Air Conditioning on, occasional "whoop" sound?

[blkprj80]

I don't know the history, I bought this machine last June and didn't drive it until winter. I only moved the A/C compressor out of the way and back when I did the engine rebuild.

I did put in one full can of R134, the very last of which just cleared up the bubbles in the sight glass. Air at the center vent is around 44F at low fan speed and all the way cold on the slider.

It has a new belt and idler pulley. I have the belt adjusted snug, but not super tight. I tightened it with 2 more turns on the idler adjuster bolt last night and the noise hasn't changed.

I drive a ways, no problems or noises. Then if I stop a while and restart, I hear a "whoop" or "yorrrp" type noise from somewhere on the RH side (US) after driving a ways. It really sounds like it's coming from under the dash, but I can't imagine from what.

Is this noise an indication of impending A/C compressor clutch death?

Is the belt just too loose?

Any ideas?

Thanks fellas!

 

[Coolstream]

I don't think it's the belt. I've heard a noise like you're describing on a few different vehicles. Can you tell if the noise happens when the compressor engages? If so, the noise is the sound of refrigerant passing thru the expansion block. Sometimes this will occur if the system is low on refrigerant, so if you are able to tie it to the A/C system, I'd probably have it serviced to make sure it's full.

 

[blkprj80]

Cool, thanks Coolstream.
It does seem to coincide with the compressor kicking on, but I can't really tell for sure since it is usually moving when the noise happens.
I tried to convince myself it might have something to do with recirc, but nothing seemed to jive.
Interesting about the expansion valve. That would make much more sense since it seems to be coming from inside the truck, under the dash. My wife thought it might have even come from under the seat (wasn't me, honest!) when she was riding shotgun.
Is it damaging to run it for a couple weeks? The system seems to be working fine, just this noise. I can get cold vent temperatures of 42, but then again, we haven't seen the highs in the 90's here yet.
How much would a fair set of R134 gauges run? Hmmm, maybe I'll take a look that guy craig has on his list...
I appreciate the help Coolstream!