1976 Eldorado A/C problems

[flw004]

Hey brother's, my Eldo A/C only blows HOT air through the bottom vent.  When I move the temp to 60 degrees the compressor comes on, however, no air blows through the top vents.  Only HOT air through the bottom vent. 
Any help would be greatly appreciated.

Thanks,
Fritz

Thanks, Fritz

CLC 22666
1941 Toure Sedan
1960 Coupe De ville
1965 Coupe De ville
1976 Eldorado

[Guidematic]

The first thing I would check is to make sure the system is getting vacuum. Often the line that provides vacuum can become detached/worn/broken.

Mike

[Gene Beaird]

What Mike says.  Check that you are getting vacuum to the climate controller first.  If you've done any work under the hood, make sure you haven't bumped or crossed anything. 

After that, make sure someone hasn't kicked the electrical connector on the climate controller.  I don't know where it's located on your car, but on our 79 Seville, it wouldn't be a stretch for someone to accidentally stick a toe in the connector and knock things loose. 

Anything else will require more in-depth troubleshooting, but these two quick checks will resolve most issues with the HVAC system.

["Cadillac Kid" Greg Surfas 15364]

Fritz,
The first clue is when you said "When I move the temp to 60 degrees the compressor comes on".
Unless it is colder than 30 degrees outside,OR someone has modified the AC controls, the compressor should be running at any time the ac selector lever is in anything but "off" or "economy".
My first question is did the system ever work, or is that the way you found it when you first got the car?
The Automatic Temperature Control (ATC) control systems are complex but simple, and typically tracing all the wiring circuits and vacuum circuits will reveal where the problem is.  You do, however, need a factory service manual with it's diagrams, and control descriptions to verify the system is correctly configured.
One quick check is checking the wires to the in car sensor.  That is the sensor that is located in the top of the dash pad.  If the dash was removed and the sensor damaged, or not re-connected, the system will go to full heat.  It is the act of a contortionist, but looking up through the hole in the top of the glove box insert, you should be able to see the sensor and it's connection.  There is a rubber tube running from the back of the sensor to the Heater box which draws air past the sensor so it can sense in car temperatures accurately.
Let us know what you find.
Greg Surfas

[Gene Beaird]

This was one of the things wrong with the HVAC on our 79 Seville.  The in-car sensor was disconnected.  Luckily, it was still in the car, but not hooked up.  After I got things actually working, and hooked up properly, all I got was nice, HOT heat.  After one of this list members mentioned the 'fail safe' configuration for these things when the temp sensors 'fail', is to go full heat, I started looking.  Oddly, the top dash was completely unscrewed from the dash, just being held in by gravity and the lower dash when I got the car. 

Pulling the upper dash is the only way you are going to get to that sensor, even if you can see it.  At least that's the way it was on our 79 Seville. 

i]When I move the temp to 60 degrees the compressor comes on[/i]".
Unless it is colder than 30 degrees outside,OR someone has modified the AC controls, the compressor should be running at any time the ac selector lever is in anything but "off" or "economy".
My first question is did the system ever work, or is that the way you found it when you first got the car?
The Automatic Temperature Control (ATC) control systems are complex but simple, and typically tracing all the wiring circuits and vacuum circuits will reveal where the problem is.  You do, however, need a factory service manual with it's diagrams, and control descriptions to verify the system is correctly configured.
One quick check is checking the wires to the in car sensor.  That is the sensor that is located in the top of the dash pad.  If the dash was removed and the sensor damaged, or not re-connected, the system will go to full heat.  It is the act of a contortionist, but looking up through the hole in the top of the glove box insert, you should be able to see the sensor and it's connection.  There is a rubber tube running from the back of the sensor to the Heater box which draws air past the sensor so it can sense in car temperatures accurately.
Let us know what you find.
Greg Surfas

[flw004]

Hey guy's I replaced a few vacume hoses on my 76 Eldo.   Now the A C works great for about 15 to 30 minutes.  Then the A/C goes away from the top vents, and hot air begins to blow from the bottom vent.  The compressor keeps pumping along, and the climate control changes speeds.  But nothing cold from the top vents or the bottom vent.  What a bummer.  You Guy's are the best, hope you may be able to help me out. It's hot in So. Cal
..........Thanks

["Cadillac Kid" Greg Surfas 15364]

Fritz,
If the AC works correctly for 15 to 20 minutes and then "goes away" and this re-occurs every time you start up the car (from, cold), I would suspect you have a vacuum source that is going away and I would suggest taking your shop manual and tracing all the vacuum lines down individually to correct the problem.  It is also possible that you have a poor connection in the sensor sting that "opens up" the circuit after it has run for a while and warmed up.
The good news is that if the system operates correctly for 20 minutes all the major components are most likely functional.
Greg

[flw004]

Thanks Greg, it's a good start.  I'll start poking around the vacume lines.

[flw004]

Hey guy's, just thought I'd give you reply on my A/C issue.  It's been resolved, thanks to the smarts here at CLC.  The problem turned out to be the controller located behind the dash.  The servo electronics was kaput.  I Located a controller by luck, on Ebay.

Thanks for the input....... 

[Scot Minesinger]

What Greg says and...The vacuum source that tends to be compromised after car is warmed up is the EGR valve failure.  You can easily check this by plugging the vacuum line to it.