alright guys i have a 99 gmc jimmy envoy. i cannot get the mode selector for vent, defrost, floor etc to work. wherever i click it to it still comes out of the dash. the blend door actuator is good. that functions properly. is there a mode door actuator? if so where is it located? could the mode selector switch be bad? im stumped. please help. thank you in advance guys!

 

There are several vacuum actuators in the dash. Some have one vacuum line, others have two. The Black line at the mode switch must have vacuum while the engine is running.

 

Thank you for the response. Actuator wise I mean the one that bolts in not the ones that have the plunger. How many actuators are under the dash that bolt in?

 

The blend door actuator bolts to the top of the heater case with 3 screws, and it is electro-mechanical, (no vacuum). It regulates outlet temperature only. There are, (I think) 4 vacuum actuators that control where the air flow comes out.

 

Alright captain hook. So there is only one electro mechanical actuator? The rest are the plunger type that the vacuum lines hook to?

 

Assuming you have manual HVAC, there is only one electro actuator. If you have automatic climate control, there could be up to 3 of them.

 

Where does the vacuum source come from for the mode switch to operare from?

 

The black rubber vacuum line from the engine connects to a vacuum tee under the hood near the power brake booster. From the tee, it runs forward along the left inner fender where it changes to black plastic and enters a wire harness with black plastic split loom around it. From there it goes through the firewall into the cabin, and then to the HVAC mode switch.

 

Alright an update....I found the black line under the dash unplugged it to make sure there is vacuum there and there was. So i went to the junkyard and got a blower mode switch out of a 97 s10, hoping they were the same. They are vacuum line wise but the rod that goes thru the mode select curcuit board is too short. So I kept it out of the board for now and turned the switch to different settings. It finally sounded like it was switching thru the different selections but it would not switch to defrost or floor, it was still stuck on dash. Any clues?

 

Disconnect the vacuum connector from the switch. Does the black vacuum line in the connector hold vacuum for at least 5 minutes after you turn the engine off? (stick your finger on it to seal it)