HVAC 5 volts

[Timd]

I am troubleshooting my heater that wasn't working, I removed the blower and connected it to the battery and it works perfect so I tested the wires behind the dash and they are producing 5 volts with the key on but not running, does anyone know if this goes up when running or is there something else wrong?

Thanks

[Busboy]

It depends on which wire your checking. Get the wiring diagram out. There should be less voltage on low and/or medium speeds than on high.

[1972hiboy]

If the blower motor runs on full 12v its most likely not your culprit. Your going to want to focus in on the blower switch on your heater control panel and blower motor resistor. I've seen a lot of the time if the resistor goes bad it will usually default to only having its highest speed and none of the lower speeds will work. If your just not getting anything on any speed start at the fuse block. Then check to make sure your getting power to the blower control switch, then onto the blower resistor.

[Timd]

If the blower motor runs on full 12v its most likely not your culprit. Your going to want to focus in on the blower switch on your heater control panel and blower motor resistor. I've seen a lot of the time if the resistor goes bad it will usually default to only having its highest speed and none of the lower speeds will work. If your just not getting anything on any speed start at the fuse block. Then check to make sure your getting power to the blower control switch, then onto the blower resistor.

Thank you

[Timd]

Where would I find the resistor or can you point me to the wiring diagram? I cant seem to find it.

Thanks

[1972hiboy]

The blower motor resistor is going to be mounted to the heater box near the blower. If I can recall it should be on the inside of the cab mounted on the heater box. Its going to have a substantial plug going to it with several wires in the plug. On a truck with only heater equipped it should be the only thing with wires going to it besides the blower itself. sorry that may not be too helpful. I don't know if i have a pic or not ill check.

[Timd]

Awesome thanks. With my tester hooked up it doesn't matter what setting the heater switch is on it still only reads a little over 5 volts. I will check the resistor tonight.

[1972hiboy]

Awesome thanks. With my tester hooked up it doesn't matter what setting the heater switch is on it still only reads a little over 5 volts. I will check the resistor tonight.

The switch may only be sending a signal voltage to blower relays that supply the battery power to the resistor, In which case most of the dash operates on around 5 volts so that could be correct.

[69Ford]

If this helps here's a picture with the heater box removed. This is the firewall side. You maybe able to get to it out with patience "just two screws or ratchet head screws". Without taking the heater box out.

Back Side3.JPG

[1972hiboy]

This is what the blower resistor is going to look like. the coils will be on the inside of the heater box. Nice picture of the heater box 69 ford that's perfect!

[Timd]

Awesome, thanks guys.