AC shuts down when engine bay temps increase

[02YukDen]

Hi Folks,

I am new to the forum and hope someone can help me with my AC problem.

I have a 2002 Yukon Denali with 110,000 miles. Everything is bone stock.

The Symptoms:

When first started on a cool day (under 75 degrees) the AC will turn on and run normally untill the vehicle either sits idle for an extended period of time, or driving slow in traffic / constant stopping from a series of stop lights at which point it turns itself off.

If I pick up speed and get some air flow through the engine bay, at some point the AC miraculously turns itself back on.

On really hot days (85 plus), the AC won't even turn on if I walk over to the car and start it up after sitting idle for several hours....or even all night. If I however get on the highway and get cruising for a long enough period of time, the AC will turn itself on.

This seems to be a temperature related phenomenon and I can't quite figure out where to start. I have switched the relay with one that I know is working with no change.

Anyone know what might cause the AC system to respond negatively to very warm temperatures, then correct itself with enough convection passing through from high speed driving?

My thought is to replace the AC Compressor, but this is an expensive step to find that the existing one is ok.......Help!

FWIW, I owned the vehicle for almost two years before the problem developed.

Many thanks!

 

[sumo]

there are few things that determine ac on and off. One factor could be a low charge. you can try a recharge and a dye added to see if there is a leak somewhere. Another factor is engine temp as stated. make sure your coolant is topped off. If that is ok, it could be a bad switch. If the engine temp reads over a certian degree it going to shut off the compressor until readings are within specified range then it will allow compressor to cycle on.

 

[02YukDen]

there are few things that determine ac on and off. One factor could be a low charge. you can try a recharge and a dye added to see if there is a leak somewhere. Another factor is engine temp as stated. make sure your coolant is topped off. If that is ok, it could be a bad switch. If the engine temp reads over a certian degree it going to shut off the compressor until readings are within specified range then it will allow compressor to cycle on.

Sumo,

Thank you for the response........this 100 degree weather and two young kids makes driving anywhere miserable.....

The coolant is ok, and I checked the charge without the compressor running (The AC had shut itself down) and it showed very high pressure on the gauge. Does the charge need to be checked with the compressor running to provide accurate results?

Also, switch you refer to, where do I find this, and how do I check for proper function? Or is the switch cheap and easy to change out?

Thanks again!

 

[sumo]

its the ac low pressure sw on the accumulator near the low pressure port. think the wires are blue and green if i remember correctly. you can jump that connector and see if your compressor stays on indicating low charge or bad switch. If your not familar with ac work, id highly recommend taking to a ac expert as it will require you to Evac the refrigerant in order to replace that switch.

 

[02YukDen]

I jumped that switch (Low pressure on accumulator), the high pressure switch located on the compressor, and another switch I found on a line coming from the Condenser with no luck on any of them. None triggered the compressor.

Also, I read that these switches have schrader valves which prevent one from having to discharge the system for a switch replacement. You mentioned that replecement would require a complete system recharge.

I guess I need to check the refrigerant level again. The problem is without an engaging compressor, I can't check the pressure.....which is crazy, because if the level is low the compressor won't run, and you can't fill up the system if the compressor doesn't run. Kind of like saying "you need to turn the faucet on, but you can't turn the faucet on unless water is coming out of the tap.........."

Just a tad frustrated here, and with 95+ degree weather I can't get my compressor to run so I can check my level again.

Can anyone recommend a good HONEST AC mechanic in the Lower Bucks County area just north of Philly?

 

[sumo]

weird even though a low charge you should be able to jump it. Maybe compressor going?

 

[02YukDen]

weird even though a low charge you should be able to jump it. Maybe compressor going?

I hope not.......that seems like it would be a tad expensive. Days like today (95+ degrees) I can't even get the compressor to kick on when cruising the highway for 30 minutes. If it were 80-85 degrees it would kick on after about 10 minutes of highway driving. Furthermore, if I got up in the morning after an evening of temperature drop the AC would probably come on a soon as the car was started.

Very strange. The problem seems to be very consistently sensitive to ambient temperature inside the engine bay. An increase in temperature will cause an increase in system pressure. Is it possible for my system to have randomly developed an over pressure problem even after a couple summers of driving without incident?

I agree the paper clip should have jumped at least one of the three switches I checked. I guess that must logically put the next focus directly on the compressor itself.

Thanks again for your help Sumo.

 

[02YukDen]

OK.....had a chance to check the refrigerant level with the compressor running. Exactly where it should be per the gauge on the refill canister.

Bought a new low pressure cycle switch (attached to accumulator) and just installed it. Car started, AC turned on, and then turned back off about 5 minutes later. Car was sitting idle in the driveway the whole time. I don't know if it was a coincidence, but the AC turned off just as I adjusted the climate control dial on control panel to a lower temperature. Could my actual climate control dash mounted control panel be bad and cause this to happen?

Thanks again for your help with this.

 

[JoeOmerta]

Does the vehicle have a mechanical cooling fan? It could be the fan clutch going bad. It's a cheap fix.

Test procedures...
1) start car and let idle
2) wait till a/c no longer blows cold
3) spray condenser with cold water
4) check for change in a/c temperature

Test 2
put a piece of paper on the front of the condenser, the fan should hold it there by suction at idle very easily

 

[fatnlowtahoe504]

is your vehicle engine running very hot???? if so that will make the A/C run hot as well, if it is running hot check your thermostat and or water bump...my thermostat went out and my truck was about to overheat and my air was coming out extremely hot then all of a sudden i noticed my temp was stupid high and had a coolant temp check light message come on the little screen......so that can also be a factor