Chevrolet Repair: 1994 Chevy Lumina heater nightmare, vacuum servo, vacuum leaks

Question
The heater blower works fine, can select high, low, etc., can choose vent, floor, bi-level, etc., all works fine.
The problem is you cant turn it off! if you turn the blower off, heat still comes through.  If you turn the temp to cold, heat still comes through. We removed the a/c pump and replaced with a dummy pulley and it still does this. My husband is replacing the thermostat in the morning but what could this be?

Answer
HI DEANNA, STOP THERE,TELL HUBBY DONT REPLACE THE T-STAT..THE PROBLEM IS IN THE DASH CONTROL HEAD CONTROL OR FAULTY BLEND DOOR UNDER THE DASH. THE BLEND DOOR IS NOT CLOSING OFF THE HEATER CORE SECTION WHICH IS ALLOWING HEAT TO GET IN THE CABON AREA..THERE COULD BE A DOOR THAT IS STUCK BECAUSE THE GEAR THAT CONTROLS IT IS BROKEN OR THE DOOR IS NOT RECIEVING A SIGNAL FROM THE DASH CONTROL OR VACUUM SERVO. THE BEST ADVISE I CAN GIVE YOU WOULD BE TO REMOVE AS MUCH PLASTIC SHIELD UNDER THE DASH SO YOU CAN SEE THE CONTROLS TO THE HEATER AND AC/DUCT WORK..MOVE THE TEMP CONTROL ON DASH AND SEE IF YOU CAN SEE ANY ARMS OR PIVOTS WORKING UNDER THERE. YOU MAYBE ABLE TO MANUALLY CLOSE THIS DOOR IF YOU CAN GET TO IT..THIS MAYBE A PAIN IN THE TAIL BUT WORTH A TRY..ALSO MAKE SURE THERE ARE NO VACUUM LEAKS AT THE ENGINE SIDE THAT SUPPLY VACUUM TO THE DASH BOARD HEATER CONTROLS.. GM USES EITHER ELECTRIC OR VACUUM CONTROL SERVOS..ON A 94 CAR I THINK IT IS VACUUM..IF THERE IS A VACUUM LEAK AT THE ENG AREA,IT WILL NOT SUPPLY ENOUGH VACUUM TO OPERATE THE DASH BLEND DOORS..I HOPE THIS HELPS YOU....