Strange AC buzzing/grinding issue - F150online Forums

Go Back  F150online Forums > F-Series Trucks > 2004 - 2008 F-150
Strange AC buzzing/grinding issue >

Strange AC buzzing/grinding issue

2004 - 2008 F-150

Strange AC buzzing/grinding issue

Old 05-16-2018, 08:00 PM
Vertigo RT's Avatar
Thread Starter
Join Date: Apr 2018
Posts: 10
Strange AC buzzing/grinding issue

Hey, all!
as the temperatures here in florida continue to clime, as they do... Ive noticed a stange issue with my air conditioning.
It started off simply NOT cooling at idle, the air wouldnt be HOT, but ambient at best... I read a little and someone mentioned the clutch fan is inefficient and to install a pair of Mk VIII efans.
Ordered these and while waiting, decided to just do some checks on everything else. With a gauge on the low side piping Im getting about 45psi from the ac line. Seems nominal. The compressor appears to be engaging wheb the AC or “auto” button is used on the HVAC controls. Again though, NO cool air at idle, though it cools nicely while moving.
I did notice though, while in park, if you bring the RPMs up to ANYTHING beyond idle (such as 1200rpm) the compressor will spin and buzz LOUDLY (like a gameshow buzzer) for about a second and then disengage. This occurs about once every 3 seconds, continuously, on and off with the buzzing occuring whenever the compressor engages, and almost immediatly shutting off. My condensor and evap are both new. All else seems factory.
Any thoughts here? Is it an air gap thing? Theres no pings or other sounds at all... just that nasty sounding buzz, almost a grind sound.
Thank you!

2008 Lincoln Mk LT
Old 05-17-2018, 12:30 AM
glc's Avatar
glc is online now
Senior Member
Join Date: Dec 2006
Location: Joplin MO
Posts: 37,858
Incorrect charge? Faulty low or high pressure cutoff switch? Failing compressor?
Old 05-17-2018, 01:29 AM
Vertigo RT's Avatar
Thread Starter
Join Date: Apr 2018
Posts: 10
45psi seems to be within range. Measured it with the AC on full blast
Old 05-17-2018, 08:43 AM
Senior Member
Join Date: Oct 2002
Location: St. Louis (Out in the woods)
Posts: 6,556
A low-side pressure reading is only half of what is needed. We need readings from both sides.

Thread Tools
Search this Thread
Quick Reply: Strange AC buzzing/grinding issue


Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2018 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites.
  • Ask a Question
    Get answers from community experts
Question Title:
Your question will be posted in: