Heater problem
1993 Mercury Cougar 6 cyl Two Wheel Drive Automatic

I have a 1993 mercury cougar that runs great but there's a slight problem with the heater. there is none. I really cant figure out what it is but here's the lowdown on what it does

the buttons work ok but the the off button sticks
there is a hissing noise when i turn on the other switches but no heat

the compressor works great

the radiator full and topped off

the thermostat is stuck open

thank you for your time