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 

[David Thomas]

Hi Doug, welcome back and good show on the 61 & 63! On the 63 and most likely also on the 61, there is a vacuum check valve under the dash on the firewall just above the accelerator pedal. If that valve fails, it will allow the vent actuators to loose vacuum in the system when manifold vacuum falls from hard acceleration or heavy throttle like climbing a hill. Once manifold vacuum returns all goes back to normal. The hissing noise in park is most likely a leak in the neutral safety switch vacuum valve, failed emergency brake release actuator, or a cracked hose in that circuit. You'll have to climb under the dash to check these items. Good luck, hope this helps.

[Doug Meloan]

Hi David,  Thanks for the information. Is the vacuum check valve that round (quarter size) white plastic connector that has three vacuum hose ports on it?  If so one of the things I tried was to remove the vacuum hose from thë neutral safety switch to that white plastic valve and taped the end of the hose off.  Hissing stopped but lost the automatic brake release and did not solve the vacuum vent actuator problem. If it is the vacuum check valve are these available or a nightmare to try and find a good working one? 

  

[David Thomas]

The original is a white/cream color plastic. The manifold vacuum comes in from a hose attached to the wiring feed through gang plug on the firewall. The check valve has connector barbs that supply vacuum to the neutral safety switch and the vacuum control head for the heater and air conditioning. I don't think the original style is available now but I think you can buy a modern version of one from the box parts stores or maybe Jason or Russ has one in their stock. I bought one from a Bumper to Bumper store many years back, it is black and has an extra barb on it, I just capped off the unused port, worked for me. Take the original check valve with you to a Napa etc. to match up the hose barb size.

[Jason Edge]

Hi Doug. The loss of vacuum definitely points to the check valve as David pointed out. I am out of these but believe there are some aftermarket versions.  There is a newsletter article and video on testing these on our Help Page pulled from a previous newsletter. Here are the Help Page links:

Check Valve on Insulator Board - Testing
Article: http://6364cadillac.ning.com/forum/topics/testing-the-check-valve
Video: https://youtu.be/FDyP44bO15U

[3ft7bqmb7dryo]

Doug, I think I'm out too, but this is a part that just gets tired with age.

I made a simple vacuum check valve, with a plastic T, and a simple in line vacuum check valve.

[Doug Meloan]

Thank you Russ.  Looks like I will have to find one at the auto parts store and adapt it.

[Doug Meloan]

Hi Russ, I need to make one of these check valves like in your photo. I noticed on the plastic T fitting that both barbed prongs are the same diameter, however, the vacuum line coming from the ac/heater control  switch is a smaller diameter hose than the one going to the NSS (I am assuming, possibly incorrectly, that is what the two T fitting ends are for). I am confused by your photo so can you help explain how this improvised check valve set up should all go together? I am sure that I am trying to make it more difficult than it needs to be.  Thanks, Doug

[3ft7bqmb7dryo]

Doug, you can get different sized Y fittings and reducers at your fav parts store. The idea is to keep vacuum in the lines inside the car.  Put the check valve in line coming from the electrical box on the fire wall. Then just use a T fitting where the original check valve was.  You can use a reducer where the line gets smaller.

[Doug Meloan]

Thank you, Jason.

[30cg3u76xzb0t]

This what I did today, got the check valve from Advanced Auto & since my Neutral safety valve is not holding Vacuum I capped off the vacuum line going to it. I tried bypassing the E brake completely by running a vacuum line from the Tee that connects the NSS to the E brake put for some reason it would not work,(meaning the Idle speed up controller would not engage)   so leaving it connected & capping the vacuum line going from the Tee check valve to the NSS worked. Meaning the Parking brake is no longer working with Vacuum ( you have to hand release it ) and the AC vacuum system is working the way it should, Idle speed controller coming on when you turn on the AC, fan is working on reg & max, blowing cold out of the vents. Only took 10 years to get it right & just in time for winter LOL 

[30cg3u76xzb0t]

I got the ideal from Russ

[30cg3u76xzb0t]

Worth its weight in gold !