A/C Heater Blower Problems

[Bennydog]

Hello I have a 75 C10 with heater and air conditioning. RPO C60.. My heater was not blowing so i decided to fix it. got new relay, resistor, blower motor, and switch inside. It runs when key is on in low like it should. It works in low medium 1, and medium 2. But blows fuse in High. I have checked all grounds and jumped ground to fan and it works fine. I noticed this 2 connector under the relay, and sure enough when i unplug it it does not pop the fuse and just goes back to low speed when high is selected. When i put a light on the connector the orange wire gets power only when high speed is selected. so i unbolted it and it has one wire running through the heater core.. WHAT the hell is this thing... Please help!

[Dead Parrot]

That is the anti-freeze up thermostat for the AC side. It should NOT be in series with the blower motor relay. It should be in series with the high pressure cutoff switch on the other side of the dryer in your picture.

Just looked at my 75 with AC. The connector with the orange and black wire should go on to your relay where the connectors with the green wires are in your pic. The connector with the green wires goes to the AC thermostat.

[Bennydog]

Thank you Sir, That was it. Never trust a previous owners wiring.. Thank you SO much. Everything works tops now!