JoeBlow

I neglected to check the heat on my 2001 before I bought it last week. I checked the AIR you can be sure.

So, today I turned on the heat and things got nice and hot. But then, it would not get UNhot. It was HOT.

When I got home I shut down the truck and checked the fuses. There are several which are labeled HVAC or HEAT. All were fine.

So, I tossed the yot in the water and drank a mess of beer. Several hours later I fired up the truck and guess what? The heat was OFF.

What could cause this? The temp selector feels like a rheostat and doesn't seem to be connected to a cable. Does it drive an airflow door of does it drive a water valve?

I am going to pull the factory radio soon and install an aftermarket unit. Is there anything I can check when the radio is OUT and I have access to the back of the heater switches?

Doug Roberts

I have a 99 and the controls module takes care of all of it ???
If bad switch metallic plate could be broke and stuck

Peter M

Cant hurt to replace your relays. I have seen them fail in the open position. and when circuits get hot things happen...

Doug Roberts

True I took off my controler and used a meter that's free

oldchevy

Sounds like your blend door actuator is sticking. The use an electric motor to do the switching. It is almost all plastic and the gears tend to break with age. You have to remove a panel under the glove box to get to it.

adam86107

If it was the blend door actuator your should be able to turn the heat off just not control the temperature.

oldchevy

The blend door actuator controls the the temperature. It changes from heat to cold and all the positions in between.

JoeBlow

so if the heat returned to the off position after shutting down the truck and walking away.....

sounds like the door moves. if it moves, the gears must be ok.

adam86107

Yeah but it can get stuck closed on the cold side and only allow hot air. Mine is messed up on my driver side in my 04 since it has two blend doors one for driver and one for passenger. I can be driving down the road with the a/c on and the driver side blend door will shut the cold side off and I'll be getting crazy hot air while the passenger still has nice cold air. The only way for me to reset it is to pull over and shut the truck off and start it back up and everything is fine again. This will not affect the ability turn the heat off though you just can't control the temperature.

JoeBlow

Well, it did it again today.

I am going to guess that either the door is sticking open or that the rheostat which controls it is defective.

Has anyone accessed the door? Is it impossible to get to? I can't imagine that it requires lube. My guess is that it's busted.

I don't want to tear into this thing unless I know what is actually wrong. I also don't want to spend the money on a new switch module if it's the door.

Had anyone fixed this issue on their truck?