A/C sometimes not cold when idling

[Acobrajet321]

2011 Yukon XL. A/C works great while traveling down highway, very cold. However, when sitting in parking lot or in line at drive through air vent temp climbs from a frosty 38-42 to 70-75. Not fun in traffic jams at 95 degrees, but also not a failure. Had the charge tested and system leak tested at shop. 3lbs, no leaks. Compressor pressures were in range. Used scan tool to activate low and high fans. Both work when activated. Replaced relays anyways, still work. Noticed that when idling in driveway in 93 degrees heat the high pressure climbs to just about 200 and kicks off. Drops to 175-180psi and kicks back on, kicks off again at 200psi, about 10 seconds later. Air temp from front vents cools down during the short pressurized cycle. It’s like it’s just not running long enough. I wish I could ‘tell’ the compressor to stay on longer. I think that would solve it. I even activated high speed fans with scan tool to see if it would help. Only minor improvement, don’t think it’s fan related. Is there a reset procedure or could the module be sending a signal to kick off too soon? Bad module? Something else? Engine coolant temp sensor was replaced last year. Says engine temp 196-200 while idling. Confused as to why system is turning off before it builds enough pressure. Did notice RPms dropping a little below 600. Could it be RPM related? Thanks for any help.

 

[OR VietVet]

More Information for GM GENUINE 155687

May want to consider this.

Welcome to the forum from Oregon

 

[OR VietVet]

You really should post this question in the correct section of 2007 to 2014.

 

[CMoore711]

This may or may not be related to your issue or experience, but is somewhat similar…

The A/C is acting up in my wife’s ‘13 Escalade ESV. Had some recent service/tests done; No leaks, condenser works fine, compressor was fine, evapped 2.8lbs. of refrigerant to replace with 3 lbs. of refrigerant. Get in the truck A/C turns on blows cold, thought we were good.

Fast forward a week later my wife says it’s still not working right, it goes from blowing cold to blowing ambient outside air temp at random. That’s odd are you sure? So we traded vehicles for a day and sure enough during my drive at random A/C would go from cold to ambient air, then back to cold. I can’t duplicate it, it’s while going down the road driving, randomly in traffic, or at idle. But not a specific condition.

Come to find out there’s a magnetic clutch in the compressor that’s failing intermittently. The compressor has power, has good ground, but just randomly disengages the internal clutch and stops the A/C pressure and starts to blow ambient air through the system and not cold air. Then randomly re-engages to work as it should.

New A/C compressor ordered.

Part #25940200 about $280 +/- shipped from various GM parts sites. Surprising Rockauto didn’t offer an OEM option only aftermarket. Dealer wanted $475 for the part plus $1,000 for labor.

 

[swathdiver]

2011 Yukon XL. A/C works great while traveling down highway, very cold. However, when sitting in parking lot or in line at drive through air vent temp climbs from a frosty 38-42 to 70-75. Not fun in traffic jams at 95 degrees, but also not a failure. Had the charge tested and system leak tested at shop. 3lbs, no leaks. Compressor pressures were in range. Used scan tool to activate low and high fans. Both work when activated. Replaced relays anyways, still work. Noticed that when idling in driveway in 93 degrees heat the high pressure climbs to just about 200 and kicks off. Drops to 175-180psi and kicks back on, kicks off again at 200psi, about 10 seconds later. Air temp from front vents cools down during the short pressurized cycle. It’s like it’s just not running long enough. I wish I could ‘tell’ the compressor to stay on longer. I think that would solve it. I even activated high speed fans with scan tool to see if it would help. Only minor improvement, don’t think it’s fan related. Is there a reset procedure or could the module be sending a signal to kick off too soon? Bad module? Something else? Engine coolant temp sensor was replaced last year. Says engine temp 196-200 while idling. Confused as to why system is turning off before it builds enough pressure. Did notice RPms dropping a little below 600. Could it be RPM related? Thanks for any help.

If your clutch cycling on and off the system is low on refrigerant regardless of what someone told you. Do you have a manifold and vacuum pump? If yours were mine, I would evacuate the system, replace the service port, tighten the schrader valves and replace the covers. Then would put the vacuum pump on the truck to first test for a leak and then to remove any moisture for about an hour. Then I would add four 12 ounce cans of refrigerant and keep a 5th on the shelf for a spare.

Doubt idle has anything to do with it, they are set to idle at around 500 or so.

 

[RED TAHOE LS]

With traffic/humidity/low air flow and rpm's, leave on MAX , lower blower speed to second notch, slowing airflow allows evaporator to cool better. You have all the engine heat plus firewall heat and none of these on the rear ac. once the initial cool down, lo blow will give you 40 degrees @ the center outlet. How do i know, because mine does it, highest it ever gets in bumper to bumper is 50 degrees above 90's outside.
226k miles, all original including engine/ac complete........good luck.

 

[Acobrajet321]

I ended up borrowing a sniffer and spent a good 3.5 hours 'sniffing' the whole system from rear to the front looking for a leak. Found nothing initially. Then I turned the front system off (rear on) and picked up a very faint leak coming from center dash vents. Dang it..... Very Very small leak in front evaporator. Was leaking slowly enough that it would take a few weeks before it was low enough in a 3.5 lb system to not have pressure at idle, but still had enough to cool while cruising. I'm sure if I had went longer it would have eventually stopped working all together for lack of charge. Got a quote of $2900 at an Indy shop. It took me a full weeekend to do at home. Had the shop draw down Friday afternoon, finished around 9:30 sunday night. I took it back for a leak test/recharge Monday. A big PITA project to say the least, but doable. It's held a full charge for 7 months now. Been working just fine for the past 2 weeks now that temps are in the 80s again.