THe Switcher for the heater/AC wont work?


Asked by Nov 30, 2014 at 05:05 PM about the 2000 Chevrolet Blazer Trailblazer 4-Door 4WD

Question type: Maintenance & Repair

The switcher thingy (don't know what its called, modulator or something like that) wont work. When we switch from front cabin panel vent heat to windshield heat it doesn't change and still blows from the front vents into the cabin. (its a year 2000 blazer I think) and my grandpa wants to get it fixed. I own a 05 Chevy Venture and I can hear a switcher make the air change from blowing from the front panels, to blow out of under the windshield or vents to the feet, I don't hear such a change in my grandpa's blazer so I think the switcher or whatever doesn't work, we cant even get the feet vents to work. Any ideas on how to fix this or? the switcher we use to change modes does work but its whatever inside wont make the air redirect to windshield or Feet vent.

4 Answers


Most cars use a vacuum directional switch and actuator to change air flow positions. They do wear out. Sometimes the seals in the position switch get blocked and fails to send vacuum to the valve. There is a resistor in the unit that may have went bad .... not that hard to change ...You can find it here

1 of 1 people found this helpful.

It's called a HVAC door actuator. The main one (called the blend door actuator) is in the HVAC box along with the AC & heater coil - that switches from hot to cold. There are other ones - depending on make and model - that switch air direction from floor to dash vents, recirc, etc. You'll have to figure out just which one is not working, order the part (they're cheap), then replace it. Usually you'll have to go through the dash to get to them, the ones for the vents are easier to get to, you can often go through the glove box or air bag opening. I see a ton of youtube videos on how to replace those actuators. Before you go ripping into your dash however wouldn't hurt to check you got power to and from the HVAC controls.

3 of 3 people found this helpful.

I was able to get to the actuator from under the dash ... I needed another joint on my arm to change it ,,, only to discover it was the rotary switch ... Duh

1 of 1 people found this helpful.

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