|Hey, I got a 89 cabby and when I use any air settings including A/C the front defroster blows out hot air, the defroster turns on at the same time and runs at the same air settings. The switch is fine being that I can put the a/c at 1,2,3, or 4 an cold air comes out of the vents, but the defroster seems to like those settings also because it spits out hot air on the same air speed settings. It’s unbearable to drive even with the top down; it heats up so much the dash gets to be so hot u can’t touch it. I also had took out my cd player cause it started to heat that up so bad I could smell burning. I don’t know what the deal is with it. Someone said the wires from the a/c and heater could be crossed when they get to the blower but I’m not sure.. HELP PLEASE!! Being like this in the summer SUCKS!
If your defroster is continuously spitting out hot, then I would suspect that the cable that controls the heater valve on the firewall is broken, or severely maladjusted. You can check this by moving the selector to full hot, then go out under the hood and look for the two heater hoses that are in the middle of the firewall. On one of them usually closest to you there is a plastic valve. Look to see if it is against the stop. Now move the slide selector all the way cold it should move the valve against the other stop, if it isn't then the cable is broke. It really isn't a cable but a steel wire inside of a shield. To turn the valve off, just move it to the stop.
You didn't say if your defroster is on all the time or is the only thing that is working. Ie: can’t go from defrost to front vents.
It does continuously spit out hot air, even if the speed selector that controls the air on all settings is off. No air comes out of the defroster but in about 10 min. the whole dash is hot, so something’s heating up back there... the a/c is fine though; cold air comes out of the vents -- except the center 2 vents (the valve in the back of the center vents is stuck shut).
I know that the valve back their diverts cold air from the defroster to the center vents; mine is stuck shut so that explains why air is coming out of the defroster ports all the time but it doesn’t explain why its hot air all the time even if the a/c's on. Any ideas on how to fix that valve in the back would be helpful 2.
Better advice than I could have come up with - find one and compare it to yours...
If one vent (defroster) is open, the other (center cold air) is usually closed, just like you describe. The "default," I believe, is the defroster setting. Some people have just disconnected their levers and closed off one or the other manually according to season.
It does also sound like the heater valve is stuck open. It is accessible in the engine bay. Check the cable before you try to replace it - it may be stuck on something.
Sounds like you have two problems, one is the vacuum servo is stuck that puts the heater air in the heater box. The second thing is that the heater control valve is always on. I suspect that the cable may be off the arm on the valve, and your valve is in the on position.