Heat and A/C not blowing correct temperatures or locations

SAATWOOD

MEMBER
2007 PONTIAC GRAND PRIX
3.8L
V6
2WD
AUTOMATIC
170,000 MILES

When the weather was hot this past summer and I would turn the A/C on, sometimes nothing would come out of the vents, no A/C, no vent, nothing. Then, all of a sudden, the A/C would come on, but it would be out of the floor vents not the middle ones. I would hear a single "popping" sound in the dash and then the A/C would come out the middle vents like it was supposed to. Now as soon as the weather is cold, I'm having heat issues. When I first cranked the car this morning, the heat blew hot air, but immediately started blowing cool air, not cold like the A/C, just cool. I heard the thumping sound yesterday again when I cranked it. I had to get the heater core and water pump replaced about 6 months ago. I've been told about the blend doors. Is there a separate blend door for the temperature and a separate one for the location the air blows? Or could this be some other problem?

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

Short answer is yes. There is a door called the blend door, mode door, and recirculation door.

The mode door determines where the air comes out so if it is not blowing from the proper door all the time then this would be the likely cause.

https://www.2carpros.com/articles/low-or-no-air-flow-from-vents

However, I suspect we have an issue with the control module. The fact that it is intermittent points more to a control issue and the door actuators are just doing what they are told.

What I would do is check the voltage at the actuator when you have the door commanded to a certain position. Then change the position and make sure the voltage on that door changes.

https://www.2carpros.com/articles/how-to-check-wiring

If it does then the door should move. If not, then the actuator is the issue.

If the voltage doesn't change then the module is the issue.

Please run through this and let us know what you find. Thanks

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