AC noise under throttle

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

texdave

Junior Member
Joined
Mar 28, 2024
Posts
4
Reaction score
2
Location
texas
First Name
tex
Truck Year
1976
Truck Model
C10
Engine Size
350
Truck: 76 GMC C25 Suburban w/454 + 3 speed auto + factory air conditioning

When I'm driving and have the air conditioning on (Max or Normal mode, at any Fan speed) I hear what sounds like a short sucking sound every 40 seconds or so. It gets louder as the RPMs go up and I don't believe I hear it at all when at idle. I don't hear that noise when the A/C is off or when I switch the mode to Vent.

Here's a link to a video I took that shows this in action:
xc_hide_links_from_guests_guests_error_hide_media
.

Is this a vacuum leak on a line that goes to the HVAC controls or something else? Appreciate it if you can point me in the right direction.
 

75gmck25

Full Access Member
Joined
Oct 13, 2016
Posts
2,235
Reaction score
2,154
Location
Northern Virginia
First Name
Bruce
Truck Year
1975
Truck Model
K25 Camper Special TH350 NP203
Engine Size
5.7
The A/C controls run off engine vacuum, and the vacuum reservoir under the hood should keep the controls vacuum relatively constant.

Maybe your vacuum reservoir is not keeping up (leading?) and maintaining vacuum, and the controls cannot hold the vacuum pods in position. This would cause the doors in the HVAC to move back and forth as vacuum rises and falls.
 

Latest posts

Forum statistics

Threads
43,931
Posts
945,939
Members
35,977
Latest member
Sam campbell
Top