.

chem_man

Did you add any PAG 150 oil to the new compressor before installing it? If yes, how much? Also, how much (in weight) R134a did you add to the system? Did you flush the condenser with AC flush?

Oil capacity for the 99 Silverado AC system is 8 ounces (3 in the compressor, 5 in the accumulator), and the weight of R134a that the system holds is 32 ounces.

R134a systems are filled by weight. Do not go by pressures on the manifold gauges.

When you initially start putting the R134a into the system it's best to place a jumper (like a paperclip) into the connector that goes to the low pressure switch on the accumulator so the compressor will stay engaged. Once you get the correct amount of R-134a into the system, remove the jumper and plug the electrical connector into the low pressure switch. The compressor should stay engaged most of the time.

cashup88

When I installed the new compressor I added about 2 oz of oil because that is about what I got out. When I replaced the accumulator I put about 5 in it because that’s what I got out. I did not flush the new condenser. I’ve put almost 12 oz of refrigerant into it but the high side pressure is not changing while the low pressure side is rising to almost double what it should be.

chem_man

OK on the oil and not flushing the condenser. Did you jumper the low pressure switch when you added the 12 oz of R134a?

Just as an FYI, when the AC compressor engages, the low side pressure will drop and the high side pressure will increase. When the compressor dis-engages, the low side pressure can easily go to 100 psi or higher, and the high side pressure will drop. If the compressor stays disengaged long enough, the low and high side pressures will ultimately equalize to the same pressure.

Exactly what were your low and high side pressures when the compressor was engaged, and what were they when the compressor dis-engaged?

How did the old orifice tube look when you removed it? Was it clean or was it dirty? If it was dirty, then you really should flush the condenser to get whatever junk is in there out.

Do you know if your old compressor had a catastrophic failure? If it did then chances are the condenser is full of crap and it will be almost impossible to get it all out and all the AC pros I have run into would strongly recommend replacing the condenser. These newer condensers have very tiny passages compared to the condensers of the early 90s condensers.

cashup88

When I bypassed the low pressure switch and forced the compressor to run it started taking refrigerant. I put about 32 oz. of R134 in and the high side was reading 225 and low side about 50. I live in AZ and it’s always hot so I figured that’s why they are a little higher.

The old oriface was dirty and nasty so I changed the condenser that same day.

now that the compressor is staying engaged the system is running well and cool. Thanks for the trick.

chem_man

OK on changing the condenser as well. Yes, living in Arizona with higher temperatures will lead to higher low side and high side pressures. Your pressures of 50 & 255 are reasonable and not out of line.

You are quite welcome!