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My fan works on low, med, med high but not on high. Think it could be the blower motor relay that's mounted on the outside of the fan housing under the hood? '77 Monza 2+2 V8.
I've traced wires until I'm bushed (doesn't take much for an old fart) and that seems to be an unknown.

Well, that relay is cheap so I guess I'll just swap it out and see.

Mes' did you do any multi meter tests? Voltage at the switch before and after, at the blower itself? To really help we will need some blanks filled in. The wiring on the non A/C is pretty simple I don't recall any relays for that, now A/C that is a different kettle of fish! Harry

Sorry, been stuck working.
Well, it used to be an AC car but it's removed. I'm doing more voltage testing this weekend. this is a similar pic of the relay and it's mounted in the engine bay on the heater fan box. I've got one coming today as the one on there is super corroded. It's cheap so what the heck. After this weekend I'll get back on and let you know what I find. Hope voltage tracing or the relay leads me to the problem. Parking lights and all other lights work so I know the 12V is getting to the switch so I'll follow it to the dimmer and out from there next.

Well, new relay didn't fix it so when I get some time I'll start tracing wires from the switch and go from there. Almost got it ready for the exhaust this week so I'm coming to the end of the road with the rebuild.

If you have time check this post out. viewtopic.php?f=44&t=44075

generally, if it works at some speeds and not another (like your High speed here) its a fried resistor in the resistor pack .. one of them has overheated and is fried.

http://www.samarins.com/glossary/blower ... istor.html

https://www.youtube.com/watch?v=hgar6Q1lV6A

http://www.youfixcars.com/blower-motor.html

https://www.youtube.com/watch?v=UJ-MfAo8AUQ

https://www.ericthecarguy.com/faq/solvi ... ms?start=7

https://www.cargurus.com/Cars/Discussio ... 2_ds569146

good luck, Sav

It might be simpler to make your voltage checks at your new relay. Since your fan is working at the lower three speeds then your resistor pack is good. Looks like High speed uses the relay and does not go through a resistor.

With your fan switch in High see if there is voltage at the plug for the relay - orange wire 86 (looks like the middle two should be the coil). If it does have voltage then the relay is turning on and I would guess that there is no power at 87 (red wire) and that is why your high speed is not working (fuse link).

If the plug for the relay doesn't have voltage then there is probably a problem with your blower switch.

Of course I'm making assumptions here and if Zeke's schematic is wrong then it is his fault But I trust him, it looks good!

stage169 wrote: Zeke's schematic is wrong then it is his fault But I trust him, it looks good!

Zeke while your under the bus can you check the right rear brake it seems to be a little grabby! I think you may have a switch problem as well. Most likely I feel. Harry

Thanks, I replaced the relay and that didnt fix it so I'll check out the switch next. I appreciate the drawing too!!

None of my h-bodies have had A/C, so I can only go by the schematic. But my money is on the fusible link; easy to prove with a meter or test light.

My gawd that's a horrible drawing!