Hi,

I have a 96 Regal Custom with manual dual zone climate controls. When dual option is turned off and temp lever set to cold air, I get hot air from the bottom (floor) vent on the passenger side. Other vents blow cold air. Yesterday I have also noticed that even I got the heat on while I was driving, vents started to blow cold air (it was approx 32 deg outside :frown: ). When I shut down the engine and turned it back on, the problem was gone. I have also experienced problem with vents switching from front to floor when the AC is on. But that was only in summer time when I used AC. Heat was OK up to few days ago.

What could it be? My friend said that I should check the thermostat but I think it is something with vents (motor). Anything I could check myself or should I just get it checked out by professional mechanic?

Thanks.

Which engine do you have? 3.1L or 3.8L?

The HVAC system uses electrical and vacuum controlled actuators controlled by the dual climate control unit. So it could be an actuator. Also, make sure the accessory vacuum supply to the HVAC is good or not missing. Inspect the vacuum lines. The vacuum source originates at the area of the intake manifold.

Is the engine operating temperature normal and the temp gauge reading correctly?

I have the 3.8L engine. All gauges are working correctly. At least I have not seen any abnormalities in the temperature reading from what I remember when the system was working correctly.

Where can I find the actuator? Is it easy accessible and can a noob like me tell if it is not working by just looking at it?

Thanks.

Since the temp appears to be OK I would rule out the thermostat for now.

The dual climate should have two temperature actuators (driver and passenger side) located to each side of the lower part of the HVAC assembly in the dashboard. Also, there are vacuum operated actuators that control the various modes and vent/air direction. The lower dash kick panels will need to be removed to perform an inspection or do further troubleshooting. Also, if you remove the glovebox door you may be able to better access the passenger side temp actutator and some of the vacuum/electro actuators. A GM service manual or similar may be helpful to correct this type of problem.

BTW - The accessory vacuum line on a SII 3800 is on the backside of the UIM plenum (plastic upper intake). There should be a Y vacuum connector where accessory vacuum will branch off to the HVAC system.

Thanks bnaylor. I will get to it this weekend. Hopefully I can diagnose where the problem is.