1964 Cadillac AC with a 7 port Vacuum control valve

Is anyone having the same problem I'm having ? In park with AC on no vacuum at the fast idle diaphragm, ( so the fast idle diaphragm is out and bumping up the idle) when I put it in drive I'm getting vacuum there. So in park with the AC on the engine is idling at 900 RPM's put in drive it drops down to 450 600 ish. So when your sitting at a red light it feels like the engine is starving for fuel not to mention it's running hotter than it should.

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Comment by Russ Austin on August 25, 2017 at 7:38am

Joe, I remember that you do not have the correct NSS. You have a 65 or 66 if I remember.  Since the NSS provides vacuum to the rotary valve, I would check there. See if your getting vacuum to the rotary valve when in Drive. If not, just bypass the NSS and plug the vacuum lines together. 

We will look into getting you the right NSS.

Comment by Jason Edge on August 25, 2017 at 7:35am

Joe, The AC is working exactly as it should. The Idle Speed-Up control is only designed to increase RPM when transmission is in Neutral or Park and AC is ON. When you put it in Drive the rpm drops back down to the regular 480 rpm. See note 14.H Page 13-29 in your 1964 Cadillac Shop Manual.  Also see Idle Speed specs for Rochester page 8-42, and Carter page 8-43. It is probably noted elsewhere.

The main adjustments are to have car idle with Idle Speed-Up Off set at 480 rpm and the Idle with the Speed-Up on set to 900-950 rpm. 

Setting car idle is on page 8/37 note 33.a. Idle Speed and Mixture Adjustments. Per instructions, the car needs to be in Drive, with AC ON! That applies vacuum to the idle speed-up control pulling it back and effectively shutting it off allowing you to set the idle. 

Setting the Idle Speed-Up Control set to 900-950 per adjustment specs on page 8-40 Note 33.i. Idle Speed-Up control Adjustment.

So. in terms of the idle speed-up control, the car is working exactly as it should --> On in Park and off in Drive. Here is the note on page 13-29:

Comment by Anders on August 25, 2017 at 6:25am

We all, secretly, call Tony Honey. So don't feel embarrassed. :-)

Comment by Anders on August 25, 2017 at 6:23am

I agree that it doesn't seem right. And when you started this thread I was thinking the same way. Then i remembered how the system operates in my car and that's also what's in the manual. The engine should be able to handle the extra workload when the A/C is running. Even at 480 rpm.

I do think you need to set the idle adjustment on your carburetor. It sounds like its too lean. Best is to check with a Air/Fuel Ratio Indicator. I was actually lucky to get, for free,  a brand new (well he bought it -99 and never used it) Halmeter AF-30. It should fit my purpose even if its not a wide band. So gonna install it next time the car is in air.

Comment by Joe DiIaconi on August 25, 2017 at 5:36am

Sorry Tony I didn't mean to call you Honey, I was speaking in to my phone & it wrote that by mistake LOL

Comment by Joe DiIaconi on August 25, 2017 at 5:31am

Anders in the manual it tells you to pull the vacuum line from the parking brake & attach a vacuum gauge then apply the parking brake, So you can put the car in drive & it will not move. So in park with AC on 900 rpm's at idle with no drag from transmission. Then in drive with the drag from the transmission & compressor 480 RPM's doesn't seem right.

Comment by Anders on August 25, 2017 at 5:06am

My first post with the following text was incorrect. Disregard the following:

"In parking (with A/C on) you should now have 900 rpm, as the fast idle diaphragm is pulled. Ask your assistant to put the gear into drive. See whats happen with the fast idle. It should still be pulled by the vacuum and you should have 900 rpm."

It should state:

In parking and neutral (with A/C on) you should have 900 rpm, as the fast idle diaphragm is not pulled by vacuum. Ask your assistant to put the gear into drive. See whats happen with the fast idle. It should be pulled by the vacuum and you should have 480 rpm.

So when you are waiting at a red light and have the transmission in drive and A/C on you should have 480 rpm. As Tony pointed out higher rpm will make your transmission to start to move the car forward. If then over heating or stalling you need to adjust your carburetor. I would be tempted to replace the carburetor with the FiTech system as that should sort out these type of problems.

Comment by Anders on August 25, 2017 at 4:57am

Hmm, found these two sections in the manual. I believe you should adjust the idle setting on your carburetor. And that should take care of your problem.

Comment by Tony and Ginny 429 on August 24, 2017 at 11:23pm
I understand that the idle up vacuum is not working as it should be at the moment but at an idle the car should not feel like it is starving for gas or be running hot as you stated
A spark plug color check might help to evaluate the fuel mixture in the cylinders to see what's going on
Feels like a lean fuel mixture might be the issue
I would recheck the idle mixture adjustment for the possibility of that being part of the idle feels issue as I indicated
Doing that with an exhaust probe would be the more accurate way to check the fuel mixture


Comment by Joe DiIaconi on August 24, 2017 at 5:39pm
Yes honey there are in the front of the carburetor, there's a whole process on how to do it right in the shop manual which I had read and I have done. I believe my problem is the idle up diaphragm is getting vacuum when it's not supposed to be


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