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Strange AC buzzing/grinding issue

2004 - 2008 F-150

Strange AC buzzing/grinding issue

  #1  
Old 05-16-2018, 07:00 PM
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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
 
  #2  
Old 05-16-2018, 11:30 PM
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Incorrect charge? Faulty low or high pressure cutoff switch? Failing compressor?
 
  #3  
Old 05-17-2018, 12:29 AM
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45psi seems to be within range. Measured it with the AC on full blast
 
  #4  
Old 05-17-2018, 07:43 AM
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A low-side pressure reading is only half of what is needed. We need readings from both sides.
 


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