Heater Door Question

[Chris Kennedy]

After going through all the relevant threads on the Forum, I finally decided to check to see why the heater door on my '89 wasn't opening (the car has the electronic controls). I think I found the reason, but want to run it by the group. First, all the switching functions work perfectly---all air goes where it should, etc., AC is great, but there is no air warming (if you turn on the heat, the air goes where it should but is not heated). I have a spare door actuator motor, plugged it in, and watched the arm which controls the door move when I turned on the air conditioning. It moved fine, then stopped as it should. When I tried the heat it didn't move the other way. So, this spare motor seems to confirm that power is getting to the motor, but after it moves to the (probably) AC position you cannot get it to move back to the heat position. So, I suspect that there is no problem with the motor that's in the car as it's "stuck" in AC the same as the spare/test motor was after the test. Anyway, I checked the service manual, and what I think is happening is that the main control unit (the part with the function buttons above the console and NOT the programmer), is grounding the the electric motor to move it to AC, but is not grounding the function which reverses polarity and runs the motor the other way so it opens the door to the heat when you press heat. Interestingly, the manual says that that the main control unit grounds the appropriate terminals in the main control unit to run the motor to AC or heat, yet the wiring diagram indicates that these terminals that are grounded are in the Programmer! Is this an error?. If all the grounding circuitry is in the main control unit, then it would appear to be the problem. But, if part of the grounding circuitry is also in the programmer, it could be the problem. My gutt tells me that, regardless, the problem is with the main control unit. What do you guys think?

Thanks,

/s/ Chris Kennedy

 

[jsinga]

I don't know if this has anything to do with your problem. Some of the control unit boards warp and the contacts don't mate properly.
Maybe someone can tell you what the fix is. I think you might even be able to fix it with some well placed ty-wraps.

JS

 

[Chris Kennedy]

Thank you very much for this reply! I will be going through all this on the weekend and will report back.

/s/ Chris Kennedy

I don't know if this has anything to do with your problem. Some of the control unit boards warp and the contacts don't mate properly.
Maybe someone can tell you what the fix is. I think you might even be able to fix it with some well placed ty-wraps.

JS

 

[jmccloud]

Heater control

Different year ('95) and different control (mine is 'manual' not the electronic temp control) but you may have a similar problem.
My compressor ran all the time until the outside temperature dropped enough that the low pressure switch cut out (about 40F ambient). It was caused by a shorted transistor in the 'manual' main control unit (yes- the panel on the dash).
About $1 part from Radio Shack and it now controls as it should. I found the blown (shorted) transistor by checking resistances but should have looked at the parts first; the shorted transistor looked like a peeled banana - easy to spot.
Perhaps this is from left field but the transistor logic in the dash panel unit may be your culprit too.
The service manual (the good Helms books) did not show any electronics inside the main control unit. I had to figure out the logic.
Hope this helps

 

[C-4 Now]

When my 89 did this I ran most of test in service manual and ended up replacing controller above accelerator. I also have C-68 automatic temp control. Good luck. Trouble shooting test is long. :cry

 

[Chris Kennedy]

Thanks, everyone, for your advice. Interestingly, I have the compressor issue, too, that was mentioned above. I have a "test" unit controller on its way to me, and after some detective work I am pretty confident that the programmer is o.k., but have a test unit for that as well. I will try the controller first, and see what gives. If not, then the programmer. Regardless, I will report back.

/s/ Chris Kennedy
Houston, Texas