Hum in park, drive etc.,stops with A/C on

[sman83]

Getting a hum from the engine compartment, its intermittent, doesnt matter if its in park, neutral or drive.

I turn on the A/C and it magically stopped. I read some posts through the search and someone mentioned a A/C clutch issue and not a transmission problem.

Trying to get an idea if it is the A/C clutch vs. the trans *praying*

It is the original A/C compressor, clutch and its never needed a recharge.

Thank you mucho!

EDIT:

I ran some diagnostics on the Mounty with ScanXL and it indicated a A/C high pressure, whether that makes a difference, I couldnt say

 

[deweyville65]

Pretty hard to diagnose with that little information, but, possibly the a/c clutch or may be the idle air control. Take a length of hose, hold one end to your ear, and probe the likely areas with the other end.

 

[sman83]

The IAC is relatively new, just replaced it last year, but Ill try the hose and see what I come up with.

 

[koda2000]

i had an rattle on my '00 Mountaineer whenever the a/c clutch was disengaged. not a hum. it turned out the a/c clutch was badly worn and missing the insulators on the 3 posts between the clutch and the pulley hub. i got a replacement clutch assembly (different design) from Advance Auto Parts for around $80 using a promo code and free shipping. replacing it wasn't very hard. the different style clutch clicks when it engages, but i prefer the "old school" design as there's less to go wrong. the OE design clutches are also available for slightly more money. if it turns out this is your problem, i can give you some tips on changing the clutch assembly that will save you some time.

 

[sman83]

I have to do the brakes on the GF's Grand Famnit first today then ill check out that clutch. The clutch does have 188,000 miles on it. I've replaced the lower and upper idler pulleys, so a bad A/C clutch wouldn't surprise me. I had the center bolt on it fall out on me a couple years back.

 

[Turdle]

The hum is indeed from the iac. With the engine running, unplug it and see if the noise stops. You will then have a check engine light to clear, but this will show the sound source real quickly. Just disconnect the battery while you clean the IAC and the code will be cleared.


The noise seems to be from the internal plunger seal in the IAC -acting like a reed in a clarinet.Cleaning the plunger real good and replacing the air filter should make it go away.