Climate control, all defrost all the time.

[GTOger]

I've been through the service manual and cannot seem to find the right way to diagnose this. Wonder if I could get some guru help.

The climate control box lights up, appears to function fine. Temp set will adjust temp up and down, fan speed works, can press the recirc and various air position buttons and the green lights come on. However, no matter what, all the air is directed out of the defrost.

So I'm thinking the electronics are good, maybe something mechanical? Hoping for pointers in the right direction before I cry uncle and pay someone. Ugh.

Summertime in Texas, one needs all the cold air through the dash vents one can get!

[QB93Z]

I recently solved a similar problem (plus others) on my 1994 ZR-1. My problem with the air flow always through the defroster was due to a pinched vacuum line that supplies vacuum to the AC Programmer.


http://www.zr1.net/forum/showthread.php?t=27542


I have never worked on the HVAC on a 1990, so I don't know for sure where the vacuum line runs. The Field Service Manual is vague/wrong about the source of vacuum. On the 1994, the vacuum source is the vacuum connector on the passenger side of the Plenum. The line runs into a wiring bundle and goes through the fire wall to the area under the dash.


The flapper that directs the air flow to the window shield or the dash AC Vent is controlled by the AC Programmer which is located above the gas pedal. If you can get to the AC Programmer, you can use a vacuum tester to test the operation of the Defrost damper and start narrowing down the problem. The Defrost damper can be viewed by removing the defroster grill trim (be careful with the light sensor). With the grill off, you can see the damper by looking through the windshield.


The "off" position of the Defrost Damper is Defrost so you need the vacuum source, the Programmer, and the HVAC controller to all be operational to get AC out the dash vents.


Jim

[secondchance]

Default position, as Jim stated, is defrost. Once with the motor off and ignition on, I was getting air only in defroster mode regardless of HVAC control button position. I thought it was broken until I realized there was no vacuum since the motor was not running resulting in flapper in default position.
I would start with vacuum to the controller.

[QB93Z]

Good point Yun. Since I found it very hard to get access to the AC Programmer under the Driver's side of the Dash, I suggest starting trouble shooting by tracking down the vacuum source to the AC Programmer. It is black semi-rigid tubing that is about the size of 14-gauge wiring so it is sometime difficult to see in a wire bundle. Remove the Driver side hush panel (lower part of dash just above the driver's shins) and locate the AC Programmer and then trace the vacuum source tubing to its first connector, somewhere under the dash. On the 1994 the connector is on the passenger side under the dash. Then apply a vacuum tester and see if the AC vents work properly.


Jim

[GTOger]

Vacuum! Ah! I wondered about that and lifted the hood and aimlessly poked around some lines... thank you very much for the pointers! I will check it out and reply back with results. Or further questions. Could go either way.

[GTOger]

I've been all over and cannot for the life of me find where that vacuum line connects at the plenum. I *THINK* I found it under hush-panel, tied with a bundle of wires. I can only just see a small part of it, and if I tug on it or push, I can get a bit of play.

Would there be logic to pulling the stereo? (It's aftermarket... in case there's something pinched behind it.)

How much disassembly of the interior should I be doing?

[rush91]

Sir, I'm jealous of your '92 Hawk...... talk about rare! What are your options? Competiton package, aluminum block?

[QB93Z]

On my 1994, the vacuum source for the HVAC controls is the connection on the passenger side of the plenum between the runners to cylinder 4 and cylinder 6. The tubing goes into the injector wiring harness and crosses the rear of the motor toward the battery. I never figured out where it passes through the fire wall. On the 1994, I found the tubing on the passenger side under the dash but it didn't seem right to be there since the AC Programmer is on the driver's side.


Were you able to locate the AC Programmer? It is a black plastic box about 4" by 6" by 1" with a small circular manifold of tubing connections on one corner. It is located on the inside of the firewall above the gas pedal.


It may help to remove the radio. In my case the tubing crossed behind that area of the dash. In my case, I removed the entire upper dash pad trying to get to the defrost damper to test it. I never was able to test the damper due to the restricted access under the windshield.


My suggestion is to get to the AC Programmer and locate the black tubing in the manifold. Then try to trace the tubing from the programmer.


Some C-4 owners have reported a failed AC Programmer. It was not in my case. If you can get the programmer out of its bracket, then you can test each of the dampers with a vacuum source. This would give you a start to locate your problem. I had a spare AC Programmer when I was working on my problem. I sold it to an owner in Norway when I resolved my issues.


Jim