1993 Mercury Cougar

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
December 21, 2008.

Hissing noise indicates vacuum leak. Check vacuum hoses for any signs of leaks. Replace thermo.

Dec 21, 2008.