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Blend Door replacement on 1998 Chevrolet Blazer

12-11-2010, 10:34 AM
I need pics and step-by-step instructions on replacing a blend door on a 1998 Chevrolet Blazer. I am getting heat at bilevel and defrost but not the floor. Please help!

12-11-2010, 04:15 PM
i have the same prob, just been to lazy to do anything about it. pretty sure the dash has to come out... the heater core how to should have some good pics.

12-11-2010, 08:16 PM
This applies to the manual HVAC system only, not automatic temperature control.

It could be the mode valve actuator, (top left side of heater case) or more likely the heat/defrost valve actuator, (bottom left side of heater case). Both actuators have two vaccum lines attached to them. It could also be a binding blend door, or a problem with vacuum distribution to the actuators. You can troubleshoot and replace both actuators without removing the dash. If a blend door is binding, (and the actuator is not causing the binding), the heater case will need to be removed and split apart to repair it. The entire dash must be completely removed from the vehicle to gain access to the heater case, (might be a good time to replace the heater core).

With the engine at idle, temperature set to FULL HEAT and the blower set on HIGH:

At the mode valve actuator, the yellow line should only have vacuum in the OFF and HEAT positions. The brown vacuum line should only have vacuum in the following positions: MAX, NORM, VENT, & DEF.

At the heat/defrost valve actuator, the blue line should only have vacuum in the following positions: MAX, NORM, BILEVEL & VENT. The red line should never have vacuum, it is vented to atmosphere at all times.

You should be able to see/feel the blend doors move when vacuum is applied or removed.

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