Blower Relay Hot! No HI Speed...

[cmg27]

On a '72 with factory air is it normal for the blower relay to get hot while in use? I noticed this while trying to figure out my HI speed not working. Weird thing is that I bought a brand new GM relay, installed it and it did nothing??? Didn't work on any speed. The new part looks exactly the same, just doesn't work at all. Anybody else run across this before? I'm assuming the original relay is bad as everything else works fine. LOW and MED speeds work, HI seems like it goes back to LOW. All connectors and wires look nice, nothing burnt or melted and all grounds are clean. Any ideas?

TIA

[Classic Heartbeat]

Where was the relay located that you replaced? The high speed fan relay is located next to the inside firewall. Mounted to the heater core housing. WES

[cmg27]

Wes,

Yes, that was the one. Mounted on the heater core housing far right side.

Thanks!

[bouncytruck]

Don't know about the relay getting hot, but my high speed doesn't work either. I've replaced the switch (twice), the resistor and the relay and still no luck. I guess the next step is the wire harness or the blower motor itself.

[jhow66]

Your high speed works off this wire from fuse panel. Check to see if it has 12 volts at all times. Also they get loose at fuse panel and heat up causing a corroded conection.

[Stocker]

When my high speed stopped working, it was just a bad switch... iirc, I got a new one from NAPA.

[Bob B.]

Yes, that relay has to be grounded. There is a ground wire in he harness going to the relay. It has a ring terminal, and should be under one of the relay attaching screws.

[cmg27]

jhow66, I don't understand the fuse box picture. The red wire I have is only for the cig lighter, although there is an unused female connector off of the same wire near the fuse box end. Is there supposed to be something plugged in there? I have no extra connections at the relay?

[paaw]

let me know, because I replaced blower motor, relay when I iput new relay in and grounded it to the glove box door, didn't do any thing on high, what it the wire by itself on the relay for, because low and med work when it is not hooked up of grounded. thanks in advance

CHico

[jhow66]

Originally Posted by cmg27

jhow66, I don't understand the fuse box picture. The red wire I have is only for the cig lighter, although there is an unused female connector off of the same wire near the fuse box end. Is there supposed to be something plugged in there? I have no extra connections at the relay?

That wire feeds both. Female plug is for some acc. Check the wire at relay to see if it has 12 volts. Trace this wire from fuse panel to relay. Does cig. lighter work? If it does, take a jumper wire and ground the relay to a good ground and try it.

For AC to work on high, all levers have to be to far left. When you put the fan switch in the "HI" postion this shuts a switch inside relay that connects the "red" wire from fuse panel to the "purple" wire that goes to fan motor by' passing the resistor for "lo" and "med". To check to see if your fan motor will run on high, disconnect the wire from fan motor and run a jumper from battery "+" to connector on fan motor. If it does not that is why your relay is getting hot. To me, it sounds like the relay is not grounded. Try this and let me know the results.

[cmg27]

jhow66,

So is the cig lighter end of my red wire supposed to have more than just the lighter connector on it? I still don't understand where the separate power is supplied from and I have no available terminals left at the relay. My relay has one connector of three wires, one single connector with a smaller size orange wire and the black ground wire with eyelet. Maybe my problem is at the other end of that ground wire, wherever that is? I'll try your suggestions and let you know.

Thanks for your help!

[jhow66]

Look at this diagram and see how the wires run. Plus read this thread. Will check mine out and see if I can make it easier for you.
http://67-72chevytrucks.com/vboard/s...wiring+diagram

[jhow66]

Got to go. Be back later .Need more info just ask.

[Baby John]

Well, I can't provide any info except to say that I have a Vintage Air system in our truck and though it will run on high for a short time, it will eventually heat up and the relay will kick off.

It won't happen on med or low. I felt of the switch when it shut off and the switch itself is really hot.

[jhow66]

cmg27 see if this will help any:

[cmg27]

Thanks for those exploded diagrams! I can see that the lighter harness is like mine, just a single red wire directly to the lighter from the fuse box that only feeds the lighter. In the first diagram I cant read most of the text, but appears to show an orange wire also plugged into the "cig" receptacle. I see no signs of that orange wire under my dash? Is there any chance that '72 is different than '71? You've been very helpful and I really appreciate it! Hopefully I can get this figured out! I have an original 1972 GMC service manual on the way.

By the way, my blower motor works fine at high speed, I jumped the wires at the relay and it went to high speed.

[paaw]

cmg27 what wires did you jump to make it run on high

Chico

[cmg27]

paaw, it was within the three wire connector at the relay. I believe the orange wire is main power and jumped to purple for high speed. Same as running a jumper wire from + battery terminal directly to blower motor. Be careful!

[jhow66]

Did truck come with AC? If so there should be a wire (red or orange-#12 gauge) running from the "cig" spot (cig will plug into the pigtail) to the relay. This supplies power to the relay and cig lighter at all times. When you move the fan switch to HI with all levers to left (for AC) it powers the relay to connect this wire straight to the wire going to fan motor. This way the fan motor gets a full 12 volts. Is all the spades filled on your relay? If so trace the large orange or red wire back toward fuse panel. It probley has been disconnected and stuck up in the tangle of wires under dash. Keep asking questions. Have wired cars from scratch making my on fuse panels and connections so should be able to help you find your problem. Just keep answering and asking.

[cmg27]

Yes, factory a/c. All spades at relay are filled. The orange 12 gauge wire is part of the harness/connector (3 prong) at the relay. Its factory wrapped and I havent tried to trace it yet. My red wire from the "cig" connector at fuse box goes directly to lighter and is a separate harness/wire by itself, feeds nothing else. It just sounds like a different setup than what you are describing. I'll take some pictures tonight or tomorrow and post them.

Thanks again!

[cmg27]

Here's a picture of a lighter harness like mine.

[paaw]

cmg27 have you tried unhooking your jumper wire, jumped min cut on high and then back to low did this three times, then tried it with out the jumper and now my high works with out the jumper

Chico

[cmg27]

paaw, I never left the jumper wire in place, just used it to test the hi speed that way. So you say that after jumping the orange & purple wire on the 3 wire plug three times it started working by itself? Thats interesting!

[paaw]

works like a charm, i guess the relay just needed a jolt, i grounded it to the inside glove box screw, tried it again while ago works fine

[cmg27]

Well, as it turns out the new GM relay was the wrong one and the original was definitely bad. Went to Napa today and bought another relay, put it in and everything works great. Doesn't get hot either! Cant always assume that you have the right part just because it looks right. Lesson learned.

Thanks to all for your help trying to get this solved!