Ok so when I get into my car and turn it on my boost/vac gauge reads anywhere from 15 In Hg to about 19 In Hg. This is the correct vaccum pressure at Idle I know this for sure.

However when I turn my A/C on my vaccum pressure goes from that 15-19 In Hg to like 5-10 In Hg. This isn't good.

My question is is Vaccum Pressure related to the A/C in some way?

Thanks

 

Does it stay at that pressure, or is it just when you first turn on the A/C? if it's just when you first turn it on, it's because the IAC valve opening to raise the idle (it does this to compensate for the added load of the A/C compressor) allows a drop in vacuum.

 

No it stays there.

I will check again but I'm pretty sure it stays.

 

Yeah it just stayed there when I turned the A/C on.
So what could be the problem?

 

Hmm... I'm not sure if our vehicles use any vacuum- actuated climate control doors... Most cars do, but a lot of vehicles with automatic climate control don't. If your car does have any vacuum- actuated climate control components, then there's a leak in that system. Check for a thin vacuum hose running to the firewall, and look for leaks. A leak in that will certainly account for that kind of vacuum drop. Do you notice any rough idle or surging idle when the A/C is on?

 

1. When I first turn the car on and then the A/C my vaccum pressure goes from around 17 In Hg to 10 In Hg.

2. After the car has warmed up the vaccum pressure goes back down to 15 In Hg which is acceptable but not the best rather have it back at 17 In Hg to 20 In Hg.

 

There are no vaccum lines connected to the AC system. Why it comes on when the compressor turns on, I'm not sure but I'd check all your vac lines and those rubber elbows.