[rockdoc]

I am replacing my dash lights with LEDs and while I had the AC ducts out, I figured I'd replace my brittle vacuum hoses under the dash. I pulled out the AC check valve and, for the heck of it, sucked on it from both ends. It seems that it's straight through, i.e., I could suck through it from either end. Everything was working properly before, so I don't know how important it is. But I wondered what it was supposed to do. I figure I'll replace it, as they are available.
Does anyone know how they are supposed to work? Could it be contributing to a vacuum leak?

 

[LATECH]

vacuum check valve.Its supposed to let vacuum through and hold it when vacuum drops on the feed side.It keeps vacuum actuators in there place when the supply line loses vacuum, like at wide open throttle

 

[O52]

what LATECH said, It also maintains vacuum for the A/C controls when accelerating or whenever the engine is under heavy load. If your A/C system changes modes under those conditions, the check valve is probably missing or bad.
A leaking vacuum hose will do the same thing when under load.

 

[rockdoc]

Thanks guys. I figured it was something like that, and I'm sure I shouldn't be able to suck through both ends like it's a straight-through line. I'll play with it again tomorrow to see if I need a new one.

 

[rockdoc]

After doing a bit more studying, and spending some time under the dash, I decided to buy a new check valve. I bought one from Inline Tube's ebay store (MotorCityMuscleCar). The valve "looks" correct, and I installed it exactly as the old one was installed, with the large nipple going to vacuum (5/32" line) and the small nipple going to the 1/8" AC/heat control line (makes sense, right).

It didn't work, and none of the flapper valves operated. After checking the valve, I discovered that it had to be installed backwards (for the way the valve is constructed)--you have to hook the 5/32" vacuum line to the small nipple and hook the smaller 1/8" vacuum line to the AC control to the large nipple. You can suck through the valve from the small end, but the large end is essentially plugged off. I contacted Inline Tube and they told me to contact MotorCity. MotorCity told me "it looks correct". After 3 or 4 emails, I gave up.

It works when installed backwards, but unless you are paying attention to the sound of the flapper valves opening and closing, you might not notice that you have to reverse the valve.