When I bought my 74 the seller informed me that the AC compressor was bad and that it was disconnected due to a bad clutch or another problem. So I ordered a new rebuilt AC compressor with the car.
Due to all the other projects I never managed to get the AC back in fully working order until now.
Unfortunately the rebuilt AC compressor came with the clutch coil terminals in the wrong position. They are available with the terminals at the correct 10 o clock position or the 2 o clock position, which is correct for other years.
If the terminals are in the wrong position you cant connect the original wires to them as they are too short. With the high shipping costs it was no option to send the incorrect compressor back.

As it turned out the cars original compressor had a bad bearing and that was the reason why it was disconnected.

My friends Lucky and Steve were here to help me with the compressor project and so I took both of my compressors to Lucky´s workshop, as he has all the necessary tools and experience with these compressors from his own cars.
Originally I just wanted to turn the clutch coil on the rebuilt compressor into the correct position, but then we decided to rebuild the original compressor instead, because it still has the original decal, which is not available as a correct reproduction. All the available compressor reproduction decals are TOTALLY incorrect for the 1974 Cadillacs. The 1974 reproduction decals all show the wrong amount of refrigerant! They are also different in many other details. The closest match of reproductions for 1974 are the ones from 1972 Cadillacs…

We still disassembled the rebuilt compressor to "borrow" its pulley bearing to replace the bad one on the original compressor.
The procedure to be able to replace the bearing and to turn the clutch coil is not too difficult - but you need some special tools. Without those you cant do it. You´ll need a basic clutch puller / installer set for this job and some long nose snap ring pliers to get the retaining rings out.
First remove the shaft nut and the snap ring ( the rebuilt compressors always seem to come without this snap ring) and then pull the clutch with the special puller. Pull off the pulley and take the bearing out and replace it with a new one.
To be able to turn the clutch coil you´ll have to remove another snap ring. This snap ring was the biggest challenge for us. The shop manual lists a special tool for this which we of course did not have… It could be done with a very long nose plier as well, but we did not have these either. So it took us quite a long time to get it out with screwdrivers and self made hooks… You can then simply turn the coil into the correct position.
Putting it back together is pretty straightforward as well, but again you need a special installer tool to get the clutch back on and to adjust it properly.

I will now have to buy a new bearing so that I can put the rebuilt compressor back together and have it as a spare.
I have attached some pics from the shop manual which show how to remove the various parts of the compressor to remove the pulley and the clutch coil.

As always you can find ALL the pictures in my restoration gallery!

You need some special tools to disassemble the A6 AC compressor.
On the 74´s original AC compressor clutch the bearing was bad.
The compressor clutch removed. You can see the bad bearing inside which is normally sealed. Some balls were already missing.
The clutch with some remains of the bearings.
The clutch and pulley removed on the original compressor.
My friends Steve and Lucky at work. We also replaced all the O - rings.
Removing the pulley
Removing the pulley from the rebuilt compressor.
There is this one snap ring we just did not have the right tool for. The shop manual lists a special plier for this. After a lot of fiddling we got it out eventually…
The magnetic coils on the rebuilt and the original compressor
Lucky in action
Once the snap ring is out you can turn the coils terminals to the 11o´clock position or the 1 o clock position. On the 74 it has to be at the 10 o clock position, otherwise the connecting wires are too short.
Getting this snap ring out was the hardest part on this job, due to not having the right tool for it.
The terminal at the incorrect position at the rebuilt compressor.
We turned the terminal to the correct position.
We sandblasted the pulley while it was out of the car so that I can repaint it now. Note the original decal! All the available reproduction decals are totally incorrect for the 1974 Cadillacs. The reproduction decals all show the wrong amount of refrigerant! They are also different in many other details. The closest match of reproduction decals for 1974 are the ones from 1972 Cadillacs…




The air condition of my Cadillacs always surprise in a negative way. Every spring something new does not work after I wake them up from their winter hibernation.
This time the 67 Eldorado had a new problem which I had to fix.

It suddenly only blew hot air out of the AC outlets. It did not change modes at all. That was a sign of a weak vacuum signal…

I started to inspect all the AC related vacuum lines of the car which checked out fine. Next I did the test I´m describing here in an older posting, as I suspected that the power servo had a problem.
I soon found out that still not enough vacuum was supplied through the transducer.

That meant that either the transducer could be faulty, the temperature sensor could be defective, or the dash control head would not work properly. I took out the temperature sensor of my 67 Deville to test it in the Eldorado but it did not change anything.

