Suddenly my heat has stopped working. Luckily it's the end of the season but that also kills my defogger and it gets pretty wet here in gloomy western Washington. The car sat for three days last week and now the system comes on and blows but just cool air no matter what temp and blower level. The AC hasn't worked for 4 years but I've always had heat/defrost. The car is a '91 OCC. Both heater hoses are hot past the HCV into and out of the core. I actually replaced the HCV three years ago because of a leak and have had zero problems until now. I've disconnected the battery and let the system reset, that usually fixed it when this happened in the past but has not worked this time. I've actually tried four times. The water pump, fan clutch, and thermostat were replaced around the same time as the HCV. (195 degree thermostat) She warms up normal, heats the gauge to 195 and drops to 140-150 after five to eight minutes of driving. I planned to dump the old coolant and flush the system this weekend anyway but this seems more controller related. It is the automatic climate control system. Any suggestions of what to check next?

 

somewhere there is a heater control on the heater hose, maybe the cable popped off or if its electric the solenoid maybe quit

 

If your AC worked I'd tell you to check if you only had cooling from one side of the dash. There's an air door in the plenum that controls heat/AC between the driver's side and passenger's side of the dash. It went out in my 96 98 and I only had heat from one side. In my 98 the actuator sat on top of the plenum behind the glovebox.

 

I finally had a chance to try some fixes. I replaced the heater valve because it was the easiest to get to and voila, heat. I just replaced the leaking original one three years ago. This one was no where near as good but was GM genuine. Guess they don't make them like they used to.

 

Good to know you got it fixed. What part number was the valve you replaced? Did you just get it from the parts store?

 

GM Genuine 15-5342 for the first replacement and the one I put in yesterday.
I got this one on Amazon and the last one on RockAuto.

 

Awesome.👍