2004 GMC Yukon – No Heat

DDaley: I have a 2004 GMC Yukon SLT with 5.3L V8. I’m having an HVAC problem. The vehicle has dual climate controls. When in AC mode occasionally it will start blasting out hot air and the only way to fix is to shut off engine for a little while and it resolves. Ok, so now that winter is here and I need heat it starts up and blasts cold and sometimes kicks over to heat and sometimes not. I kinda wonder if the blend door actuator needs recalibrated??? If so can you instruct me on where to get that procedure. If its not that system can you advise on what to do?

Sparky: You can try a recalibration but more than likely you have a problem with the actuator itself. I am assuming that the driver’s side is acting up and the passenger side is okay?

Here is a link to an article I did on actuator recalibration.

DDaley: No, neither side was blowing any heat. I checked the coolant level in the vehicle and it was low so I added coolant up to normal and heat then started working so it probably was to low to get into the heater core, so that helped. BUT NOW the fan can be running at high speed and heated air either does’nt come out any of the opening or it comes out randomly (not where its set for).
It sometimes comes out defrost only or panel only or floor only or sometimes not at all even with fan running and temp set for heat. The heated air from blower just doesn’t seem to come out the selected opening???? Any ideas???

Sparky: I recently had this same conversation with another reader. They had to top off the coolant system several times (with driving cycles in between fills). That too may clear up your lack of heat problem. Installing a new mode actuator will likely cure the vent control problem. Did you try a recalibration of the system?

DDaley: I did recalibrate the system as per your article. Thank you. What is a mode actuator? I believe you are talking about the blend door actuator. Is that correct? If so is there just one on the passenger side or are there two (driver and passenger side)?

Sparky: There are a total of four in the front HVAC system.

Mode actuator is located on the left end of the HVAC case assembly just above the gas pedal area. It is responsible for where the air comes out of the dash.

The Driver’s temperature door actuator is located under the passenger side of the dash above the transmission hump in the floor pan.

The Passenger side temperature door actuator is located on the passenger side of the vehicle on top of the HVAC case assembly. Generally to the right of the radio and about a foot back.

The air inlet actuator is located behind and above the glove box area.

DDaley: OK cool, so you believe I need to replace the 1st one (mode actuator) on the above list to resolve the random air movement I described. Correct? If so, do you have a link or something that describes that process. Thanks for your help.

Sparky: Here is link on replacement instructions. 

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