I then removed the control head and tested it with a spare one I once bought cheaply on ebay. It did miss some connectors and switches, it had some blemishes on the chrome and did not look good enough to install it into any of my cars. When I put it into the Eldorado anyway the AC suddenly worked perfectly again.
So I removed all the electrical parts from this working unit and transferred it to the perfectly looking but defective control head. After I had swapped all the usable parts I put the unit back into the car and I now have a perfectly working unit once again.
It looks like that there was a problem in the amplifier part which translates the signal coming from the rheostat into a current going to the transducer which regulates the vacuum going to the control head and the power servo.
Lets see what issue comes up next spring…

The Rheostat when set to the lowest temperature setting shows around 2,5 Ω You can check if it is working with an Ohmmeter.edge
At the highest temperature setting the resistance is getting lower.edge
The Amplifier part of the control head is on the underside. Something in here must have gone bad on my control head. I will try to find out what went bad and repair it to have a spare part.
The 67 Eldorado is back on the road for the 2015 season.


The 67 Eldorados new POA valve and recharge of the AC

The Eldorado leaked all of its refrigerant charge over the winter, so it was time to bring it back to the shop. It was recharged with R134 and all the necessary changes were made for the conversion.
I got a new remanufactured POA valve (suction throttling valve) from Classic Auto Air to make sure that the system can cope with the much higher pressures of R134. Classic Auto Air was very helpful with providing the factory correct parts. Classic Auto Air says that the re-calibrated valve can make a 15-20º F / 6º C difference.
Yesterday I got the Eldo back from the shop and so far it seems to cool the car down properly. The air discharged out of the vents is 10º C / 50º F cold - not bad for R134.

This is what Classic Auto Air is recommending for a change from R12 to R134:

Minimum Requirements

  • Change or restore the filter-drier.
  • Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
  • Insure that the system is clean and free of contaminants (Depending on component condition, this may be a simple matter of blowing out with compressed air or liquid flushing with an air-conditioning flushing agent)
  • Replace or restore all rubber hoses with barrier hose.
  • Install 134a charge port adapters
  • Send POA valve in to be calibrated
  • Charge with 134a between 70-80% of the original R12 charge amount.
  • Replace any o-rings with 134a compatible


  • Install hi/lo pressure switch


  • Ignore the sight-glass. A properly charged 134a system will likely show bubbles in the sight-glass.
  • Typical 134a charge rate will be approximately 70-80% of the factory R12 charge amount.

The new factory correct POA valve. Internally it was calibrated for the use of R134 instead of R12. The expansion valve was also replaced together with the evaporator, condenser, compressor, O-rings, filter-dryer. I did not install a hi/lo pressure switch which would cycle the compressor on and off to keep the car original.


The 1967 Cadillac Automatic Climate Control system - more issues - and a final fix. Restoring the power servo valve!

When I took my 1967 Eldorado and my Deville out of winter storage and tried everything, I ran into some problems with the Automatic Climate Control once again. (see this post with vacuum diagrams and also this posting about my blower issue and this post)
The 67 Eldorado lost its complete charge of refrigerant over the winter - so it will have to go back to the shop to see where it is leaking. All components were replaced with new ones last year and so I have no idea where it could have leaked out. A tracer was put in before the last recharge so we should be able to find the leak. I guess that it will be one of the original hoses are a bad fitting.

Another thing that bothered me was that the system basically worked most of the time, but sometimes I had to wait for a long time before the system came on, or I had to switch to “FOG“ or “ICE“ position before the blower would come on in the “Auto“ position. Then sometimes the blower would cut out again if the temperature dial was moved to a colder temperature. Sometimes the temperature would move to full heat regardless off the selected temperature in the 67 Eldorado.
I had the very same problems on my 67 Deville as well - but there also the “Vent“ and “Low“ position did not work at all...

So I started trying to find the issues and finally wanted to fix them. Sounded easy - but it took me 4 full days with long nights in the garage to fix it...
BTW - Cadillactim has an excellent trouble shooting guide for the ACC on his website - its for sale for $ 45.- and I can highly recommend it if you are troubleshooting your 1967 or 1968 Air Condition System.
The best troubleshooting guide for 1967 and 1968 Cadillac´s Automatic Climate Control Systems I got from Gary Sisk - owner of a 1968 Cadillac.
This is a very easy to follow explanation which will save you a lot of time and you do not even need any special tools.
It was written by Lynn Nicholls and can be found on Stampies Cadillac page - here is the direct link to it. I used some excerpts from his document in the explanation below:

I first suspected a vacuum leak to be responsible for most of the erratic behavior of the system. A clear indication was that the system would initially have to be switched to the “ICE“ position to make the blower come on.

