Hissing coming from HVAC head


Oct 1, 2021
On my 81 Malibu there is a hissing noise coming from the HVAC head unit. It goes away if I tap on it. Sometimes it’ll change the air flow to where I select and sometimes I have to direct it a few times. Is it that vacuum switch?? Or any other advice is appreciated!!! Thanks!!!


Living in the Past
Jul 19, 2009
Permanent Temporary
Vacuum leak. Engine vacuum drives the flappers in the ductwork. Pull the radio plate and look for cracked hoses or head unit nipples. Be gentle. The lighter plug comes off by pinching the plug on both sides.

GBodyForum is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. Amazon, the Amazon logo, AmazonSupply, and the AmazonSupply logo are trademarks of Amazon.com, Inc. or its affiliates.

Please support GBodyForum Sponsors

Classic Truck Consoles Dixie Restoration Depot UMI Performance

Contact [email protected] for info on becoming a sponsor