HVAC stuck- wont change modes [Archive] - GrandAmGT.com Forum


View Full Version : HVAC stuck- wont change modes

09-22-2006, 10:34 AM
Well this morning I was on my way to school and I turned the defog/lower mode on and it worked. After a while, I noticed it was getting a little chilly in the car. I switched it back to bi-level and no heat came out. The fan motor sounds like its working at all speeds, and I can hear air moving but dont feel the air coming out from anywhere. Any ideas what this could be? I did a search and it suggested a vaccum leak, but my car seems to be running the same...a vacuum leak would affect performance and idle.

12-19-2006, 09:30 AM
what did you find out about your vaccum leak. i think i might have the same problem. last time this part of the car was a problem i needed to replace that regulator or what ever they call it on the firewall. this time different at times never no when or for how long i just do not get any air/heat coming threw the vents.

did it the other day . i drove to the rink no problems , come back out after hockey game , no heat . turned the dial that positions it from you know feet to defrost etc , back and fourth few times then set it on off for a mintutes or so . then all of a sudden everything was okay heat back. wife just called me today to tell me it off again. i

f it is a vaccum leak where do you look in particular , under dash , behind dash ( would be a bitch ) , or under the hood etc etc

12-19-2006, 05:09 PM
A vacuum leak would mean the vacuum lines under the hood running from your engine to the various components of the car. I have not since had this problem occur again, so i'm not worried. Don't know what it was, so I cant help you. Sorry.

12-20-2006, 04:19 PM
the control head supplies vacuum to the mode door actuator recirc door vent door and defroster door. when you turn it to max, the vacuum hose routes to a vacuum actuator that operates a door over the blower motor and only uses inside air. when you turn it to anything else, it changes the door position. a good way to see this is to take the glove box out, the recirc door is right there. there is also another vacuum actuator that changes the modes, but ill get back to that in a min. what u might want to check is the air temp actuator. when you have the glove box out, look to the right side. you will see a little electrical motor that looks kinda like a half elipse with a siver actuator sleeve on it. that is the air temp actuator. with your car on, turn the temp from hot to cold. if this moves(watch the silver actuator turn) then that part is good. sometimes you can hear the worm gear motor run

ok so if thats good then you might have to look at vacuum to the defrost door and actuator. it is mechanically linked to the heater door. so when one opens, one closes and when one is partially open, the other is also. and the vent is a separate actuator and door. all of these doors are located under the dash on the right and left side of the center console. just watch the plungers on the actuator when you change modes(with the car running of course, otherwise, no vacuum.) and make sure they move. also you can use a hand pump and apply and bleed vacuum to watch them work also. if those are ok, then i would check the integrity of the hoses. start with the connection to the hvac control head, they may be loose. youll know which ones they are, there are 2 supply lines that run in to the control. behind the mode switch there are a few vacuum hoses, you can trace down the positions of the switch and look at the corresponding hoses to route down which ones go where. make sure they are connected right and that there arent any leaks or trash around them. if all those hoses and actuator work, then it is prob the control head itself. the only good way to be sure is to replace with NGP(known good part).

also make sure it isnt ur blower motor or resistor by changing the fan speed and listening for the fan to go up and down in rpm