help with 1999 sierra

[shogun]

I have a 1999 gmc sierra that has no heat to the vents or defrost. Both hoses to the heater core are hot, and I took out my temperature control module and tried another working one but to no avail. The only air coming through the vents is cold all the time, not even a hint of warm air. Could it be a blend door actuator? Any help is greatly appreciated especially with lows in the 20's.

 

Thanks

 

Josh

[GM-Tech]

Could be the temp door actuator or a stuck door. Is this manual or auto a/c? Dual zone or not?

 

The temp actuator is located on the bottom of the case, almost in the center. You could take this off and see if you can rotate the shaft for the door by hand. This will tell you if the door is stuck, plus you can see if this gives you heat.

 

DO NOT turn the key on or try to operate the actuator when it is not mounted to the case.

[shogun]

By manual a/c I assume you mean that I turn it by hand. It is the three switch control module with the first switch controlling the fan speed, the middle switch controlling the temperature, and the third switch adjusting the location (defrost, floor heat, etc.) Also, it is not dual control. Is the case you are referring to the large black box inside the dash behind the glove box compartment? Thanks.

 

Josh

[GM-Tech]

You have manual a/c. Auto has the digital display. Yes, the case I am talking about is partly behind the glovebox, but it actually takes up most of the area behind the dash from the centerline of the dash over to the right side.