I bought this beauty a year ago and at that time the AC system was flat.  I replaced a line that had a huge hole in it, pulled a vacuum, charged it with R12 and it started making cold air !!!! Oh happy days !!!

AC runs great until I take the transmission out of Park (and put it into Drive or Reverse).  At that point it just fan shuts down.  If I put it back in Park the fan starts blowing cold air again. 

What the heck ?   My only thought is that it might have something to do with the neutral safety switch (it hisses when I put car in Drive). 

Any suggestions ??

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Did you reply in invisible ink?

No. Weird. It was a really good reply too that I don't have time to re-type. I'll sum it up by saying find the source of the vacuum leak & it should fix the problem: hoses, NSS, check valve, auto-release for parking brake, etc. All under the dash near the steering column.

I always write my posts in invincible ink...   ;-)

Good looking car
Love the color same as my 64 convert
Not that many 64's around in that color
Sure feels like the NSS is part of the problem With your symtoms
I would examine all wiring to the NSS as a start to see if any wiring looks like it was tampered with in the past ( wiring crossed )

The fact you got it to blow cold air so easily is a blessing
Feels like an electrical issue of coarse

You could always just hang out in the driveway to cool off ---LOL !

Should be real great once you solve the problem
You are very lucky to have the original r-12 that the system was designed for


I do second Kusts suggestion about it being a vacuum issue
The 64's with comfort control have so very many places for vacuum leakes to take place

Examine and test all vacuum lines to see if they are holding a vacuum at all

If you find a leak you can plug the line with a screw so all else works and get back to that issue later

Do check your dist vacuum advance for holding vacuum while checking the other vacuum lines

You can eliminate all the cars internal cabin vacuum issues by closing off the larger vacuum line coming off the back of the intake manifold that goes into the cabin
Is just a bandaid for future system trouble shooting vacuum issues in the cabin
Any vacuum leaks in the cabins comfort control system is going to effect the engines performance producing a vacuum leak in the intake manifold
The vacuum leak is letting unwanted air into the intake manifold having the engine run leaner and hotter than it would run otherwise
The engine is not pulling air through the carb venturies as it should be with a vacuum leak at another location on the intake manifold
Having the engine right has always been my own first thing to get right when getting the car on the road

Closing off the vacuum line from the back of the engine will not help with your present AC issue until all of the CC is checked out
It might even stop the AC from working but the cars engine performance will be closer to what it sould be if the cars engine is properly tuned and on spec

The color of you spark plugs is your best source of knowing the condition of your fuel mixture is in your cylinders
You want your plug tips to be a brown paper bag color when its right

At some point you need to test every vacumm line and a number of vacuum valves in the CC system
At a minimum cut off a 1/4 inch off all vacuum lines and reinstall them

That should keep you busy for a while


What the hell is invincible ink ???


Superman branded invisible ink, making it invincible ink.... geez Tony, don't you know nuffin.

It might be time now to put Roberts thread back on track.


There is a vacuum circuit diagram on either page 13-20 or 13-22 of the 1964 shop manual - if memory serves - I don't have it with me at the moment.  That diagram shows that the vacuum to the NSS and the vacuum to the control head of the Automatic Climate Control inside the car, are interconnected. There may also be a check valve in the line.

Update -  See attached picture.  I found this line disconnected under the dash.  Thanks guys.  Air not blowing real cold so I'm going to check the charge.  I bought the bible on fixing 1964 cadi ac systems last year.  I have to spend some additional time with my nose in that book.

Thanks again.



That's good, troubleshoot first. Then buy parts.

You should be spending in the neighborhood of $800-$1000 dollars in replacement parts if you do the work on the AC yourself to repair it to work ---for the long haul
You will find outstanding info on the search engine and Help pages here regarding the cost of parts and the best place to get them
I assume you have Cadillac Tims book on the subject
Clovis has done a lot of replacement work on the system and has shared his work on this site for everyone to understand
A complicated system with a lot of part to address
Read the temp at the vents if you are questioning how cold your system is getting

If your system was open( hole in the line ) you should always replace the dryer when vacuuming and recharging the system
Many systems will require a new updated compressor and some of the Vacuum valves that keep the system doing what it should be doing




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