2003 GMC Yukon xl with Climate Control A/C. OK, first let me say this has been happening on my Yukon for at least 3 years. Yes, I know that is a LONG time to have a problem with an A/C unit in Texas! I was fortunate? enough to find out how to cope with this immediately, so I guess it wasn't a pressing issue. The drivers side a/c will suddenly begin to blow hot air, just as if you turned on the heater. You can turn off the A/C, work any of the controls anyway you want etc and when the unit is turned back on, it will still blow hot air from the drivers side ONLY. BUT if you turn off the ignition and restart the car, then INVARIABLY it will resume normal operation. It may then work for 500 miles, or 60 seconds before it messed up again, and the ignition must be shut off and restarted for it to work normally again. I did have it in the shop about 2 years ago, and they replaced the acuator located under the dash on the rt middle. Didn't help at all. I have decided (based on NO mechanical ability) that this problem has to be either computer related or electrical in nature. Either the computer is malfunctioning periodically and the off/on of the ignition "reboots" it, or the initial surge of electricity is sufficient to close some circuit which is stuck closed. I should also mention that I have also for several years had a problem with my alternator, oil pressure gauges reading wildly inaccurately all the time. I am getting ready to take it into the dealer to have this fixed? I am hoping for some good info from this forum BEFORE I take it in. Thanks for reading this long post. Any questions just ask. Any thoughts appreciated.