Turning on A/C makes vacuum drop??

[gmrulz4u]

Today was the first time that I've ever used my A/C since I had my AutoMeter Vacuum Gauge installed. I immediately noticed that my gauge was reading 3-5" hg LESS then it was when I turned if Off!!??

 

Am I correct in assuming that this means I have a vacuum leak somewhere in the system? Or is this normal?

 

I also should let it be known that this does NOT happen when I just use the heat. When I use the heater, the vacuum pretty much stays steady. It's only with the A/C that it's dropping quite a bit.

 

I was thinking that it might just have something to do with the ECM commanding a higher idle when the A/C is ON, and since higher RPMs equals lower Vacuum, I thought that "might" be the case. But I would guess that the commanded RPM by the ECM is the exact same for both the Heat and the A/C...and like I already stated, the Heat makes no difference...

 

Anyone know what's going on here? Is there specific hoses that could be leaking that are used during A/C operation but NOT during Heater operation?

 

THANKS!

[Baddflash]

My idle only changes with A/C running and not with any other settings. But I don't have a vacumm guage so I can't tell you what that does.

[ctx46]

its suppost to drop a bit,b ut if U leave it @ idle long enoughf it will actually come back up, and be higher than @ idle with no load....

if U think about what the car's doing when the ac is turned on....

the ac compressor is a pretty good sized load to the ol motor, so it advances the timign, widens the injector pulce with, and most importatly, give it more air (yur vaccume leak) with the aic motor....

I hope this helped ya out some..

later

joe