Noise from Evaporator/Blower Area

[DBMaster]

I have been hearing an intermittent "hissing" noise from the evaporator/blower area behind the glovebox. It will sometimes occur when I go over bumps. It is only occasional, but I have confirmed it makes this noise even when the A/C and blower is off. I am thinking it may be a leak in the vacuum motor that controls the vent doors, but I wanted to see if anyone else here had experienced anything similar before I replaced the part.

Thanks!

[LX-incredible]

The vent motors are electric... Does this only occur going over bumps?

[DBMaster]

As a matter of fact it often starts up after hitting a bump (but not always), but it happens with the blower and A/C off. At first I thought it was a noisy expansion valve. I was thinking vent motor because my old Pontiac had vacuum operated vent doors. I checked the blower motor and the bearings/bushings are still in great shape so I am very perplexed. It is making the noise more frequently and it seems to be getting louder.

[DBMaster]

I guess this is one of those rare things that few have experienced?

[Hazwan]

Leaks on AC lines maybe?

[nswst8]

Check your a/c pressures my expansions valve threads were leaking one of the culprits for losing freon.

[DBMaster]

I have had to add about a half can of R-12 a year since the car was new. I replaced the compressor, hoses, and drier in 1999. I am thinking that the expansion valve should have been replaced with the other stuff ten years ago, but it is weird that I will sometimes hear the noises even with the compressor off. I guess as the engine compartment warms up Freon can still move around the system even without the compressor running.