Ac Vents Scream

WEIRD PROBLEM.. at slow speeds or it seems, slower compressor speeds, SOMETHING inside the cab (vents, flap, whatever) will SCREAM LIKE HELL.

Stops instantly if I turn off compressor. If I am at speed and turn it on, no problem.

Vacuum?? Loose serp belt on compressor?? It's NOT in the engine compartment for sure. I have relocated the vacuum bottle but the issue didn't actually appear until I did a replacement of my condensor and hoses and a fill of the system with 134a.

Ideas??

ALSO: Has anyone replaced their vacuum lines and their CCV lines with Silicone tube?? My vacuum lines are very brittle!

Check the blower, try heater and see what happens when the blower is running.

I had that same problem for years. It drove me nuts. I just recently got a full flush (vacuum plus new oil and r134a) and it works like a dream. My problem was from inside the cab too, not to be confused with a sqeeling belt. It was excessive vibration in the lines that caused the rancid noise.