Heater blower motor will not work on high speed?

Yes there is a high speed relay which sounds like it is out. Here is a guide to help test it and the blower motor wiring diagrams so you can see how the system works with the relay location below as well.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Check out the diagrams (Below). Please let us know what happens.

I've already replaced the relay you refer to and the blower still does not work on high.

Thanks,

Jeff

Check the connector for signs of melting, could be the switch or the circuit to the blower relay.

Turn control switch to Hi and look for power at the hi speed relay orange wire-No power either you have an open wire or the blower switch itself within the heater/ac control module-

Also check AC maxi fuse 50amp-it powers the hi speed relay

I've replaced the blower, relay, blower switch, and blower resistor and still have no high fan speed.

Must be wiring between the switch and relay, maybe the ground.

Here's the electrical wiring diagram-try tracking it from the HVAC module to the blower motor-

Here is a possible solution for your 1995 GMC K1500 blower that wont work on high. First remove the glove box and set it aside. Now look into the area that the glove box resided. You will see a wire harness covered in factory foam and next to this on the right you will see a flat silver box that is your ECM. Now remove the foam covering gently because you will want to put this back on when your done. Now that you have removed the foam cover you will see a large junction connector and another connector with just a red and a black wire. Now what you want to do is turn on the ignition switch and the fan speed switch to high. Now gently grab ahold of the red and black wire connector and wiggle it if your fan came on you have found the problem. Now if this worked for you remove the positive battery wire from the battery because the red wire at this connector remains hot. next disconnect the connector and look into the female side of the connector the red wire will show signs of it being loose, meaning that it looks like it has melted, This is due to a loose connection. Now if you opt to get a new GM connector or you can tighten the female connector so that the pin will fit snugly into it once again. Once this has been done you can put the connector back together you will see that the connectors still move when plugged back together. To fix this you will need a zip tie. Now put the zip tie between the red and black wires with the connector back together. Now pull the zip tie tight and cut the long end off with side cutters. Now reconnect your battery and turn your ignition switch back on and fan speed switch on high. The fan should be blowing on high, now wiggle the connector one more time the fan should stay on without interruption. Now put that foam covering back on just the way you found it. Push the wiring back in like you found it and then put you glove box back in. You shouldn't have anymore problems with the fan anymore if this was your problem

Great addition to this thread! Please feel free to help out whenever you are on the site :)

Cheers, Ken

All 4 blower speeds work, but if I turn knob to off position and then turn back on it might not come back on. Or it could take 5-10 minutes and it will work again. I just leave it on lowest speed now and it works fine.
Got any ideas?

It sounds like a relay issue. Check under the hood for the blower motor relay and switch it with another one with the same part number to see if it fixes the problem.

Where approximately under the hood is the relay?
Thanks for your help.

There should be a relay box. IT will be a black plastic box and is usually mounted on the inner fender.

Under hood relay box has an AC relay that is a 4 prong relay and blower motor relay is a 5 prong relay. Any idea where else it might be? I'd rather not deal with the dealership.

Found relay behind glove box, right beside the resistor.

Pain in the butt to get to, but it's all good now.
Thanks for your help

Still having problems. Resistor and relay are good so was wondering if switch or pigtail located on and behind control panel could be the culprit. If pigtail shows burnt wires should I also replace switch?

Thanks in advance for any advice you might have for me.

Hey SIERRA GUY,

Is sounds like the blower motor is going bad, here is a guide that will help you find the problem.

https://www.2carpros.com/articles/blower-fan-motor-works-on-high-speed-only

Run some tests and get back to us so we can continue helping you.

Best, Ken

Y'all were right. Finally broke down and installed new blower motor. Pain in the butt to get 5th bolt out so just used 4 on new install. Works great and I've now got ac again.

P.S. Old one was dated Dec 1996, guess I was lucky it lasted this long.

Thanks again, Tom
Y'all are the best

Nice work, we are here to help, please use 2CarPros anytime.

Cheers, Ken