bmichener

Hello, I bought a 1970 Cutlass Supreme "Holiday Edition" this past summer while in Florida and drove it back up to Washington, DC. I am new to this car and classic cars in general, so my knowledge is still quite basic.

While in florida it was hot, so I wanted to get the A/C working, I had the freon recharged and the A/C blew wonderfully for about 3 days. Then it started making a burning rubber smell, and my a/c guy said that the compressor was seizing up, so I stopped using the A/C until I can get it rebuilt or replaced. That was a few months ago. Now once it got cold, I started using the heat, avoiding switching on the a/c as I didn't want to completely seize up the compressor. It worked great for about two weeks and then the heat stopped blowing (I am getting no air from the ducts, or perhaps a very faint bit of air which is probably a draft).
Here are my questions.
1. How do I diagnose what is broken is there a fan that stopped working or does the heater coil need to be replaced? All I have checked is the fuses (which look fine)
2.Is this problem at all related to the a/c or separate?
3.Are the possible fixes simple (i.e by a new heater coil an NAPA and swapping it out real quick) or complicated enough that I should take it in to a mechanic. I have pretty basic tools available right now so I cant do anything too involved.
Thanks for your help,
Ben

Lady72nRob71

Blower circuit is pretty simple. Since no sppeds work, check the fuse in the fuse box first. Replace it; not look at it.
With blower on different speeds, check voltage at the purple wire in this picture.

If you cannot get to it, probe that same wire under the relay above the brake booster.

You can even probe some of the different prongs of the resistor to ground and report back your findings.
Resistor is the red thing with the 4 wires on it.

Since you smelled something burning (inside the car I assume) I think it was either the blower resistor or the fan motor. I bet the compressor is okay. You can unplug it (at the compressor) if you want until you find the cause of the problem..

455man

I'll be diving into this soon also as soon as I can get some nice weather.

Allan R

bmichener
keep in mind that in Robs picture, he has the inner liner and most of the right side AC parts out of the way when he was rebuilding his car's front end. So the wiring you see is NOT that easy to access, but the pic gives you a great idea of what you're looking for.
..and just so you know...Rob knows what he's talking about.

Lady72nRob71

Even with it all together, you MIGHT be lucky enough to be able to gently pull the purple wire out from under the fender. There might be enough slack. If not, then checking voltages at the high speed relay (under brake booster) or at the resistor.

bmichener

Thanks so much for the quick (and useful!) responses. What a great forum! It turns out that my visual check of the fuses wasn't sufficient. I replaced the fuse and got the heat to work - well mostly. I found that the Low setting and the two unmarked settings above low work fine, but that I get know air when I set the vent to high. This is obviously a very minor issue, but out of curiosity I wonder what would be causing it. I dont know if this is a new issue or if this has always been the case for as I mentioned earlier I havent had much opportunity to use the heating or cooling.
Thanks for all your help,
Ben

MDchanic

Not to be disagreeable, Rob, but I must disagree -
I think the burning smell was the compressor belt, trying to turn an essentially seized compressor.

If that is the case, then the "mechanic" probably pulled the compressor clutch plug to prevent further damage, and the compressor will need to be changed out in the spring when it's convenient. I just hope he didn't lose any of that precious R-12...

This is a common problem, Ben, and has been addressed here a number of times, in greater detail, if you'd care to search.

The High speed is on a different circuit than the lower speeds, because it draws so much current.

For the lower speeds, power goes through the fuse, through the dashboard switch, through the resistor block (in Rob's excellent photo), through the High Speed Relay (on the firewall), into the big purple wire, and to the fan motor.

For High speed, power from the dashboard switch turns the High Speed relay "ON," and power for the fan motor is then taken from a big red wire connected directly to the terminal post on the horn relay, and then flows through the purple wire to the motor.

If you've got a bad High speed, therefore, the problem is probably either a bad High Speed relay or a blown 30A High Speed fuse, which is in the big red wire between the terminal block and the High Speed relay (though, of course, it could be a cut wire, dirty connection, etc.).

- Eric