RTK

Hello everyone I dont know if this question has been brought up or if my cars the first, but anyways, ever since I bought my car a few months ago it has been making a hissing noise from the AC even though its been turned off. Sounds like air leaking out of a baloon slowly. once I turn my Air conditioner on the hissing goes away after like a minute. Is this a common issue or do I have to fix somethin? thanks

Bill Curlee

Sounds like your air diverter door module, a vacuum motor or one of the vacuum lines has a vacuum leak. Your going to meed to disassemble most of the dash to figure out what it is. Here is a picture of the entire HVAC unit removed from the dash.





The FOAM covered tube in the center of the pic is a vacuum vent!







Vacuum lines from vacuum module:







VACUUM MOTORS





DO YOU HAVE ALL YOUR DOOR FUNCTIONS WORKING CORRECTLY?

BC

RTK

YEs all of my door functions work properly. Also my AC smells sort of bad now for some reason. Is that some sort of indication that I need to replace something?

Showdown

My AC will blow from all locations at once, Mostly out of the winshield vent. I hear a hissing comming from behind the motor when I shut the car off. HELP.

LoneStarFRC

Sounds like the vacuum line at rear of intake manifold disconnected. Different problem than RTK's.

LoneStarFRC

Even if your doors are working with the engine running, one of your vacuum motors to one of the doors may be bleeding off vacuum after engine shutdown.
Vacuum reservoir tank also maybe Bill?

Showdown

How hard is it to fix if it is the vacume line behind the manifold? Should I have the dealer look at it?

projectjim

Trace the line down,out of the firewall,and it's probably cracked where it connects to the manifold.Fairly easy fix.

RTK

Is there a DIY or something that explains what tools and parts I will need to fix this problem? thanks everyone

LoneStarFRC

The intake manifold has to be removed (or at least moved forward a few inches) in order to get access the small (1/8" black nylon) vacuum line where it attaches to the manifold.
Try to clarify if the sound you're hearing is coming from the rear of the engine between it and the firewall and not just somewhere in the area. Has the intake manifold ever been removed or changed? If any work has been done of that nature then it's highly likely that's the problem.
On the other hand, if you've ever had a battery leak problem in the past, there's the possibility the acid dripping down may have attacked the line where it exits the firewall (and other items in the area too like the PCM, wire harnesses, etc)
This subject has been discussed a lot here. Good news is, it's not a high $ repair (as far as the line itself).
Try a search.

bighank

Most C5 Delco batteries LEAK ACID onto the hard plastic vacuum line going to the A/C flow control valve. Check this FIRST. Usually need to replace MOST of the hard line coming thru the cables with the wires and the vacuum lines in the middle. Was my problem and causes no control of where the air comes out. BIGHANK