I have already put refrigerant in my 1994 mercury sable but it still blows out hot air.

Not in the coolant system, you flushed

It is a failed HVAC Blend Door Motor, under the dash

The fact you have heat or A/C, but not in all 5 positions
or combinations, should have told you, the air flow is not
switching as it should

Could be a blender door issue. What a blender door does is mix the cold air from the AC with the hot air from the heater core. If you put the switch ALL THE WAY to hot, the blender door (usually an actuator) pushes the door up and allows only air passing thru the heater core to enter the cabin. If you push all the way to cold, it only allows air from the AC. If you put halfway, it mixes/blends the air...

Check that the wiring for the compressor clutch is connected. Have the system checked for the correct amount of gas as too little or too much will stop the clutch of the compressor. If the old compressor failed and the system didn't have a new receiver/dryer fitted there is every possibility that the tx valve is blocked. have the pressure in the system checked while running.as a blockage will switch off the clutch also.

I'd have to say it's the blower motor. Does it blow hot air when the heater is on?

http://wiki.answers.com/Q/How_do_you_diagnose_and_fix_heater_blend_door_problems_on_a_Ford_Taurus_-_Mercury_Sable

2000 mercury sable
Try this link here, it's very helpful in repairing your vehicle

if the compressor works and your freon is charged it may be the blower flapper door....disconnect battery for 10 minutes and then re-connect to reset the electronics that control the flapper

Try to fixed it first try to check the water pump maybe you need to replace the water pump that's why you are running hot.

I’m happy to assist further over the phone at https://www.6ya.com/expert/ramy_d9e7ebea3891f482

CYCLING COMPRESSOR COULD MEAN TOO MUCH OR TOO LITTLE FREON.TAKE IT TO AN A/C SHOP

you have a broken or stuck temp blend door in the heater case. or the servo motor is broken. this sits on top of the heater case