I have a 1975 Coupe with Air. I have an intermittent problem with the fan. Sometimes it works fine in the A/C position but if I move in to the off position and then put it back on I loose everything. If I wait about a half hour it will work again until it is moved. I will also get no defrost or any fan output. I'm assuming it has something to do with the relay.
Although I do have the wiring diagram I was wondering if any one could help me out with the actual location of the relay or a picture. Thanks in Advance.

Ed

 

Ed,

The two main parts are on the A/C heater box. The resistor and the relay. The relay has an orange and purple wire that get continuity when power is applied to the dark blue wire, the black is a constant ground. The resistor is the plug that is on top of the box and has four wires to it. I forget the colors, but if you unbolt the resistor it lifts straight up and will have coiled wire in it that connect to the different terminal. They burn out from heat and that is why the are mounted in the air flow of the fan.

If the coils are all good, reinstall the resistor and test the orange wire at the relay for constant power. If no power that is your problem. If you have power, unplug the relay and jump the purple and orange together with the fan switch in the high position and tkhe key in the run position. If this makes the fan work then test the thinner dark blue wire at the relay for power at each setting on the fan switch, and the black for ground. If you wave power at the blue and ground at the black and the fan works when you jump the orange and purple together then the relay is the problem.

If the fan works when the orange and the purple are jumped and there is no power to the blue at any switch setting when the key is on then the problem is at the switch. I would at this point recheck the resistor before pulling apart the interior.

You can check that the fan works but applying power and ground directly to the fan motor while it is in position.

Hope this helps.

 

Ed,
The resistor is the plug dead center in the picture and the relay is the silver box directly to the right of the resistor on the side of the box. This picture looks a lot like your motor doesn't it?

Tom

 

Thanks Tom, I have replaced both of those parts in redoing the car. Doesn't mean their good. Thanks for the indepth troubleshooting, you surely a great help. I will get back to it in the next couple of days and PM my results.

Thanks Again,
Ed

 

PM sent to Tom