1976 Cadillac with no heat

[Ostara]

I had my '76 out this week and found that I have no heat. There is a sound that reminds me a bit of a child's party horn coming from somewhere under the glove box which will stop once I find whatever climate control setting she decides she likes at the moment. The air always comes through the heater vent regardless of the setting. sometimes it does move through the dash vents, but never the defrost vents (which I also needed...) Any thoughts? If it helps, the previous owner riped out the A/C system, so I have some plugged hoses under the hood and the compressor is gone, but I don't know if that would have anything to do with it. I will try to post pics in the next day or so. Thanks!

[bluke1]

The heater door is controlled by engine vacuum. The noise could be a vacuum leak. Get it to make the noise and look around beneath the dash. Follow the lines, it starts from the vacuum source (the engine bay) through the passenger firewall to a distributor, and splits off to other componants. Find a vacuum diagram and compare it to what you have.

[Ostara]

Thanks, I'm guessing that is at least why I can't get any air to the defrost vents. I'll have to find a diagram with the hope of not screwing things up further.

[Ostara]

Here is a picture of the plugged hoses.Hoses.jpgEngine 1.jpgEngine 2.jpgThe final two are in case anyone notices anything else missing. Thanks!

[Guest]

it looks like they completely by-passed the heater core. try hooking the hoses back up.

[northgahearse]

yes the heater core is by passed.
Take the hose apart at the clamp and run one hose to each plugged hose and hope it does not leak inside.
Vacuum does run the doors but it can be as little as vac line loose or as bad as the climate control PROGRAMMER being bad

also the hose running over the wiper motor them down by the back of the carb is the line that feeds the inside of the car make sure its hooked up

[hotroddwayne]

There's 2 reasons why someone bypasses a heater core:

1. When a heater core starts leaking inside the car, on the passenger's feet. It'll stink up the driver's compartment with the pungent odor of antifreeze and fog up your windows. Also saturate your carpet with antifreeze. Some leaks can be so small they only give off an antifreeze vapor.

2. The heat/defrost controls aren't working and you can't bypass heat from the inside of the car during warm months.


Those hoses are supposed to connect up to the water pump and intake to circulate antifreeze through the heater core. When you hook up the hoses... be prepared for one of the 2 fates I mentioned above...

My money is on a leaky heater core.

I know the 1980 & up to early 1990's (maybe even later) the heater core is easily accessable from under the hood... the heater box can be opened and the heater core replaced really easily from under the hood. Most heater cores have to be changed out under the dash from inside.

Let us know what you find out?

[bluke1]

I have the factory repair manual on my computer. It has all the vacuum and electrical diagrams, and how it all works. Is it legal to post up, if I knew how?

[Ostara]

Thanks for all the help guys I'll hook up those lines in the next few days and post my findings.

[Ostara]

I hooked the hoses back up and ran the engine for a few minutes. I checked the vacuum hose in the engine compartment and it is hooked up and appears to be in good shape, no apparent rot or cracking. I am happy to report that I now have heat and when I switched the thermostat to a cooler setting the air went back to cool and began blowing out of the dash vents. I still am getting nothing throught the defrost vents, so I'll have to find that vac line as everything else seems to be working so far. There was no smell of antifreeze, so I'm keeping my fingers crossed. Thanks again for all the help, there is much more to be done with her, but at least now I have a basic comfort for the cold months.