72 No blower on high speed

[67RS/SSx2]

1972 Super with AC. Blower works fine on low and medium. Does not work at all on high. Saw another thread that talked about a high speed fan relay near the glove box. Thought that would be my problem.

Looked, and saw a new relay there. So that is not likely my problem. What should I look for next? Is there a fuse for the high speed? I guess I need to find a wiring diagram for my truck!

Thanks!! This is a great site!

Dee

[it2castelo]

Make sure the relay itself is connected to a good ground. The relay enclosure is a metal box that needs a good ground because that is the hi-speed fan ground. Had the same problem but my ground bolt was way corroded. No ground, no workie.

[BlackTopMotors]

Check the switch. If working then check to see if you are getting power to the relays...I suspect the prob is still the high speed relay...the ground... or the wires to it. I use jumpers to connect the power blue/purple (high speed relay wires) to the blower (a black alligator clip in the pic) and then a jumper to connect the small orange to the blue/purple (a green jumper wire in my pic). Hope that makes sense. You should be able to get all three speeds...if so focus on getting the H.S. relay to work/cleaning, grounding it, hooking it back up or replace it.

Sometimes the prob is as simple as cleaning all the contacts (thinner, cotton swaps and a bit of sandpaper...(Ive revived a relay or two that way as well).

[67RS/SSx2]

Thanks for the replies!

There is a ground wire to the relay so I think it has a good ground but I will check that. However, the photos showing the wiring connections scare me. I only recall one wire connecting to the blower motor (but I could be mistaken, I am getting older you know).

I'll take another look to see what I can find. Thanks again!!!

[BlackTopMotors]

Don't let my pics put you off ...the additional wires are supposed to be inside the cab connected to the high speed relay...I ran them through when I was going through my wiring...When you pull the wires off the hs relay it should look similar if not identical. I just want you to be able to check that all speeds are available to the blower

[abrahamseven]

Dee, I had the same problem , that post you seen was more than likely mine. Anyway ,my blower only worked on high also and information from these good guys on this forum and me doing some research I found that the relay is only for the heigh speed, what controls the low and medium is the heater/AC blower speed resistor. I would guess that is your problem,

steve

[abrahamseven]

Dee I screwed this post up, what I wanted to say was the relay is for high speed only, so it could be relay or the switch. I have a new switch I could make you a super deal on.

steve

[Wrenchbender Ret]

There is a separate fuse for the high blower. It is usually at the junction block on the engine side of the firewall or the inner fender. It is in an inline holder. Often the ends of the holder get burned out due to the high amps. Like the guys say the relay must be grounded.

[67RS/SSx2]

Thanks for the clarification on the photo, BlackTop. I can breathe again now.

I had a chance to piddle a little tonight. Pulled the relay. It checks good. Switches when powered and the switch makes good contact.

The small orange wire to the relay coil gets power when the switch is in "high" so it looks like the switch is doing its thing.

When I jumper the purple wire to the blue one in the relay switch wiring harness the fan runs. But when I jumper the purple wire to the orange one in the same harness I get nothing. Seems the constant 12 v that's supposed to be on the orange wire is not there.

It looks like there is a fuse in the orange wire in the wiring diagram above. It's hard for me to tell as the diagram is a little small on my laptop and my eyesight is not quite stellar.

So next chance I get I need to trace out the orange wire. Where does that thing come from? Looks like I'll need to pull the glove box.

Where in the world is that fuse?

Anyway, I'm making great progress and I know I'll get it eventually. Thanks again to all who have chimed in. You are a great help and you're keeping me motivated to get this corrected!

[67RS/SSx2]

Duh!!!! Just looked at the wiring diagram again and saw that the orange wire comes from the fuse panel, connected to the Cig Lighter cavity. Guess I'll be looking at the cig lighter fuse next chance I get!

[stsalvage]

Originally Posted by BlackTopMotors

Check the switch. If working then check to see if you are getting power to the relays...I suspect the prob is still the high speed relay...the ground... or the wires to it. I use jumpers to connect the power blue/purple (high speed relay wires) to the blower (a black alligator clip in the pic) and then a jumper to connect the small orange to the blue/purple (a green jumper wire in my pic). Hope that makes sense. You should be able to get all three speeds...if so focus on getting the H.S. relay to work/cleaning, grounding it, hooking it back up or replace it.

Sometimes the prob is as simple as cleaning all the contacts (thinner, cotton swaps and a bit of sandpaper...(Ive revived a relay or two that way as well).

Not to say anything bad about your truck But I think its time for you to brake down and buy a new AC ans heater harness that looks like a mess and having exposed wires like that is never good for 89.00 you get a Brand new AC and heater harness From M&H wire harness I swear up and down about them factory repop wire harness and I replace all my wires in all my trucks any car or truck over 30 years needs new wires

[stsalvage]

Now to add about that relay looks don't mean **** i bought 3 relays and they all where bad I cleaned the old one and put it back in and it worked. Never count out relays on Old car's and trucks

I'm thinking of putting the AC controller in my 1968 3 door suburban that only has a heater the reason why I like to have the Fast speed and the switch on the AC unit is easyer to replace then the leaver is sence i just broke mine and i did some checking and it looks like it will work.I did see something strange on my 1971 Cheyenne 1/2.The ground for the relay has to go out5 side in the engine bay just below the blower motor to get it's ground then the black wire has to go back in side to connect to the relay then the relay connects to the Fiber glass heater case behind the glove box.thought that was strange but it works.


I have a 1972 deluxe 3/4 ton truck that just has the heater only wish i would of known that the AC harness was not part of the main Fuse harness or i would of just put the AC control unit in and add the AC harness and the one relay and its be done

it's strange that stuff like that can be made to work Only GM would do stuff like that

[67RS/SSx2]

Hallelujah!!!! (is that how you spell that?)

Traced the wiring back to the fuse box and found a wire not connected, but near the Cig terminal (no cigar fuse though). Plugged it in. Then re-installed the relay.

Rats! Still no high speed. Checked and I now had power to the orange power wire to the relay contacts. Found a bad connection at the power wire to the relay coil.

Plugged that in good and Presto! Now we have high speed blower.

Sill leaves me with one question. WHERE IS THE CIGAR FUSE???????????

Thanks to all who chimed in to help.