I got my AC fixed yesterday, blows nice and cold!! The issue is this, when sitting at idle the air is directed correctly where the HVAC **** is selected. But, when i accelerate it shuts off as if it is loosing vacuum. I replaced vacuum lines and capped off the one to the transfer case switch since i am using a cable to actuate the font end. Any ideas? Thanks guys!


Here is a picture since we all love a sexy Blazer! !

 

Vacuum leak or a bad vacuum check valve.

 

Captain Hook, thanks for your response. Where is the Vacuum check valve located?

Your help is appreciated.

 

OK, i found and replaced the check valve...still no change. It is actually worse now. I replaced the HVAC controls this past winter to fix a heat issue. Could that be it? I do here a slight hissing noise from behind the HVAC control panel on the dash. Maybe the one i replaced it with is bad to?

 

Captain Hook, i found this thread https://blazerforum.com/forum/2nd-ge...uestion-89161/
i think it has answered my questions...I'll get a vac pump and start testing to find the leak. I have a feeling it is in the selector switch...

 

Depending on where the leak is, it can sound like the leak is in the mode switch.
This diagram shows which ports should have vacuum, and which ones should not, in each position of the mode switch:

 

After looking at it tonoght I found these things.. mode selector switch is definitely where the hissing sound is coming from but only when it's switched to max AC or norm ac..not on any other settings.. also, I only lose vacuum while driving, I can Rev up the engine while sitting still and ac stays working correctly.

 

Single common denominator for what you describe is: Check the vacuum line, and the recirculating door diaphragm above the passengers feet for a leak. Apply vacuum with the vacuum pump to the orange line, (not the mode switch) at the rear of the mode switch, (port #5) it must hold vacuum indefinitely.

 

I'll be on vacation for the next week so i won't have a chance to work on it until i get back.. I appreciate the help Captain Hook, i'll test the things you have said and see what i come up with. Thanks!