Heat blows when ac is on?

[Paytonz71]

Just started having problems yesterday. Heat blows out vents when ac is on! Someone please help!

 

[95C1500]

Could be low on refrigerant which also means you have a leak in the AC system. Get some gauges and check the system to be sure.

 

[east302]

Assuming your system is charged...

The temperature door actuator adjusts to divert air to or away from heater core based on where the dial is on the hvac panel. Your damper may be stuck due to a linkage problem, bad actuator or bad hvac unit. It's #3 in this diagram, kind of behind the ashtray if I remember right...

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Look up at it and there should be a small dial with a notch in it. See post #3 in this link for a picture of it.

http://www.gmt400.com/forum/showthr...e-right-spot-Weird-thumping-sound-interior-AC

See if it turns in response to you turning the temperature dial on the panel.

 

[Kyle97GMC]

I had the same exact problem and it was the AC control module and switch. $25 for both of them and about two minutes of splicing wires and it fixed the problem