Have a whistling sound - related to AC


Original poster
Jun 17, 2012
Hey all,

I think I'm having an A/C issue - and I'm just trying to figure out where the issue may be.

I have a whistling sound that happens at idle and usually at low speeds. It doesn't happen to often but I usually here it after a cold start. The sound will go away if you turn off the AC. Also, if the whistling is happening when you kill the engine it will last for about 2-3 seconds.

It SOUNDS like it is coming from the AC Evaporator under the hood.

I do notice when this is happening that the AC Compressor is kicking on and off maybe every seven seconds. The air coming out isn't super cold at this point. Once I start rolling - after maybe 10-15 seconds the whistling will stop and the air is ice cold.

It only happens once in a while and when I'm driving the air is always very cold.

Just curious what it may be.. It doesn't sound like it is coming from the belt area or that it is one of the pullies. I don't think it is a water pump or alternator because the sound isn't coming from there.

I did a recent clean of the TB, replaced plugs & fuel filter, also a fresh oil change. When the whistling isn't happening it runs great and idles great even with the AC on. When the whistling does happen it seems like when the compressor engages it tugs on the RPMs a little and gives a bit of a rough idle.

Thanks for the help!


Lifetime VIP Donor
Nov 19, 2011
Portland, OR
Very odd, especially if you have a clean throttle body. Your compressor may be deteriorating, or there's cloggage in the tubing. A pressure test by an AC specialist may be illuminating. I don't recall anything similar being reported in my 7 years on the forums.


Original poster
Jun 17, 2012
Thanks for the reply! I may be mis-diagnosing the issue.. I'll take it in and see what they say. The sound may be coming from something else. A/C reapir is quite a bit over my head anyways. I have nearly 200k miles so the gremlins may just be getting closer to eating the whole truck up.


Jun 17, 2012
The other day I had a 01 Cav stop by with the same issue, The a/c would kick on and run fine the first minute then cycle on and off every 5 seconds dragging the RPM's down when it would engage. I am chalking it up to a clogged orifice on that one, most likely caused by a failing compressor. The compressor is rough when your turn the clutch my hand. Any shavings or dust (junk) that comes out of the compressor when it starts to fail will clog up the small screen in the orifice tube and once the pressure builds up behind it the system was over pressuring and dragging the engine down until the pressure sensor cuts out the compressor, then the pressure drops, the sensor sees this and cuts the compressor back on, rinse and repeat....

With 200k I would say shes seen better days...

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