Heating and air conditioning problem 1975 Cadillac Sedan DeVille

[Tomy]

Hello to you all,

I take the liberty of publishing this little message on this site. If it disturbs you, I'll delete it.
I am 23 years old and I live in the south west of France. About 4 months ago I bought a 1975 Cadillac Sedan DeVille with only 25,000 miles on the odometer. In absolutely impeccable condition!
Everything works wonderfully well on this car except for the cabin ventilation system.
Let me explain:
The ventilation works without a hitch. But when you put it on the coldest setting, the air is lukewarm, and the same when you put it on the hottest...
The air-conditioning fan works without a hitch, and the heating radiator was changed by the previous owner no more than 5 years ago...
He told us about a valve that might have to be changed, which would be the cause of the problem. The valve is located on the windshield side of the engine compartment, and is a sort of air "mixer"...
Do you think that's where the problem lies?
Do you have any other ideas?

In France, Cadillac vehicles are extremely rare, so it's hard to get any information. 😅 that's why finding this site is such a relief!

Thank you for reading my message!

I wish you an excellent day,

Best regards
Thomas

[Roger Zimmermann]

Thomas, if you don't have it, buy a factory shop manual. Available at eBay or at Faxon : https://www.faxonautoliterature.com/Search?categoryId=40326&keywords= You'll have to buy the '74 manual + the '75 supplement to have a complete set. No Chilton, they are just good to change the oil.
One member from this forum, Tim Groves, is selling a simplified booklet over the A/C from those cars, allowing to do some tests with basic tools.
If you are not knowing those A/C systems, you will have trouble to diagnostic the fault(s) from your car without the proper manual. If you have an A/C specialist in your region, ask him. He may be afraid because it's a Cadillac, but A/C systems from European cars are functioning with the same basic systems.
Some questions: do you know if the system has enough refrigerant? Is the compressor turning when you request A/C? Are all vacuum hoses in a good condition? Does the parking brake releasing when you put the shift lever out of Park?
Good luck!

[TJ Hopland]

Has this car been converted to right hand drive?  Just thinking that could come into play since much of the climate control is on the right side. Others in Europe may have to comment on how they move or modify things that get in the way of a conversion.

The valve they may have been talking about is often called the water control valve.  Its not used as a mixer, its an on or off for more extreme conditions so I don't think its likely your issue.   Some cars that is used as the mixer so it was reasonable for someone to guess that.

[Roger Zimmermann]

Has this car been converted to right hand drive? 

The car is in France. Why should have been converted? Only the UK is driving on the wrong side of the road!

[Tomy]

Thomas, if you don't have it, buy a factory shop manual. Available at eBay or at Faxon : https://www.faxonautoliterature.com/Search?categoryId=40326&keywords= You'll have to buy the '74 manual + the '75 supplement to have a complete set. No Chilton, they are just good to change the oil.
One member from this forum, Tim Groves, is selling a simplified booklet over the A/C from those cars, allowing to do some tests with basic tools.
If you are not knowing those A/C systems, you will have trouble to diagnostic the fault(s) from your car without the proper manual. If you have an A/C specialist in your region, ask him. He may be afraid because it's a Cadillac, but A/C systems from European cars are functioning with the same basic systems.
Some questions: do you know if the system has enough refrigerant? Is the compressor turning when you request A/C? Are all vacuum hoses in a good condition? Does the parking brake releasing when you put the shift lever out of Park?
Good luck!

Thanks a lot for the info!
Yes everything seems to work fine the fan works well and the engine compartment is like new... all the hoses are in very good condition...
I had thought about the refrigerant level... but in that case the car would be hot but not cold...? But that's not the case here...
Quite a strange situation...
Thanks for the link! I'm going to get these books and see if I can do something about it!
There's a garage not far from where I live that specializes in American classic cars but the problem is... you know when you drop the car off but you don't know when you're going to pick it up...
I'll keep you posted!
Thank you again for taking the time to help me.

Thomy rizet

[Tomy]

Has this car been converted to right hand drive?  Just thinking that could come into play since much of the climate control is on the right side. Others in Europe may have to comment on how they move or modify things that get in the way of a conversion.

The valve they may have been talking about is often called the water control valve.  Its not used as a mixer, its an on or off for more extreme conditions so I don't think its likely your issue.  Some cars that is used as the mixer so it was reasonable for someone to guess that.

No, no, no! The car is in factory condition!
But the dashboard has, I think, been removed to fit a modern car radio in the glove box.
Could this be due to a loose connection? Or perhaps it was done incorrectly?
The ventilation control works fine, but the temperature control doesn't. Is this an independent connection or not?

Thanks again!

Thomy rizet

[Roger Zimmermann]

It could be a disconnected temperature sensor (especially if the dash was removed). If your system is similar to the one in my '72 de Ville, the heater valve is usually open. If vacuum is applied, the water flow is stopped.
As the A/C system is not the system I know the best, I will not do stupid suggestions...You have to be documented and check if all elements are working as intended.

[TJ Hopland]

If you are in auto and turn the dial to 65 does the air come out the dash?  Then to 85 does it switch to the floor?   If you go to defrost does it blow on the windshield?    If it does all that that is a good sign and much of the control system is working.