noise from AC

["Joe B" <jsjb100@xxxx>]

Hi folks

My AC had an R12 to R134a conversion, blows cold, seems to work fine. 
One question...when I first start my car for the day, if the setting 
is on vent and i shift it to bi-level there is a loud groan lasting 
about 3 seconds that comes from under the middle of the dash. I 
cannot reproduce the sound any other time during the day, just upon 
the first start. Once again, the AC seems fine, no other unusual 
sounds or smells.

Any thoughts?

Joe B.