pcolt94

Another long one. These are the highlights, I have left out the dull and dragging on details. I was way beyond asking for help on the Forum. Another great learning experience.

This has been an on and off problem for a year or so where I could not get heat or just loose control of the mix door motor. Early on, every time I removed and reconnected the motor connector it would work for some period of time, however it felt damp down there at times.

When it crapped out again I removed the motor and found it was loaded with water. I took the case apart, cleaned and dried it out, tested it with external power. Put it back on the car thinking I was fixed. I figured the evaporator case has a partial clogged drain and cleaned it out. Since then no water problem.




The motor and the rust - this did not happen overnight


Once again it crapped out. Pulled the motor again, ran the motor with external power, checked the variable pot and lubed the gears. But this time I was not sure of the gear alignment and thought I had it right. Installed it and it worked. Two weeks later disconnected battery for another reason and the motor problem surfaced again. But this time symptoms are different for the motor always wants to drive continuously cold, or sit there and oscillate when driven to hot. I was getting an error code 01 (temperature door motor circuit).

Fast forward. Now I have the programmer out and troubleshooting more of the system. Took the main circuit board out of the box, left the box in car due to vacuum hoses. Feedback (pot) voltage was there on the card. Ended up checking the capacitance of the filters on the circuit card as well as other items. I could see the drive voltages going nuts and figured the big chip was bad.



Circuit card, component side (94-95)


So I went the used vette car place to buy a programmer. We tried 2 in there and did not fix the problem to my amazement. He says come back next week and you can try a control head. So with my tail between my legs I left. But I really did not think it was a control head problem.

Got home, pulled the center section apart and got out the controller. Now I’m ready to try another one. Figured since it was now hanging out I mind as well take that apart and look at it. So I cleaned all the internal connectors and buttons, solder still looked good from last time I did it. Reinstalled it, no change but my flashing OFF LED problem is now fixed.

Now I spend the next few hours checking the car wiring from motor to programmer and more. At one point I thought I had something but ended up finding nothing, all was good. I starting thinking about the motor again and that there was something I had missed. It all worked till I powered down the car, puzzling.



Card out of box so I could make measurements. Surface technology resistors and capacitors.


Once again I start looking the FSM hoping there was some tid bit of information I could use. I came across a test step that asked you to measure the resistance of the feedback pot in the motor at the cold and hot position. I had done this but as I thought it was OK. But since I could not control the motor now, how could you do it. I pulled the motor off again (as if it has not been on and off 50 times) and used external power and drove the motor to the place I thought it should have been for full cold. Then installed it to make sure it was a mechanical fit for mix door to be full cold also. When I was happy with the position I measured the pot (motor pins 8 & 9).

According to the FSM it should measure 1.95K +/- 500 ohms. It measured about 300 or 400 ohms. So took the motor case apart again and re-aligned the gears so the pot would measure as close to the target resistance as I could get. I think I winded up with 2100 ohms. Your restricted to one tooth alignment plus the gear slop. I figured even a miss-alignment it would just servo to the wrong place, apparently not.

I installed it back in and I could not believe it worked. I must have miss-aligned it (or not?) when I had it apart at one time and not realized it. So now it is all working and obviously the controller and programmer are all good. I am driving for a week before I put it all back together.

Hers the kicker. I have made a full circle and fixed what was “miss-aligned”. But what have I really accomplished or fixed from the original problem. Maybe the water was a factor, I just don’t know for sure. Will something act up at a later time, I hope not.

Once again got my brains beat out but that’s one more system I know well.

Anybody else been down my road?