1968 CDV Climate Control...no heat.

[Steve W]

I did a seach, and although here, and in "modified", I find some great articles about the climate control system, I did not find any mention of my specific issue.
My system pumps out cold air nicely. The a/c unit seems to work just fine. The blower works fine throughout the speeds, and the defroster works fine, both speeds.
However, the air temperature always seems to be the same, no matter what temp I dial up on the wheel...always cold...which is a blessing being here in Los Angeles! However, winter is coming and I would like to be able to turn on the heater as needed.
So...I'm looking for advice as to where to start looking. Anyone?

Thanks,
--Steve

[Kevin Wiles]

do you have a good heater core?   is the door opening from the heater core? if you listen you'll hear it open up.

[Steve W]

I can not tell...but remember, on the 68 CDV, I do not have a "heat" setting...just the wheel that is supposed to make the system add either heat or cold to maintain whatever temp you set it to. So, to activate heat, I put the dial on 85...but I feel no change in the temp. Tried it for about a half hour last night out driving around....no heat, in fact, no change in the temp at all.

Where do I listen for the "door" to the heater core? Obviously it will have to be either loud enough, or distinctive enough, for me to hear it over the enging running, right?

[Steve W]

OK...I was under the hood while my g/f played with the climate control...65....85....etc....and I found the servo arm that opens and closes the heater core door, I guess. It was moving back and forth as she was changing the temp...but it didnt seem like the full range of motion. So I disconnected the arm that comes from the servo thing...and by moving the arm left and right, she felt the temperature go from cold to hot inside the car. OK..so that works!..But when I hook the arm back up to the servo unit, it doesn't go far enough to open the door to allow enough heat inside. There is an adjustment of sorts, but not enough.

So...what do I do now?

[Otto Skorzeny]

Is that a wire/cable control?  If so, it sounds like it's binding or getting too much slack. Movre the leveer and wath the cable over its entire length.

[Steve W]

No, its vacuum controlled. Apparently, vacuum controls the movement of the arm. And its a pretty complex system. The Climate Control feature was an option, so not all cars had it. I haven't taken the thing apart because as I am reading everything I can find, it seems like they dont have a replacement for it, and I'd hate to accidentally mess it up beyond repair (as occasionally happens when I take stuff apart to "fix" it! LOL)

So...the individual parts SEEM to be working. And I am relieved that the heater core and door that opens or closes the heat works fine. With the arm disconnected from the servo unit, when the arm is all the way to the stop to the passenger side of the car, the ac is blowing ice cold. When the arm is all the way to the driver's side, its blowing hot air! Good!  So its just the vacuum controlled...whatever...that moves the arm that seems to be the culprit. It IS working...it just doesn't allow the full range of motion.

So...ideas?

["Cadillac Kid" Greg Surfas 15364]

Steve,
Automatic Temperature Control (ATC) was featured on Air Conditioned cars from it's introduction in 1964 on.  During the first few years up until about 1972 they made multiple modifications to the control systems.
In order to correctly diagnose a controls problem, and that is what it seems you have , since both the cooling and the heating, according to your posts work.
In order to diagnose these systems a component by component check is mandatory, and to effectively do that, you need a factory service manual for your year Cadillac.
In the manual you will find descriptions of the components, how they function individually and as a system, as well as several diagnosis matrix's.
Get a shop manual before you take anything apart.  You will be glad you did.
Again it sounds like controls, and before you can effectively diagnose it, you need to know more about the specific system and the functions al all components.
Looking forward to hearing how you braved the dark of a California Winter with your heating system,
Greg

[Steve W]

I DO have a Factory Service manual. It does not give me an exploded view of the servo unit internals however.
After my last post, I noticed something else...when I put the lever over to "Defrost" it does, in fact, increase the fan speed and temperature and directs all the energy to the windshield...so that works fine too!
I notice that it also pulls the heater core door lever even farther to the driver's side (open, or "hot")...as it should...and as it SHOULD when I turn the temp dial up to 85.
So...it all seems to work, its a matter of some type of internal vacuum adjustment....or maybe the dial or amplifier itself? I'm not sure. The Factory Service manual did show an adjustment of the servo arm to heater door...but that didn't do it.
I know I'm close to figuring it out, but there are just SO MANY complicated pieces to this puzzle...

[Glen]

Steve, do you have a hand vacuum pump?  If so disconnect the vacuum hose on the power servo and attach the hand pump.  Pump it down and see if the power servo holds a vacuum.  I think you have a leak in the diaphragm for the servo. 

The basics of the system are that the temperature sensors and the temperature dial provide an input to the amplifier which in turn sends an electrical signal to the transducer.  The transducer varies the vacuum signal to the power servo. 

The power servo controls the blower speed; switches the various vacuum signals and positions the temperature door. 

All the air that flows through the system goes through the A/C evaporator and is cooled to the max.  The air than goes through the heater core or bypasses the core and the temperature door controls how much air bypasses the heater core and how much is reheated. 

No vacuum on the power servo puts the system in max A/C and a high vacuum puts it into max heat.  I do not recommend you put full engine vacuum on the power servo because that might damage an otherwise good diaphragm. 

