Heater fan wiring question

[70LongbedC20]

Hello,

I've got a little problem with my heater fan. It works, on all speeds except HI speed (which of course is the most important) I put another fan speed switch in, but that didn't help the situation. I suspect I have something wrong with my wiring, or another electrical component. I was hoping someone here had the same experience and solved the problem.

Thanks,

[GMC Jim]

There is a relay that controls the high speed. Relay is mounted to the firewall inside the cab, drivers side , near right side of glove compartment. Check for a bad ground at the relay; also check each wire where it attaches to relay terminals.... clean up any corrosion, especially the ground connections, including the relay mounting to the fire wall. You should hear hear a click at the relay when the panel control is switched to high speed.
Does this truck have air conditioning?; if so, then the curent draw is about 16.5 amps on high speed The heater only standard blower is a 6.25 amp unit.

[CrashEd]

Heres a thread from the FAQ about it.

http://67-72chevytrucks.com/vboard/s...d.php?t=216549

[70LongbedC20]

Thanks for the guiding light!

[GMC Jim]

Note that the FAQ deals primarily with the resistor pack that is located inside the cab air distribution box as shown. This resistor pack controls the fan low speeds The high speed is controlled by the relay (with the dash fan speed switch in 'high' position)

[70LongbedC20]

So what you are telling me, is that either the relay, or the relay wiring is bad for the high speed fan settings?

[GMC Jim]

yes... the relay or the relay wiring is causing your blower not to operate on high speed. you might want to check the blower high speed operation..... just connect a 12-14 gauge wire from the positive battery post to the wire coming from the fan motor.... This should be accessible after opening the hood.........

[70LongbedC20]

Originally Posted by GMC Jim

yes... the relay or the relay wiring is causing your blower not to operate on high speed. you might want to check the blower high speed operation..... just connect a 12-14 gauge wire from the positive battery post to the wire coming from the fan motor.... This should be accessible after opening the hood.........

Thanks for the tip. Will do exactly that, and see if the fan motor gets up to speed. If the relay itself is at fault, I suppose I could order that from LMC?

[Aarons72s]

I am not sure what yours is but is your truck a/c or non a/c? Only a/c trucks have the relay, and yes it is a pos. Heat trucks only have the resistor pack. So if you are only have a heat truck then the resistor pack is propably gone. But if you have a/c then it is probably the relay.

[70LongbedC20]

Yes, I do have A/C. So Relay, or relay wiring are the most likely culprits. Thanks for all of yalls help.