Heat isnt working on my 94 GMC Suburban. Changed thermostat. I have a "ticking" coming from under dash on pass. side when I hit the max button on controls. It also "ticks" when car is turned on/off.
Blower shaft bushings dry or need replaced. runs with key power and speed increases when blower speeds are selected. could be. Max would actuate fresh/recirc door above it. If your temp. blend door does not move, and is turned away from heat setting. look at the control for it. if you have a blend door actuator, it could be stuck. Loss of vacuum would give defrost all the time. so when you say heat isn't working ? what does that mean ? no air flow ? cold airflow ? airflow to the windshield only ? seems like you best get it looked at. that would save you money and time. Or you could do some checks and more fully describe after reading this.
Air flow comes out right on each setting; defrost, dash vents, floor vents. The air temp itself does not blow hot on any setting.
Then if your coolant is full, and your heater hoses both feel warm, You must have a temp. blend door stuck not allowing the air to pass over the heater before it leaves the case. it could be obstructed, stuck, or the actuator could be out of position or out of range.
What's the best way to get at the blend door?
www.youtube.com/watch?v=Ow0OOfIFtlU --- this should give you a basic idea... Just when you get in there replace the one that's ticking cause it's stripped out probably.
Thanks for the help guys. Found a video from someone that had the same problem and he shows how to fix it.
There's an acutator behind the glove box that needs replacing feel it when you hear it under dash
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