Have a Car Question? Ask a Mechanic Online.
You'll have to give me specifics on the make, model year and engine size before i can see if there is a schematic available for that but as a rule, the way they are wired is there is a front blower switch for the rear that can either control the rear or forward control back to the rear switch. There is usually a blower resister in the rear unit that reduces the current to change the blower speeds on signal from the switch.
As I stated earlier, there is one main compressor for the system and the rear unit is simply a second evaporator and expansion valve running off the main unit. The only thing separate are the blower and heater controls within that unit. The refrigerant is running through it at all times when the main unit is running. The blower is the only thing you can shut off.
OK, here's a schematic for you. As you can see, the 2 relays are powered by 2 different fuses. The blower motor switch triggers the relays by supplying trigger ground which then sends the power through the resister and then on to the blower motor. I would suspect your problem is one of the fuses blown out. There is a main 30A fuse in the underhood center. The other is a 10A fuse in the inside box. This info should be able to solve the problem for you. I would appreciate you clicking on the accept button and leaving some positive feedback for me.
Thank you, XXXXX XXXXX was able to help you.