A/C Stuck on Defrost-Vacuum Leak

[JRA2000TL]

Need help with my brother's 95 ATX. He had to work this afternoon, but I'm going to try and help him fix this. He just bought the car and the a/c worked great. The next day the compressor died. $1200 later, he has a new compressor, accumulator, orifice tube, etc. The repair shop was going to go ahead and fix the problem of having the a/c stick on defrost mode (did this when we picked it up). He initially said the EATC was bad and wanted $250 for a used one. We laughed and picked the car up. We have 2 spare hard buttons we tried--no fix.

I did a search on here and found that it's one of those colored vacuum lines that goes from the EATC to somewhere in the dash. I pulled out the shop manual and found the vacuum diagram. Does anyone know which line is usually the culprit? I found where the red and blue lines go to a metal canister thing under the dash near the glovebox. I didn't detect any vacuum when I pulled those loose as the a/c was on.

It's not the BDA, not the BCM (blower shuts off when the EATC is off), has an entire new a/c system otherwise except an evaporator, 4 different EATCs have been checked. It HAS to be a vacuum leak, but we need help locating it.

 

[St Louis SHO]

I think its the mode door motor (vacuum) operated. I've done a bit of research myself and thats the best I can come up with. If you unplug the vacuum to it, and plug it back in it'll work. I think the diaphram has a small tear in it.

- James

PS the best way to test it is with a vacuum pump (hand) pump it to 5/7psi and see if it holds.

 

[JRA2000TL]

Where is this thing located? Do I need to tear the dash apart or can I pull the glovebox out and get to it?

 

[St Louis SHO]

Glovebox, it'll be on the LH side. you'll see the vacuum hoses.

 

[SeanMc]

Mine is doing the same thing. Thanks!

 

[Bill Strobel]

If it is not a vacuum leak then the blend door lever is broke. With the A/C on try moving the selector switch to the right on one of the heat modes. If the air comes out the vents then the vacuum is OK. It could also be mode selection switch itself but this is rare.

 

[SeanMc]

Mine comes out ice cold through the defrost, and very little comes out through the 2 middle vents. James suggested I get a vacuum pump on the mode door motor, and if it's not that, check the hose under the hood between the heater hoses. I don't have any leaks under the hood, but I hear something inside. When I get a chance, I'm going to tear out the EATC, and check the hoses.

 

[JRA2000TL]

Post pics of what you find. We may take a look at his Wed. or Thurs. when he's off work. I told him to bring it by the house. Don't think it's the blend door since pressing defrost, floor, then max a/c gets cold air through the vents. Heat will also blow through the vents once this button sequence is pressed (if the temp is set to something like 85 or 90). What's funny is that sometimes the air will blow out of the vents immediately if the EATC is turned off, then on again.

 

[St Louis SHO]

If it is not a vacuum leak then the blend door lever is broke. With the A/C on try moving the selector switch to the right on one of the heat modes. If the air comes out the vents then the vacuum is OK. It could also be mode selection switch itself but this is rare.

1 out of 5 times, it works correctly (In JRA's case) So, I want to believe the diaphragm has a slight tear in it. It was my dads car, and one day he came out and it didnt work. I'd play with it and it would. Sure acted like a EATC, but we swapped it to no avail.

- James

 

[JRA2000TL]

I wish I had better pictures of this thing. I just have my 90 shop manual which is going to be very similar in regard to the EATC. The vacuum diagram shows the wires, color, and how to diagnose the problem; however, the picture isn't very good in the fact that it shows that whole assembly in a separate picture (but not actually how it looks in the car). I'm one of those that can fix things if I have detailed write-ups with pics, but I'm not good at figuring stuff out. I'll pull the glovebox and trace all those color coded wires to check for vacuum. I've also read about this diaphragm issue in an old post. It was the cause of someone else's problem on their Gen I.

 

[Bill Strobel]

The fact that you can get this to work sometimes means the vacuum is OK. I know earlier this summer I had the same problem. All the troubleshooting trees pointed to a vacuum leak but it was the blend door. This is the blend door the controls the defrost/vents. It is part of the plenum itself not available separately. They usually can be fixed but the dash has to be dropped, not removed just tilted forward. If you spend more time looking for the vacuum leak and do not find it, then try this. Remove the radio and the storage compartment. While moving the control try to get the blend door to move to vents. If it moves look or feel the blend door moving you can the see it is broke. One more thing if you can get the air to come out of the vents do you hear a clunk? If so broken blend door. Hope this helps.

 

[St Louis SHO]

Mode door.

You can hear it shutting. So the door isn't broken, which means go to step one. Diaphragm.

 

[Bill Strobel]

If you hear it shutting with a clunk then it is broken. That's what fooled me. You should barely be able to hear it if it is normal. Pull the radio and storage compartment and watch it, you'll see that it is not right. It is the lever that works the door that is broken.

 

[Cl-Slick]

Well, Jeremy and I are taking a look at it tomorrow since I have the day off. Thanks for all of the advice guys!