climate control 78 Caddy DeVille

[1958tk]

hi there, just bought a 77 Cadillac DeVille with 31,000 original miles, having problem with the heater or climate control. I move the selector and I do not hear any doors opening or closing as associated with vacuum canisters. The temperature control is getting a little air forced through it while driving at freeway speeds, changing the temperature has no bearing on the actual temperature you can feel. The only Blowers speed that works is clear to the right defroster, but it's blowing through the defroster and down below. Can't seem to find any information on the Internet on this problem. I think Cadillac way over thought their climate control system. Anyone have any suggestions? Thank you in advance.

[Cadillac Kid-CLC #15364]

Mr.58,
The first thing I would recommend is getting a factory service manual for your car, either an original or good reprint.  The system in the '77s is a simple system when you compare it to a 2010 computer operated system.  However, in order to provide "Automatic Temperature Control" it is necessary to control the cooling, heating, fan speed and air outlets.
If all the vacuum actuators are functioning correctly you shouldn't hear them operate.  I would suggest that since the fan works when you place the selector in Defrost and I am assuming you checked the fuses, either a loose connection or a bad AC re3lay (on the engine side of the firewall near the heater/AC Evaporator box) might be the first place to check.
Greg Surfas

[CarFreak]

I am assuming you checked the fuses, either a loose connection or a bad AC re3lay (on the engine side of the firewall near the heater/AC Evaporator box) might be the first place to check.
Greg Surfas

That's what was wrong with the Climate Control on my 1978 Brougham d'Elegance.   


If not, be sure to check out this Cadillac Service Roundtable Training brochure hosted in our Documents Section:   
http://www.modifiedcadillac.org/documents/1970s/1977/1977%20Roundtable%20AC/

[73eldo]

If the blower kicks to high only on defrost its the temp sensor in the head behind the alternator.  Its a single wire sensor that often gets the wire knocked off it.  It grounds to allow the blower to come off low for heat modes so you can just touch the wire to ground and see if the fan kicks on.   There is an identical looking sensor on the rear left head.  The rear one turns on at like 270* for the stop engine temp light.  The one behind the alternator turns on at 120* so you can imagine if they got swapped there would be issues.  I think there are also a few other variants but those were the only 2 that would have been originally on a engine from that era.

I cant remember but some years the blower wont run at all unless there is vacuum to the system.  Other years it will run but lots of stuff wont work right.  On most that I have messed with its the same vacuum line that feeds the parking brake release that feeds the climate control.  In that era Im thinking that line goes through over by the steering column but I am not sure about that.  Just remember working on something and damaging the line.  I figured I could live without the parking brake release but then noticed that the blower didnt run.  Just cant remember which car that was.  

[r schroeder]

Being the owner of a 78, I would do what Greg said, and get the manual. You will need both the 77 and 78 manual. The 78 is a supplement to the 77 manual.
 There are pages of testing info in there. It is the easy way of doing things. Ebay has these manuals all the time.

Roy