AC heater fan switch repair
 

I’m in the process of replacing my factory engine in my 75 TA. I paid a fellow to help me with some things. We installed a new heater core and found the burned up fan switch and connector.
Unfortunately the guy bailed on me. Oh well.

I found some pics of how the air conditioning and heater switches work. I’m eliminating the AC but keeping the heater. In the comments with the AC and heater wiring the fellow wrote that this was common for those to burn up. My question is what is shorting out to cause that?

I also installed a smaller box to get rid of the AC condenser box.

I’m aware of the weird grounding for the fan. I need to double check that the guy helping me grounded directly from the fan motor as it says in the directions for the heater firewall box.

Thanks for any help you can give me!

Nothing is shorting to cause the AC switch to fail. GM failed to provide adequate contact size and or the correct material inside the switches. So when you turn the fan on the the load of starting the blower motor causes the contacts to arc. Over time the arcing destroys the contacts and either the switch quits working or the contacts get hot and overheat the switch and wiring. Which then let's the smoke out. 😒

You can rewire the switch to operate relays which in turn will operate the blower motor to correct the problem.

Thanks for the reply ! That’s a big help.

You're welcome.
Good luck with the switch.