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2002 Buick Rendezvous Heat Problem

I have very little heat into the cabin of my Rendezvous and it seems related to the fan. If I have the fan on high, and the temp selector on cold, I have a high volume of air from the vents. As I turn the temp toward hot, the amount of air from the vent decreases, until very little air is coming out. The fan does not decrease, but it sounds like the air is being diverted or blocked somewhere.

Trips in the winter are no fun and I want to fix this myself.


Air temperature is controlled by the “blend door,” which directs incoming air through either the heater core or the AC evaporator, or a combination, depending on the desired temperature.

Something is preventing air from flowing through the heater core. Determining what that something is could be difficult and time consuming, since it would require opening the ductwork of the HVAC system, which is buried behind the dashboard.

I would try to determine, visually, whether or not the blend door is moving correctly before going any further. If you can see the mechanism which operates the blend door, that is.

What would I be looking for - general descriptions and general locations? I can see the blower motor, would tracing that route be advantageous or not tell me anything useful?

The blower motor is a good place to start. If you can remove it you may be able to reach inside the ductwork and feel for an obstruction.

I don’t know exactly where the blend door is. You’d need a service manual to describe the location and operation of each component of the HVAC system. They differ from vehicle to vehicle.

If you could have someone operate the temperature controls while you look around with a flashlight you might be able to locate the mechanism that moves the blend door. It may be operated by cable (or stiff wire), vacuum, or electric motor.