Lynn Nicholls writes:

“Sometimes the dash control can be switched to the fog or ice positions to bring the blower motor on and then when it is switched back to auto the blower may stay on and the system seems to work fine until the car is shut off. If the vacuum leak is only moderate there may be enough vacuum to hold the master switch closed once it gets , but not enough to pull it closed in the first place. When the dash control is switched to fog or ice, it assumes the air temperature is cold and that the engine is not yet warmed up, but that the blower is needed immediately for defrosting the windshield. So it supplies vacuum to the master switch through another circuit, bypassing the temperature controlled vacuum switch on the heater core shutoff valve on the right fender well. This source of vacuum is enough to close the master switch.When the dash control is switched back to auto this vacuum source is shut off, but there may be just enough vacuum left from other circuits to hold the switch closed. This routine will work for a while but as the leak gets worse, there won’t be enough vacuum left to hold the master switch closed anymore and the blower will shut off again as soon as the system is switched back to auto.With these symptoms and behavior the problem is most likely the power servo. This is half the brains of the system; the other half is the control panel in the dash. The power servo is controlled by a varying vacuum signal from the transducer. This vacuum supply is a completely separate circuit from that which supplies vacuum to the master switch. High vacuum moves the servo to the maximum heater position, and with low vacuum, a return spring moves it to the maximum AC position. In between these two extremes, it regulates the air temperature door to blend warm air and cool air, and simultaneously regulates the blower speed. It also spins an internal rotary vacuum valve back and forth that makes various connections between the several small vacuum lines on the top. This rotary valve controls the various vacuum motors of the system that operate the AC, heater, and defrost functions. It is this rotary valve that goes bad. l have seen these things visibly warped, and very badly so. It must be caused by engine heat, because there is also one inside the car on the control panel that is moved back and forth by the dash control lever, but that one seldom seems to cause any trouble. A warped rotary valve leaks all kinds of vacuum and the first part of the system to be affected by low vacuum is the master switch; there’s not enough vacuum there to close it and turn on the blower. To verify this is the problem, take some spare vacuum line, some scraps of 1/8 inch pressure line (like for air shocks), and a vacuum T and manually make the connections that the rotary valve should make in the maximum AC position. The connections that the rotary valve makes in various positions are shown in the factory shop manual. Disconnect the black connector with the striped vacuum lines from the power servo. Connect the yellow, red, and purple lines together with a T; also connect the tan and blue lines together and connect the orange and green lines together. If this rotary valve is the one and only culprit the AC will now work beautifully and the blower motor will come on every time, like magic. With the dash control on high the system should be recirculating air and there will be a lot of air noise coming from under the right side of the dash; when the dash control is moved to auto the air door should move to provide fresh air and the system will become much quieter. Of course with these manual connections the system is not fully automatic and the heater won’t work right at all, however this is enough to diagnose the problem.“

I did this test (see picture below) - and with the power servo bypassed everything worked as it should. This way I knew that the power servo was to blame for some of my problems.

So this rotary valve needed to be repaired...
I removed it from the power servo and disassembled everything.

The removed power servo

after opening the cover, you can see the rotary valve in the lower center.

remove one screw and a clip and the rotary valve comes out.

The rotary valve consists of two halves which make the connections - as you can see it was very dirty and rough - and slightly warped.

I started to wet sand both halves with 800 grit sandpaper.

When everything was flat and shiny again I used some 2000 grit sandpaper for a perfect finish.

Looks shiny and flat again

Make sure that none of the ports are clogged - I used compressed air to clean everything.

When you put the two halves together lubricate with WD40 to make sure that when you put them back into the power servo that they are properly held together with the underlying spring.
After I reinstalled them into my cars - almost everything worked as it should. In the 67 Eldorado I still had the problem that in the “AUTO“ position the fan would always be slow - so I knew that the control head in the dash had a problem with the “LOW - AUTO“ switch as well.
In the 67 DeVille the “VENT“ and “LOW“ position still did not work at all...
So I switched the control panels between the two cars and suddenly everything in the 67 Eldorado worked perfectly. I never had such a perfectly working system before. Its like it just left the factory!
In the DeVille I still had no “VENT“ and “LOW“ settings working... So out came the control panels again... (its a pain in the a*** to remove and install them...)
As it turned out the “LOW-AUTO“ switch on one panel was stuck in the “LOW“ position. You can easily remove it and readjust it to work again - sorry I forgot to take pictures. Make sure that all switches on the control head are adjusted properly or they wont work as they should!
So I knew that both control heads were working correctly by installing it back to the 67 Eldorado and the other panel back to the 67 DeVille.

