87 D21 Heat/Air control wiring.
87 D21 Heat/Air control wiring.
I recently inherited my step father's D21 truck. My step father did most of the upkeep and repair on the truck. Some he should have left to professionals. I have found modifications to the original wiring on the truck. The area that I'm working on now is the heater. The symptoms are: In the off position the blower works at a medium speed. In the low, medium, and highest speeds the blower works at a medium speed. The 3rd position (medium high) the blower works at a higher rate than the other positions. I have removed and checked resistor. All the coils are in place and appear to be working as they should. Continuity and variations in the resistance. One item of note about the resistor, the shorter of the three coils heats to a glowing red. I have removed and cleaned the switch from the inside. Didn't find any broken bits in the switch. Only thing that appeared irregular about the switch was a short jumper wire to the large black wire in the switch group. The conclusion I have come to is the wires to the switch have been moved around or the connector in the resistor plug have been moved around. I have found the wiring schematics for three connectors to the resistor cluster but not the five connectors in a double row six position plug. Any photos or detailed by color wiring diagrams would be greatly appreciated. Thanks for your help, Robert.
Re: 87 D21 Heat/Air control wiring.
I have disassembled the plug to the resistor and have tried several combinations. I think I have gotten it mostly correct. I haven't been able to wire it so the blower is completely stopped in the off position. Do this model normally operate with the blower working in the off position. I remembered GM wired their blowers to operate on low to maintain a level of ventilation. Is the the situation with this model?