Guys, three times to the dealer on this one. I'm pretty fluent in a/c stuff. So here is what I have.

07.5 LMM with 19K on it.

At 70 mph (about 1800 rpm) the temp of the air coming out of my vents get warmer then cooler again. Like the compressor is cycling. Grille is not plugged.

Had a buddy keep the rpm's at about 2000 and sure enough the compressor is cycling about 7 seconds on then 3 seconds off.

First trip to the dealer found no leaks but freon supposedly a 1/2 lb. low. Second trip found nothing wrong. Third trip found the cap on the low side port leaking. Supposedly they changed the cap, evacuated and refilled. When I picked it up it still cycled at 2000 then after a minute stayed engaged for over a minute. So I figured it was fixed.

I figure the 134 port under that leaking cap is probably leaking itself.

My question is, what should the pressures be, at what humidity and temp AND should the reading be taken at 2000 rpm. My '96 tahoe Helms manual gave a chart and stated to take readings at 2000.

Any help would be greatly appreciated. Thanks in advance guys!!!!

I would reference the chart you have for the Tahoe. They are both cycling clutch systems; should get you pretty close.

I figure the chart would be close, but cycling so frequently even at highway speeds? Its real good around town (because the clutch is constantly engaged) but on the highway I lose a little temp. Dealer told me it does that so it doesnt freeze up on the highway. I still think its low on 134 and the dealer didnt take a reading at 2000 rpm.

Any other ideas? Thanks again.

Guys, three times to the dealer on this one. I'm pretty fluent in a/c stuff. So here is what I have.

07.5 LMM with 19K on it.

At 70 mph (about 1800 rpm) the temp of the air coming out of my vents get warmer then cooler again. Like the compressor is cycling. Grille is not plugged.

Had a buddy keep the rpm's at about 2000 and sure enough the compressor is cycling about 7 seconds on then 3 seconds off.

First trip to the dealer found no leaks but freon supposedly a 1/2 lb. low. Second trip found nothing wrong. Third trip found the cap on the low side port leaking. Supposedly they changed the cap, evacuated and refilled. When I picked it up it still cycled at 2000 then after a minute stayed engaged for over a minute. So I figured it was fixed.

I figure the 134 port under that leaking cap is probably leaking itself.

My question is, what should the pressures be, at what humidity and temp AND should the reading be taken at 2000 rpm. My '96 tahoe Helms manual gave a chart and stated to take readings at 2000.

Any help would be greatly appreciated. Thanks in advance guys!!!!


I'm having the same problem on my '09 right now. I'm going to get a gauge in the morning to check the low side pressure. It's ok around town , but it's cycling on/off on the highway only getting cold for a few sec or so then blowing warm. When it's over 105 daily, that is unacceptable. My old truck was like a freezer, even in the summer heat, and the a/c in the little Malibu is ice cold. At the vent my truck says 52F at idle and the Malibu is 40F, but the highway is where the problem is. I think my pressure is dropping at highway rpm, and I'm low on 134.

I'm gunna check it all out in the morning, I've got about 3500 miles of highway over the next two weeks so this needs to be fixed.

Went and got one of those refill bottles with a gauge inline. It was 35 at idle and 25 at 2000rpm. It was on 7 seconds at 2K rpm, then off 3 seconds exactly like yours is. I added a little and it cycled every 12 seconds but was still about 25 psi. I added a bunch more and now it is about 30 psi at 2K rpm, stays at 40F now, and doesn't constantly cycle anymore. Idle temp also dropped about 5 degrees. Outside temp was around 100F. I'm happy now, but I may put a shut off valve on the heateur line going into the cab.

Hope this helps you.

Same here!! I just checked mine. My low side does have some green die around the port after I took the "new" cap off. My readings are the same 35 @ idle and 25 @ 2000. I think I'll toss a can in. I'm willing to bet the dealer took the readings at idle instead of 2000 (cruising speed).

If anyone has any other thoughts please post!!! Thanks