While the 67 Eldorado was perfectly fixed now with everything working as it should - the 67 DeVille was still giving me the problem with a non working “VENT“ position...
I studied the shop manual for hours and could not find what the problem could be. I knew that the power servo was working perfectly now and I knew that the control head was in perfectly working order as well. I verified this once again by switching these parts between the cars once again and everything worked as it should in the Eldorado but not in the DeVille.. I´m really good in switching these parts between my cars now ;-)

I started to look for electric connection problems and finally found out that no electricity was coming out of one of the three power servo connectors, but I did not know why...
After I removed the power servo once again to re-check it again it struck me - one of the pins was slightly bent and the wire connector did not make proper contact. This problem was not visible with the power servo installed in the car. It took me 2 long nights to find this little flaw... I just bent it straight and everything works as it should on both of my 67 Cadillacs. Now I have to recharge the systems and I should have perfectly working AC again... I will also install new dryers and a re-calibrated R134 POA valve before the recharge.
One the one hand the 1967 ACC is very complicated but once you know how it works its pretty easy to fix. The rotary valve in the power servo is pretty easy to refurbish, the dash servo valve is riveted together unfortunately, so its not such an easy fix, but NOS valves are still available at “Classic Auto Air“

Here is a video about the Master Switch that a gentleman posted on youtube

The 67 Eldorado in front of the garage after the AC system was fixed.


The 67 Eldorado is at the restoration shop again

Yesterday the 67 Eldorado was picked up by the restoration shop. As some bolts broke off when I tried to repair my waterpump issue, and I do not have the necessary tools and skills to deal with broken bolts, he came by and picked the car up. He and his team will fix that for me hopefully soon.
Also on the „to do list“ is to install a new condenser for the air condition, recharge it with good old R12 and to fix a problem with the ignition timing. Cant wait to have the car back!

As I could not start the car we had to winch it up onto the trailer
Its pretty heavy...
Almost up...
Good bye!


The 67 Eldorado´s Automatic Climate Control System is back in working order

Today I managed to solve the issue with the partly non working Automatic Climate Control of my 1967 Eldorado. As described in the entries below, the blower would only come on in full heat modes when the car was accelerating. The AC of the Eldorado is very similar to the one from the DeVille btw.
I suspected a vacuum leak somewhere in the system. Troubleshooting began with going through all the vacuum hoses. I replaced some which were a little worn out at the connectors. I also cut off the ends of most hoses, as they were all becoming a little loose during the last 40 years. I then plugged them in again.
Not much did change though.
When I came to the hose of the hot water valve and the delay relay, I had the first success. At least the blower motor would stay on in all “Auto” modes, even when the car was idling - but would still go off in “Fog” and “Ice”. I then suspected a leak in the power servo or in the dash controller. So I installed the power servo from my 67 DeVille where everything works perfectly, to be able to rule out any problems. Nothing changed though - the blower would still come on and off depending on the throttle position.

I then soon found the culprit of the whole issue - it was the master vacuum switch - which seems to have a problem with the internal electric switch. As I had a spare one around I installed it - and voilá - everything worked as it should. It always looked good when I checked it before.
I´m very happy that everything is back in working order. The only thing which I still have to repair is the fast idle diaphragm which completely dried out and is no longer functioning. Fortunately I do have a spare 429 engine in the garage from where I can grab and use this part - so I will repair it soon.
I then need a new condenser which is already on the way across the Atlantic coming from Old Auto Air.
By the way - Cadillactim has an excellent trouble shooting guide for the ACC on his website.

The evaporator had to be replaced as well along with the heater core. This is a pretty big task as you can see on the pictures below. You even have to remove the hood to get access to the whole unit. The fiberglass AC enclosure had to be repaired at my car as well as the previous owner tried to repair the evaporator and missed a screw and made a tear into the enclosure. The restoration shop repaired this professionally and it looks like new now.

The best troubleshooting guide for 1967 and 1968 Cadillac´s Automatic Climate Control Systems I got today from Gary Sisk - owner of a 1968 Cadillac.
This is a very easy to follow explanation which will save you a lot of time and you do not even need any special tools.
It was written by Lynn Nicholls and can be found on Stampies Cadillac page - here is the direct link to it.

Below you can find some pictures of my system:

The whole AC unit has to be removed to get access to the evaporator and heater core... The slight surface rust that showed up where the gaskets were, was removed as well of course...
The big hole on the left is where the blower motor is installed.

This is where the AC box usually is installed

You can see how much has be removed just to get to the evaporator and heater core...

I discovered the first issue at the hot water valve
The hoses around the time relay delay were leaking a little bit
For testing purposes I hung a spare master vacuum switch into the car - this solved the problem
The old fast idle diaphragm was leaking and brittle and was replaced with a better one...
1967 Cadillac Automatic Climate Control Vacuum diagram
The 1967 Cadillac Automatic Climate Control Vacuum Schematic from the shop manual -
1968 is almost identical BTW... Click on the image for a larger view!

Here is a video about the Master Switch that a gentleman posted on youtube