My 99 Blazer blend door is on full hot all the time. I have charged the ac and replaced the ac cycle switch. The compressor cycles on and off about 5 secs. I can get thru the small access panel under the hood and push the door to the bypass heater core side when not running but as soon as I start it the door goes back to hot. I recently replaced the heater core also. Someone please help. Blows constant hot air even when off. Has computer controled auto controls.

 

Could be a faulty interior temperature sensor telling the ECC module that the temperature in the cabin is colder than the preset value.

 

I would have to say the blend door actuator may have taken a crap. In the 99s you have an access to this from inside the engine compartment ? I have a 96, just replaced the heater core a month a go and the only way I saw getting to my blend door was from the inside of the car. If you break off the one screw on it the thing can be replaced without taking the entire dash out like I had to do for the heater core. Good luck Amigo.

Oh, when all is ok with everything else, the only time the compressor cycles on and off like you say is when you have it in the defrost mode. You can also try your selector control ( vacum control switch) and see if it is switching properly between heat and cold. Mine crapped out and I think it was about 25 bucks from Rock Auto to replace. All was well after that. I would check that switch first, again, good luck.

 

Where do I find the temperature switch inside?

When i switch from hot to cold with the selector switch the round thing behind the glove box with metal arm does move. Also behind the glove box is the fresh air/recirc door which also works. Both are vacuum controled.

 

The interior temperature sensor is located in the headliner near your head when you are in the driver seat.

 

If you break off the one screw on it the thing can be replaced without taking the entire dash out like I had to do for the heater core. What screw do you break off?

 

before you dive in too deep, you may want to check for loose of broken vacuum lines in the engine bay.

 

i have the same thing with my 00 blazer, i replaced the motor that moves the blend door with one i got from a junk yard and now it doesnt heat or cool. before i changed the motor the ac would cycle on and off for a second or two then heat. but now it wont cycle at all. i should have know the junk yard part wouldnt work as it was unpluged before i pulled it off the other blazer.

 

Greetings from another 2 "r" Garry
I had to have my blend door actuator replaced a couple months ago. Part of the process was to program/calibrate the actuator to the computer (probably the Body Control Module?). I have the automatic climate control, so I'm guessing this reply would only apply to Blazers with the climate control.

 

thanks garry 2000 blazer. i have the same climate control as you. your blazer isnt dark blues is it ? that would be funny two guy named garry with dark blue 2000 blazers. your name wouldnt be short for garrison would it ? as mine is.