A/C does not cool below 2000 rpms

[mukdog13]

'04 LS. Whether idling in park or driving, if below 2000 rpms, the A/C will not cool. Once I get it above 2000 rpms (~2100),you can feel the air starting to cool. I connected a gauge to the low side ( i know that is not a definitive indicator) and it read fine. The car does not overheat and the fan does kick on. When sitting at idle in park, i got underneath to take a look at the compressor and the clutch for the compressor cycles. Any help would be greatly appreciated.

 

[mukdog13]

3.0 V6 in case you were wondering.

 

[joegr]

Normally, your symptoms indicate a bad compressor. A check of the high side pressure would help to confirm this. I have heard that there's a part of the compressor that can be replaced to fix this, but most people just replace the whole compressor.

It seems strange to me that the clutch is cycling. The LS will only turn the clutch off if the evaporator temperature gets down to freezing. I wouldn't expect to be happening if it isn't cooling very well. You might check the evaporator temperature sensor, but I don't know why or how it would relate to engine speed.

 

[Kumba]

If the clutch is slipping you might be able to put a few extra shims in it. I'm of the same mind as everyone else, if I have to work on the compressor I would prefer to replace it all with my best guess reman.

 

[joegr]

If the clutch is slipping you might be able to put a few extra shims in it. I'm of the same mind as everyone else, if I have to work on the compressor I would prefer to replace it all with my best guess reman.

Just to be clear here: I wasn't thinking of a slipping clutch. He should be able to hear that, and he should check on that. That fault that I was thinking of is one internal to the compressor. There are some valves inside that can wear out or fail such that the compressor no longer pumps enough refrigerant at lower RPMs to work correctly. This is not an issue specific to the LS, but rather is something that is known to sometimes (pretty rarely) happen to any scroll type automotive compressor.

 

[86markviilsc]

Could be failing or sticking expansion valve. If it's stuck open, it's only getting enough flow to function somewhat with the higher RPM's.

 

[joegr]

Could be failing or sticking expansion valve. If it's stuck open, it's only getting enough flow to function somewhat with the higher RPM's.

Yes, that's possible. I'd pray for it to be the compressor instead. I've seen this symptom on a couple of cars before and it was the compressor.

 

[Broseph]

Yes, that's possible. I'd pray for it to be the compressor instead. I've seen this symptom on a couple of cars before and it was the compressor.

I had similar symptoms before my a/c quite altogether. My question that I think is relevant for other members is I have a new compressor and THEY recommend replacing a/c drier (duh) and expansion valve (ugh). Would i be able to just do the compressor and if the prblem persists, I know its the expansion valve, or would this possibly ruin the new compressor if the valve is shot?

When I first had the "cold at high rpms" issue, I took it to a mechanic who said he unplugged the engine fan and the condensor pressure shot up real high leading him to believe the compressor was fine and it was the expansion valve. He topped off the R134 and the problem was better, but it was still there. Is this a correct diagnosis?

Oh, it's an 02 3.9 btw

 

[joegr]

It is generally recommended to replace the expansion valve when a compressor fails because the when the compressor failed, it may have contaminated the system with little bits of itself. It's easier to flush the system if the expansion valve is removed, and the valve may be clogged by the debris from the compressor. Also, it's not a bad idea since they are relatively cheap and it might be the valve that was bad anyway. The catch to all of this is that the whole dash has to come out on the LS to replace the valve.
I'd have it flushed as much as possible, replace the dryer, and the compressor, and see what happens. If the valve is stuck closed (instead of contaminated), then it won't do any harm to the new compressor.

As far as his method of diagnosis, it's not foolproof, but maybe.