i have a hissing sound coming from the dash

The heater still works but i cannot select destination for the vents i had to replace a fuse the other day, i took the heater/rear demister fuse out also. the heater and destination selector were working fine before fuse was removed. now the selector makes different "loudness" hissing sounds when i try to change destination, but will not demist front window, come out vents etc.

It appears only to blow heat at the floor. hissing sound also gets quieter under acceleration. also rear window demister no longer works, all fuses appear to be in good working condition. i thought it could possibly be a relay but have had no luck locating it. please help
thanks greg