1960s 1968 automatic climate control

[Cameron4725]

So I recently bought a 1968 Coupe Deville with automatic climate control. The guy I bought the car from said that the AC didn't work. So I was investigating to see if the compressor had a leak or if it would hold any refrigerant pressure, which it did. Then I noticed that the AC compressor is unplugged. So I plugged it in and it kicked on. However they're right below where you put the refrigerant in it was icing over but above that it was still warm so I think there is a blockage there of some kind that needs cleaned out. So I unplugged the compressor again until I have time to clean it out. However I turned the climate control to the hottest temperature to try the heat and it really wasn't blowing out hot air. Any ideas as to why? Does the AC compressor need to be plugged in for some reason for the sensors to allow the heat to come on? Any feedback on any of this would be greatly appreciated since I'm still learning about how this system works.

[kyle242gt]

I'm only barely getting into my 67.  But I have on good authority (a good buddy who's a pro auto AC tech from back in the day) that these systems can be finicky due to the electronic controls for all the vacuum shenanigans going on.

I suspect that the behavior of the compressor is okay, one side will be hot, the other will be cold.  And my buddy told me that the compressor being plugged in is not required for heat to work properly.  But the engine does need to be running and up to temp.

The FSM has a ton of info and flowcharts and so on.  Hope you get an easy fix; the water temp control is supposedly a weak point.

[Julien Abrahams]

There is quite an easy way to check if you get heat for the CC system. When you disconnect the vacuum line that comes from the transducer and cap that off, you can put the vacuum line that goes to the vacuum storage tank directly on the power servo. This will give maximum vacuum to the power servo causing it to move to the max heat position. The blower should go to high and warm air should be coming from the floor vents.
Note that it is important that coolant temperature is higher than approximately 120 degrees.
It does not matter thtat the AC compressor is not running.
The reason why it was not blowing hot air could also be due to the temperature inside the car. By connecting high vacuum to the power servo you bypass the electrical and vacuum circuits so to speak.

[cadillactim]

There could be a few items that won't allow the system to go to heat. So a simple answer cannot be given.

The factory shop manual can help, but requires a special tester most people do not have.

I have written a much easier to use manual that explains how the system works, how to test each part, and then how to troubleshoot it.

Tim

["Cadillac Kid" Greg Surfas 15364]

Cameron,
As Tim says, the FSM has a wealth of information regarding your ATC system. OI shows all the components and describes their functions. There is also two diagnosis Matrix's. One for the refrigeration system and one for the control system. The first step in diagnosing a "new" (to you) system is determining if all the components are installed and installed correctly, as well as verifying that all wiring connections are good. Vacuum lines should be traced out to determine, again their integrity and correct routing. On your car just a single vacuum leak or incorrect vacuum line connection can lead to all sort of symptoms, so they should be checked out first.
In regards to your initial question regarding the compressor being hooked up the answer is no. It is independent of the heating system, but it sounds (and this is a SWAG) that someone may have done some jury rigging in an attempt to improve or correct a defect in the refrigeration system and the controls may be driven to a permanent "Max Cooling" position (which doesn't cool since the actual problem was not addressed).
I would get the Factory service manual, check out the vacuum and electrical lines and go from there
Greg Surfas

[cadillactim]

Even though the factory manual contains a lot of general information, what it doesn't have is specific information on real world problems, especially when the car has been in use for a long time.

At the time of the 1968 factory manual's writing the Cadillac climate control systems were only four years old, so real world problems weren't really evident yet.

For example, a common issue is having to place the dash control lever in ICE to get the fan to come on. The factory manual makes no mention of this very common real world problem. Why? Because this problem developed over time and did not exist at the factory manual's time of writing.

In fact, the most common problems with these systems are not even mentioned in the factory manual!

My experience has shown that most people who have never worked on these systems will readily admit the factory manual doesn't really help them much. I can say this because I have had dozens of seasoned mechanics tell me this when they call asking for guidance.

Once someone understands the fundamentals of these climate control systems they can work with the factory manual.

But if someone is unfamiliar with these systems they will eventually become frustrated with the factory manual.

This is why I wrote my manuals in the first place, to make these intimidating systems easier to understand and troubleshoot.

Because for every person who can figure this system out with just the factory manual there are 10 who can't.

And that's just the reality of the situation.

[Cameron4725]

How can I get one of your manuals that help explain how the system works because I have a factory service manual, but as you said it is very helpful with trouble shooting.

[cadillactim]

You can email me directly at tagroves@wctel.net or call me at the shop at 864-348-7732.

Tim

[kyle242gt]

You can email me directly at tagroves@wctel.net or call me at the shop at 864-348-7732.

Tim

FYI - the manual is not a freebie:

The manual is $45 plus $10 US shipping. If you want one you can pay the $55 by PayPal using this email address, call with your credit card or send payment.
Tim
864-348-7732

Not sure if this is okay per forum rules, but seems a bit contrary to the purpose of a forum to post saying "It's hard to fix, but I know how" without coming right out and saying he's charging for the information.

[35-709]

Cadillac Tim is, and has been for a quite some time, an invaluable source of AC information (as has Greg Surfas) and repaired parts.  He has several AC manuals for various iterations of the Climate Control system and has had them available for sale for a long time.  If you have a specific question, post it here and Tim will answer it here and always has, he is available on the phone (leave a message, he will return your call) to help answer your questions. Troubleshooting from a distance, however is always a crapshoot.  If you want a manual that you can consult to better understand your system and its problems, plus easier ways to diagnose and fix them for the inexperienced like myself and many others of us, you want the Cadillac Shop Manual AND Tim's book for your year car.  The older these systems get and the fewer people there are that understand them, or that will even try, the more we need people like Cadillac Tim and Greg Surfas.   I have one of Tim's books for my '73 and he has spoken to me on the phone on more than one occasion to help me out.
 
He has taken the time and effort to write and have printed his AC guides and they are (in my opinion) worth every nickel he charges.

No, I am not related to Tim or Greg, nor do I work for either of them.   
Geoff N.         

[Larry Savino]

FYI - the manual is not a freebie:Not sure if this is okay per forum rules, but seems a bit contrary to the purpose of a forum to post saying "It's hard to fix, but I know how" without coming right out and saying he's charging for the information.

I can tell you this,He is not here to sell his books, Had I seen this post earlyer I would have suggested he purchase tims books as it walks you thru a very complicated system . His books are worth more then he Charges. Once you use one of his books you will also be refering other to use it ,

[Will68]

In the '68 the A/C compressor is either off or on.  The compressor is on in all positions except vent and higher dialed-in from dashboard control heat temperatures.  The problem is likely in the servo, the twin-disk assembly therein where the twin discs become warped or scratched over time and when you position the dash setting for cool the servo setting disc assembly matches that (via the transducer - 'cigar' cylinder under passenger kick well).  If the servo-side assembly has any vacuum leakage (due to warping, scratches, etc) it will not pull the vacuum servo motor/doors into the their full positions hence the perception that system is improperly working.  Resolution:  take the servo motor assembly out (easy), gently take out the two-discs and put through ultrasonic cleaner then sandpaper at 2000 grit to polish the surfaces, reinstall with tad-bit of vacuum grease.