Air Conditioning issue vacuum related?

[Doug Meloan]

It has been way to long since I have been on this website as much of my time this past year has been working on the restoration of my 61' Coupe deville. It sure has been fun taking both of the 61 and 63 Cadillacs to car shows and parking them side by side.  Always a crowd pleaser and fun to hear the comments such as "now that was when a car was a car".  Anyway to get back to the air conditioning vacuum question, which is really a two part question. First question involves both the 61 and 63 cars.  I have noticed that when I accelerate to go up a hill or pass a car, etc..that the airconditioning blowing from the vents will all but disappear. Once the load is released (let off the gas pedal) the air conditioning willl start blowing out again as normal.  Is this just typical, or do I have a vacuum issue with both cars.  I don't remember the 63 doing this before, but maybe just ignored it and didn't think much about it until the 61 did the same thing.  Second part of this questions regards only the 63. I  recently started hearing a hissing sound (air leak) from under the dash but only when in "Park". Once the car is taken out of park the hissing stops and the AC will blow out the vents, put it back in park this hissing starts and the AC quits blowing out the vents. This is hard to explain as it acts different from time to time in different situations, but any ideas of where I should start my search.  Thanks, Doug 

[3ft7bqmb7dryo]

I have been thinking about this idea; If your vacuum valve is bad, get the electrically controlled vacuum valve, 5 pin relay, and a few hours.

The idea is that the brake light switch will control the electric vacuum valve.  The relay will protect the brake light switch from overheating.

Theory of operation;  Set the parking brake when you come home from work. In the morning you start the car. When you put your foot on the brake, the parking brake releases.

[3n49omug8n28i]

Your on to something there Russ. How about wiring it into the reverse on the NSS? Break light switch is always hot so it could be released with stored vacuum?

[3ft7bqmb7dryo]

I thought the brake lights were switches on, but I'll have to double check.

[3n49omug8n28i]

You may be right about the brake lights Russ. But it would be closer to original by only coming off when put in gear. If someone was tuning the car while another person was inside of it and they touched the brake it would pop off. Just a thought, regards Russ. (If anyone will figure it out you can LOL)

[30cg3u76xzb0t]

If I'm not mistaken the brake lights are on a switch connected to the brake pedal
The back up lights are on the NSS (neutral safety switch)

[3n49omug8n28i]

Hey Joe, Russ was thinking of an electric solenoid to switch on vacuum to parking brake and release it. He suggested using the brake light switch as the trigger. I suggested using the reverse light as the trigger as the car would have to be put into gear to release the parking brake. There by making it a bit safer.