I think what is happening with your car is the power servo diaphragm is leaking and the transducer is not able to keep up with the leak so the system can never go into heat mode. 

Glen

[bill henry]

this may be an idiot question but does your 68 have a vacuum actuated hot water control valve like my 70?

["Cadillac Kid" Greg Surfas 15364]

Steve,
If I understood the information on a few of your posts, when you move the temperature dial from one end of the scale (65) to the other (85) the fan speed changes and the arm extending from the vacuum power servo moves.  If this is the case then it appears that at least the vacuum signal to the servo is functional, indicating that the control circuit appears to be working.
If the above is accurate I agree with Bill's premise that you MIGHT have a problem with the vacuum operated heater water valve.  Check you shop manual diagrams to see if the valve opens or closes on a vacuum signal.
Also, just for laughs, check your heater supply and return hoses for an extra shutoff valve in the line. If you find one, open it.  If the heater control valve requires a vacuum signal to open, first check ALL the vacuum lines from the valve back to the power servo head for either cracks, disconnects or other possible causes of a leak.
Let us know.
Greg

[Steve W]

OK...I think we're on to something here.
And here's where I AM lucky....seems like every component works.

Its down to just ONE THING...the lever that opens the heater core door and the servo that controls it.

When I have the controls set to defrost, the servo pulls the arm all the way to the left (or driver's side) to put max heat to the windshield as it should! Perfect...toasty hot!

However, when I am in "auto" mode, and turn the dial to 85, it should do the same thing, pull the lever all the way over to allow max heat to enter the car, and it does not. The servo does not pull the lever far enough over, even after I adjusted it, to get the heater door to open all the way. It does move, just not far enough.

SO...I THINK its either a leak it the vacuum circuitry of the servo unit in the heater mode...or the head unit electronics. Maybe even though I am putting the dial on 85, internally it isn't reading or even selecting 85 as a setting.  (Did I describe that right?)  In othere words, the dial is off-kilter somehow and even though I THINK I'm dialing up 85, the internals are not matching up to what's on the dial.

But if any of you have ever looked at the 1968 CDV Service manual section for the climate control section...good lord! Its like reading a script to an old Danny Kaye movie..."the vestle with the pestle and the potion with the poison..."  (OK, I know,,,a REALLY obscure reference! LOL)  Totally confusing,,,

["Cadillac Kid" Greg Surfas 15364]

Steve,
Beside the fan speed control via the "wipers" the main servo only moves the temperature door directly.  The selection of  "defrost" via the lever on the control head rotates a (I believe it is 9) 9 port vacuum valve which then sends the vacuum signal if all the lines are correctly connected and there are no leaks, to the auxiliary actuators shown in the service manual which then in turn operate the Mode doors, the vent doors, the heater valve, etc.  Your vacuum diagram clearly shows the vacuum paths for the various modes of operation.
Look for the vacuum leaks and make sure the vacuum control lines are ALL connected correctly.  You do this by following each line and comparing it to what the Service manual shows.
The most common thing I have found working on "new" cars is that someone has recircuited the vacuum lines or plugged them off in some attempt to re Engineer the systems.
Greg

[Glen]

Steve is right, it is possible the dial maybe misadjusted or there maybe a bad resistor in the string.  The ambient sensor, duct sensor and in car sensor are in series with the temp dial.  If any of those are bad the amplifier won’t send the right signal to the transducer. 

There is a resistance chart on page 1-25 of the shop manual.  Check the sensors against the chart.  If they are OK then it might be the resistor on the dial. 

Glen

[R. Scot Minesinger]

Hi, I have a 1970 Caddy and I got my climate control working real well.  It sound like your servo is bad, not the linkage because you get heat in defrost.  It could also be your dash unit, but more likely the servo unit.  USA Parts 1-304-724-6600 sells re-built servos that work.  I replaced mine and it was done in about 20 minutes.  Make sure every single vacuum hose in egine bay and under dash is replaced too-they make look OK, but after more than 40 years they are not.  Plus after I replaced every single vacuum hose my engine is so smooth.

Good luck,

Scot

[DinoBob]

IIRC from my experience with my old '68 Fleetwood, selecting defroster will always actuate the arm, siince it "pins" the resistance in the circuit at infinity...this is 20 odd-years ago so I do not recall for sure, but I would suspect the temp dial.

[Steve W]

You guys notce that in the shop manuals there are all kinds of "special tools"? In the section on climate control there is a special tool for the temp selector dial....where in the world wouid I get one of THOSE???

["Cadillac Kid" Greg Surfas 15364]

Steve,
The nuimbered tools WERE avaliable through Kentmoore Tools back when the cars were new.  Many of them still are in SPX Kent-Moore listings.
Greg

[Steve W]

How do I find them Greg?

[35-709]

One place I see Kent-Moore tools for sale (used usually) is eBay Motors.  Also Google "SPX Kent-Moore"(without the quote marks), that will show you where and how --- if they are available.  A good AC shop may have what you need to borrow, sometimes, usually shops won't loan tools unless they know you well (I stay tight with my AC guy).
Geoff N.