Heater

[rimares]

I am having a problem with my heater. In the morning it is cold, so I turn the heater on. Then as it gets too hot I try to reduce or even eliminate it, it doesn't get cold til I turn off the truck and restart it. Any suggestions?

[8.1HD/ALLISON]

I would check operation of the temperature blend door actuator.

[Scottorado]

I had the same problem on my 2001. I removed the actuator and found it was binding up when turned to the full hot postilion. What I found was the actuator servo was not factory calibrated correctly. Inside, there is a position potentiometer (pot) geared off of the output gear. It was off one tooth so that the servo would continue to try and drive the output gear past the stop on the case, causing the gear train to bind up and stick. Removing power let the gears relax and then it would work again.

 

I opened the actuator and carefully moved the blue position pot gear one tooth until the servo ran freely, stopping gently at each stop. It now seems to work fine.

 

I don't believe the heating system is tied to the computer on my 2001 LS at all. It does not have dual climate control. Other years and trim levels will differ.

 

WARNING:

Dissembling the servo (actuator) can result in loosing synchronization of the position pot, and if you are not familiar with servos, you may never get it working again.

 

Also, there is a GM bulletin about actuators that says not to apply power to a loose actuator. (I did a bunch of times with no problem, but consider your self warned, it may vary by year and trim level)

 

Scott

[Scottorado]

Ignore my above post. I still have the hot air sticking on, but only after it has been hot a while.

 

Scott

[mkimber]

I replaced the actuator and its been working fine for 3yrs now. I think the plastic on the blend door swells with max heat for several minutes and the actuator can't rotate the door when it happens. I used to set it about 75% heat and turned it down to 50 or so after 5-10 minutes and it wouldn't get stuck as often. I finally got fed up with it and got a new one after 2 winters. Easy to replace but I think it was about $75.

[Scottorado]

I did some more testing. When it gets hot and stuck, the actuator tries to move the door to cool, but only goes a few degrees and stops. It acts like the door is suck, but as strong as that motor is, I find it hard to believe that is the case. My other idea is the actuator is malfunctioning electronically when hot.

 

If the door is physically sticking, changing the actuator will not help.

 

I have the actuator out, so I will take it for a drive and see if the door is sticking by hand.

 

Thanks,

Scott