bg3

Hi

The air blend opens on right turns and ac goes hot. Have to shut down engine & restart for ac to resume
Have a 1996 c4 w/ Digital ac unit.
Door moves when temp set warm or cold- just flys open on turns.
Suggestions to fix or how to rig to keep door in place? I live in AZ so no need for heater.

Cliff Harris

Check out the blend door motor, which is mounted on the heater duct inside the car. I believe on your car it drives the blend door directly (earlier years had a link that could come loose).

It's possible that the gear train inside the blend door motor has a problem. The only way to find out is to take it apart and see what's happening inside. There was a post showing the insides of the blend door motor, but I didn't bookmark it so I can't provide a link.

bg3

Well, its always something!

I wonder if I can tack/glue the door to keep it on the AC side. I don't ever need heat or defrost- I live in AZ. Sound reasonable?

pcolt94

I would first determine if it is really loose. If you remove the blower module in the evaporator, you will be able to see the blend door. You may be able to reach it with a stiff piece of wire (coat hanger) and see if it is loose.

If you remove the door motor, you will be able to grab the door shaft and check it out. You will also be able to see if the motor is locked in position as it should be. It's best to remove the 2, 7mm screws with a very short 1/4 " drive ratchet (a wrench will be a pain). The best tool is one of those round flat ratchets.

You can also see the door move if you have someone run the temp from cold to hot (key on, engine off) which is another data point to see what's working or not.

bg3

Well, the door swung freely when on COLD and properly when on HEAT. As I didn't have the time to pull the evaporator apart, I tacked the free swinging door closed to the COLD side with some rubber trim glue, and voila- for the first time since I have owned this beast I get cold air- even when I turn right!

Now if only I could figure out how to get air out of the front vents instead of the defrost and the floor.

Cliff Harris

Look under your fuel rail covers (I think it's on the passenger side) for this guy (vacuum check valve). The one on the left is for LT1s and the one on the right is found on L98s.



It's probably bad. You can get a new one at any auto parts store for less than $5. You might have a problem with the vacuum hoses associated with this valve. It supplies vacuum to the HVAC system and also to the cruise control.

bg3

Thanks. I will replace the vacuum check valve. Tacking the blend door was the right move.

pcolt94

Don’t pull the air box apart yet. A free swinging door is not a common problem. Having stripped gears in the motor blend door would really be out in left field but not impossible. I mean it would take a lot of force or abuse to damage the motor gears but worth checking out. However I am going to go out on a limb and tell you to check to see if even the motor is there. If it is that lose, it sounds like it is almost freewheeling.

Start at square one. Locate the motor and see if it is there. Then inspect the shaft and the motor insert where the shaft goes. Then try to move the motor drive by hand and see if it is lose. If it is, then you can open the motor up and check it out.

Here's the kicker, you will have to remove the lower kick panel on the passenger side to get access to visual see the motor (Kind of above your left foot if you were sitting there). This will take some disassembly of vents, fuse box screws around it and nuts behind the right side air vent. Consider alllll the plastic brittle and don’t pull or force hard on anything. If you can't get it apart or know where to start, ask.