A/C Vacuum leak

[Les W.]

Hi,

Has anyone detected a vacuum leak from there four seasons A/C? After detecting all other vacuum leaks, the A/C vacuum supply is leaking. Is there any one check that should be the one area to look at before getting behind the dash? 72 LT-1 w/ac Thanks

[Paul Y.]

Re: A/C Vacuum leak

Create a vacuum pump either with a small purchased pump or by running a hose to another auto that is running outside with the door closed. When it is quiet you should be able to hear the leak make a hissing sound and proceed to disassemble at that point.

[Edward J.]

Re: A/C Vacuum leak

Les I had a situation with my 72, There is a vacuum hose under the wiper door pass side that was off, The hose had been broken and laying there for years. this door shuts the outside air off. and recycles the inside air when max a/c is selected.It is in a tough spot. May need a good light. Ed

[Les W.]

Re: A/C Vacuum leak

Ed, I see the green hose that you point out that is under the wiper door. Every thing looks good from where it comes out of the dash area then into the under wiper door area and down to as far as I can see it. In the 72' service manual on page 1A-65 it shows another green hose going to the air inlet valve, which I believe is located in the passenger side kick panel. But the hose color is either red or tan from what I can see. When the vacuum runs out I can hear the spring loaded door close. I will look in the future to see it close. I am sure that the leak is located in the A/C vacuum system. When the supply line to the system is blocked the vacuum holds well in the rest of the car. It looks very complicated to possibly find the leak. I just don't know where to start.

[Edward J.]

Re: A/C Vacuum leak

Les, Does everything appear to operate correctly when you use the thumb wheel for the modes? I have a the situation with my 72 after about 45 seconds I hear the same thing(spring of one of the doors closing) with my 72 A/C car. I just think its something with the wiper door or the recycle door under the wiper door.from what I under stand form the point of the vacuum system it should only have to hold a vacuum for about 30 seconds after the key is shut off. My car has no operation problems with any of the vacuum functions.

[Les W.]

Re: A/C Vacuum leak

Ed, the best I can tell all the four seasons A/C functions opperate the way they were intended. I will review them again to make sure. With respect to the other vacuum systems, the headlights and the wiper door units work and hold vacuum. Initially they were a problem but they function well now. If you are concerned about your wiper door functions and you have a vauum hand pump, pull the red hose off the wiper door actuator and hook the pump to the actuator to see if that holds vacuum, it should. Then do the same with the green or opening end of the actuator, it should hold vacuum. I used Dr Rebuilds trouble shooting diagram and his sheet explaining the various testings for actuators and actuator relays. The relays can be the major problem as I have found out. For the PV test the headlights must be able to close 60 seconds after egine turn off.

[Edward J.]

Re: A/C Vacuum leak

Les everything with the wiper and headlamp function with no issues on my car. What I was thinking was that the vaccum systems were meet to hold a vacuum for only a short time after shuting the engine down. I remember someone posting during a PV that its like about 30/45 seconds. after shut down that you still should be able to open the headlight buckets with the vacuum reserve in the tank.

[Les W.]

Re: A/C Vacuum leak

Ed, the PV manual requires the 30 second test to pass. When I first tested it would go to about 45 sec. at max. Now it holds for 6 to8 minutes. They say a tight system should last for 30 minutes. What I did to test the system is to 'T' in a vacuum gauge to a line that is holding and supplying vacuum. Then when the car is turned off start a stop watch. When I blocked the A/C supply the time was around 15 minutes. The system overall is good but I was hoping I could find someone who may have ventured into repairing the A/C vacuum system, and may be able to shed some light on where to look like you did. Thanks, Les

[Terry M.]

Re: A/C Vacuum leak

Hi,

Has anyone detected a vacuum leak from there four seasons A/C? After detecting all other vacuum leaks, the A/C vacuum supply is leaking. Is there any one check that should be the one area to look at before getting behind the dash? 72 LT-1 w/ac Thanks

One place to check before getting under the dash is the rotating control wheel in the HVAC console -- not the temp control wheel. That system control wheel has holes in it to shuttle the vacuum from one port to another. There are no seals on those holes. As the shaft loosens with use vacuum will leak betweent he wheel and the housing.

You may be missing a major leak under the dash by not properly troubleshooting the entire system, but if you want to shootgun the issue (and I don't recommend that) try the control wheel.

[Les W.]

Re: A/C Vacuum leak

Hi Terry, I will look into the control wheel by trying to listen for a leak, if that is the way to find out? When you mentioned 'not properly troubleshooting the entire system' are you refering to the A/C system or the entire vacuum system in the car? Also, by shootgun the issue, do you mean taking apart the A/C system? Have you or do you know of anyone who has taken apart and repaired the A/C system due to a vacuum leak problem? The leak I am experiencing is minimum and I may just be inclined to leave it alone. One other question for you. I have an LT-1 with A/C and when I engage the A/C at idle it draws down about 3 to 400 RPM's, is this normal? The PV manual says 100. Thanks for your help.

[Terry M.]

Re: A/C Vacuum leak

Hi Terry, I will look into the control wheel by trying to listen for a leak, if that is the way to find out? When you mentioned 'not properly troubleshooting the entire system' are you refering to the A/C system or the entire vacuum system in the car? Also, by shootgun the issue, do you mean taking apart the A/C system? Have you or do you know of anyone who has taken apart and repaired the A/C system due to a vacuum leak problem? The leak I am experiencing is minimum and I may just be inclined to leave it alone. One other question for you. I have an LT-1 with A/C and when I engage the A/C at idle it draws down about 3 to 400 RPM's, is this normal? The PV manual says 100. Thanks for your help.

I meant troubleshooting the HVAC system. From yoru posts you seem to have already isolated what leakage there is to that system.

By shootguning I meant changing/repairing parts without troubleshooting to determine that the "issue" is with that part.

A drop of 3-400 sounds like a lot more than I would expect. If I were doing a PV I could tolerate 150, and maybe even 200, but what you are relating sounds excessive. Be sure your distributor map and settings are correct and the vacuum advance is working properly.

[Edward J.]

Re: A/C Vacuum leak

Les, Also check the RPM drop with a meter or a timing light if it displays RPM . and then check the tach. in car to so if its accurate. I also believe that there is a solenoid on the carb. that bumps up the RPMS when compressor is engaged. once the compressor is on you may have to touch the accelerator pedal to help it to step up the RPM, Because the solenoids sometimes may not have enough to override the return spring on carb.


Sound correct to you Terry?

[Terry M.]

Re: A/C Vacuum leak

Yep, Ed that works for me. I forgot about the solenoid.

[Les W.]

Re: A/C Vacuum leak

I'm not sure there is an idle boost solenoid for my car. On page 1A-77 in the 72' Service Manual the Engine Idle Compensator is in the carb. Could that be the solenoid you mentioned?

[Edward J.]

Re: A/C Vacuum leak

Les, good question because you have the LT1 engine and the holley Carb. does you car maybe use the T.E.C. system, Which is a vacuum controled operation. does your car have vacuum controled plunger on the side of carb. it may pull double duty with a A/C car. this maybe a Terry Question 72 LT1 a/c cars are rare. and maybe different from prev. years.