Symptoms are that the system responds sluggishly when engine rpms are low, and when switching off there is a gradually diminishing whooshing sound lasting 15 - 20 seconds. The sound is from the area around the cold air centre vent.

Before I start dismantling anything, does the air blend box have to come out to access the centre flap servo?

 

Do you have a Handpump Vacuum gauge? Remove dash cap for access to Center vent flap. Green hose. Attach to hose and start engine. You should see engine vacuum. When you turn off the engine, Do you hear the same woosh? The gauge should diminish. Hook up the hand pump to the Dash pot, pump it up, Do you hear that same woosh?

Larry Louton

 

Thanks removed the crash pad and searched for the sound with a rubber hose acting as a stethoscope. The sound originates from an area between ac/heater box and bulkhead. Only thing I know to be there is the hoses an T-piece in connection with the ventilation fan flaps. The problem had to be in an inaccessible place. Next is to inspect with a boroscope.

Currently away from home so tool access is very limited.

 

Do you have friend that still smokes cigarettes? Remove panel from under steering wheel. The blower motor housing has a blue vacuum line going to it. Remove blue line and have your friend blow smoke into it. The smoke will find the leak. I bet that the leak is behind the radio. You will never see it with a boroscope.

Larry Louton

 

I can always buy myself a cigar 😀

 

Or smoke some weed. But you could also buy a cheap smoke test machine via Amazon

 

So what did you find behind your radio?

Larry Louton

 

weed is better than cigar tobacco. Healthier too.

 

Thing is you don't inhale cigar smoke

Ok, there are no leaks behind the radio. Still haven't had time for a cigar, but hissing sound definitely from between unit and bulkhead. So a cigar is on my purchase list.

 

if this is a USA car, there is a check valve between two rubber lines hanging near or by the battery by the firewall. .

this check valve feeds the a/c Servo. If it gets stuck with debris, it interferes with the Servo operation.

Memorize the orientation of the check valve, it normally has an arrow pointing to interior of car, remove it and blow on it. Air should come out from one side only. If no air comes out from either side, or if air comes out from both sides, check valve is bad.

one possible remedy to free the ball inside the valve is to put it in warm water a while until any debris is loosened by blowing into it. Or just replace it.

 

Good point, will check it.