Automatic Heat 77 930

[speednme1]

My automatic heat stopped working. So I decided to take it apart and test the unit and it’s parts. First I checked I had power to the unit by testing the three prong plug. I had power so I knew the issue wasn’t with the car. Then I removed the guts from the case. The potentiometer/knob was seized due to some crud and surface rust on the turning rod. I decided to spray aerokroil to lubricate the rod plus I cleaned out the area really well. After moving the rod several time it was all moving as it should. Then I moved on to testing continuity on the wires, all was working well. I decided to bench test but the unit was still not working correctly. I moved on to testing the micro switches. They seemed to be working too. I then decided to pull out the circuit board and have a look. I tested the resistors, transistors and diodes. With my limited knowledge I determined the issue was the circuit board. A new one is $600-800. So I took my board to my electronic repair guy. After 30 minutes he determined I had a bad transistor. $20.00 later and I’m on my way home. I put everything back together and installed it back in the car and all is working as it should. Here are some pics of my unit. The car is a 77 930...the circuit board had a print date of 1976..so it’s the original board.