AC and Heat Doors Squeaking

[510man]

I have '99 C1500 Suburban. My AC and heat doors move in the heater box when the system is off. I can hear them moving and they have started to squeak. A couple questions.

1) Why would the doors be moving if the system is turned off?
2) Can I lubricate the doors without taking the unit out of the truck?

Thanks for any suggestions.

 

[swathdiver]

Depends on when you hear them. They could be resetting themselves or something could be amiss. Don't know the answer to your second as we would need to know where the doors are and how to get at them from behind/above/below the dash.

 

[east302]

There is one air door for the temperature. The temperature door actuator is kind of behind the ashtray, remove the glovebox to get a better look. It's buried up there.

The notched silver dial is a position indicator. Watch the dial as you turn the temperature dial from hot to cold. It should rotate smoothly. The noise you hear may be the actuator hunting...it may eventually need replacement if it cannot keep the temperature consistent with what is selected on the control panel.

Does the air temperature adjust correctly? That is, do you get hot air when the dial is on hot?

 

[510man]

[QUOTE="Does the air temperature adjust correctly? That is, do you get hot air when the dial is on hot?"[/QUOTE]

It works correctly in terms of hot and cold air coming out of the correct vents.

I believe you are suggesting I check #3 Temperature Door Motor in the above diagram. Is this also called a Heat Blend Door Actuator (ACDELCO 1573627)? The noise seems to come from the area where #3 is shown in the diagram. Of course, it's easy to be fooled by where a sound is coming from when dealing with a box.

The moving around and squeaking noise stops if the fan is turned on. It seems to search, as you suggest, when everything is off but it works correctly when turned on and seems to hold it's door positions and temperature as set by the knobs. It's that "off" position that is the problem I never had previously.

Thinking through it, I guess the control assembly could be sending data when turned off. It could be on the sending or receiving end based on the diagrams. #3 is likely the least expensive to try, assuming I have enough access to change it.

 

[east302]

Yes, it's #3 in the diagram. I cannot confirm the part number, but it would be called the blend door versus the mode door for the floor-panel-defrost actuator.

The actuator should only be getting voltage when the ignition is in "run", it looks to be independent of blower position.

That it goes away with increasing fan speed may just be the airflow stabilizing the damper and drowning out the actuator noise.

Given its location, this is the actuator that most people hate replacing.

As an aside, most of the time the actuators make an oscillating (or back and forth) ratcheting sound when they are hunting.