2003 Yukon 5.3L ....HVAC kills the car at idle....Runs good when HVAC is off
I suspect faulty/dirty idle air control valve. When the ac comes on the control valve is suppose to idle the engine up to compensate for the added load of the ac compressor.
I agree with dandy on the IAC, check the trouble codes, there could be something in memory, clean the throttle body and the IAC, if the problem still exists then you should check the A/C compressor and make sure it still turns and is not locked up. You could also try unplugging the A/C compressor and then turn on the HVAC to see if it kills the engine. If the engine still shuts down with the compressor unplugged then you may have a signal problem to or from the ECM and that will require further system testing.
It Also Happens When The Just The Heat Is On and No A/C
Your idle should adjust anytime your ac compressor comes on. Your ac compressor also runs when the defrost setting is selected. Try this. With everything off and truck idling. Turn your steering wheel hard to the left then hard to the right. Your idle should go up when power steering pump is working. If your idle remains the same when trying this I suspect idle air control valve is not operating properly and needs to be cleaned or replaced.
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