dhowe

Hello everyone. Visiting my dad for Christmas my heater stopped working. Since I purchased the car the blower had only worked in in the highest position, now it doesn't work at all. I assumed the switch had gone bad so I read out all the pins on the back of the switch for continuity and found none. Before I took the dash apart to try to replace the switch I read out the wires behind the switch and tried to jump the 12V across the wires to test the heater. That didn't work either. I am quite a newbie but I assumed either the switch or the motor had gone bad, and because it was kind of broken before I figured it was probably the switch. I checked the fuse and it was fine. When I moved the heater switch from the high to medium position I noticed what sounds like a relay clicking. I was trying to find a wiring schematic online and found this marvelous forum which led me to this post...

https://classicoldsmobile.com/forums...tor-speed.html

So I think I am a little over my head. I have a spare blower motor I got from the original owner. I don't really know what to do at this point, I can't see where the blower is and I have no idea what an 'air plenum' is. That post is about a 69 cutlass but I figure its probably similar. Could someone please give me some advice, if possible I would like to fix this myself. If I can't fix the defogger by Monday I get to drive 200 miles home with the windows open in the rain and snow.

Thanks for you help!

kevinkpk

Blower motor on high, runs straight off what the battery or alternator are putting out, check for a fuse. If it didn't work in anything but high before, there is a relay on the firewall that probably is the culprit.

Plenum is located on the firewall (under the hood) I am thinking passenger side, blower motor will set inside it with a ground strap and a single wire plug. Blower motors aren't that exspensive.

I had the same problem with my car, replaced the relay (motor was fine but 37 years old) replaced the motor, checked fuse, good. Still wouldn't run, I found the fuse holder was bad, replaced it, and all is well now.

The relay switches to a set of different resistors to get varible speeds from the motor, but in high, thats bypassed and straight (through a fuse) from the alternator. Fuse is probably an inline fuse, so check for it from the positive side comming from the battery.

2blu442

The heater fan on my 1971 quit recently and it turned out to be dirty contacts on the relay switch under the hood. I don't remember if the 1970 is in the same location, but 1971 and 72 it's behind the power brake booster on the drivers side firewall. You might try that as it's an easy thing to check. Good Luck! This isn't the time of the year to be without a heater fan! John

J-(Chicago)

When my heater control valve stopped working. I used a power inverter in the cigarette lighter and a $10 space heater for a week.

Olds64

That is a pretty cool idea J. You would have to own a pair of brass ones to do that.

You might check the resistor in the air plenum. It controls the fan speed with three different resistors. They fail often and the fan usually will only run on one speed, but if all of the resistors blow you won't have any fan at all. The resistors are all together and are bolted into the air plenum. When you unbolt it there will be three seperate windings of wire sticking in the air flow of the plenum. You should be able to get one from any older GM car. I think they used the same set up for about INFINITY years.

ozoneblue

Try using a jumper wire from Battery + to motor to test it then follow harness back across firewall there are several connections that go bad over time . If motor works off jumper wire put a in line fuse in it & drive it home.

dhowe

Thank you so much! By using your suggestions I found the inline fuse and it was burned out. I replaced it a few times but it kept burning out, I got my dad to hit the switch for me so I could investigate and look for a short. Turns out my blower motor has a bad bearing or maybe the fan itself is stuck on something as it makes a grinding flapping noise and then burns the fuse. I am about to open up the air plenum and investigate in there. Thanks to you all I am sure I will figure it out in time. Thanks again! I will update again when I finish.

kevinkpk

Good, thanks for posting a reply. You can remove the blower from the motor, and as I stated earlier, blower motors aren't that exspensive. I think mine was under 30 bucks. Mine uses a 30 amp fuse, you might want to verify what you have also. You certainly can tell if the motor is locked up after you pull it out.