I seem to be having a hiss sound coming out of the AC recently. Cruising speed and at acceleration it doesn't happen. But when sitting idle or sometimes on deceleration I will get it. I'm still getting decent cold air. I picked up some r134a, and put my pressure gauge on it after the engine warmed up. I ended up not adding any Freon cause the pressure didn't seem to be low. What else should I start looking at?

Thanks

 

You probably hear a vacuum leak. Many of the doors that change the air from going up to the vents or down to the floor use vacuum motors to move the flaps; in other cars that I've worked on anyhow, I haven't worked on this van's HVAC.

 

Or you have a snake in there and it gets angry when you make it cold. :-)