Heater is blowing only cold ear when redusing the heat controller.

Clicking sound you hear is the worn brushes in your blower motor. At this point the blower moter may or may not start with the switch. THe blower motor is faulty so I would change that first, then check for vacuum leaks or faulty selector cable for the heat blend door. It could have came off door side or heater control side.

Could be air in the cooling system , try an bleed the system . On top of the thermostat housing is a bleeder valve , with the engine up to temp. open valve till coolant comes out . Is the coolant full ? What color is the coolant ? Have see where coolant turns like a muddy color an clogges the heater core an engine coolant passages . Check the heater hoses going into the fire wall ,are they hot ? Does your grand prix have manual or automatic climate control ? Duel zone ! Do you hear a clicking sound behind the instrument panel ? Bad temp blend auctuator .

Check engine coolant if it is low it will cause the heat to blow clod. make sure and check it while cold. also if it only last a second or two that is normal the heat controler is in many cases operated by vacuum.

Hi you old horse, make sure the control valve which allows heated coolant from the engine is operating correctly. Regards Jongee10

Sounds like the blend door or blend motor is not functioning/opening. This door allows the heat/cold air to come in by adjusting open, closed or anywhere in-between for temp. Start there. They are usually vacuum controlled and mounted under the front dashboard near the knee board.

Hi John,
Your right with your diagnostics, you have a blend door problem. If your switching to cool air and it is still hot then you also have a heat exchange unit fault, this is the component that changes the water flow from hot to cool by shutting off. If it is not operating correctly this will give you constant hot air no matter where you temperature switch is positioned.
As for the warm air while the engine is cold, sounds like the blend door is still open to atmosphere tempreture and if it is hot outside will pull that hot air into the inside of the vehicle.
Have the heat exchange valve checked, and the only way the check blend door operation is to remove the wiring from the blend doors and have the circuit tested. If the circuit is ok then the blend doors will need to be replaced.
Hope this helps

check coolant level, if ok change thermostat, it may be sticking.

Check the temp dial, the potentiometer may be faulty

After warmup it still blows cold, or only when cold? Normally the fan will operate independently of engine temp except in some climate controlled vehicles. As long as it blows warm air after engine is at temp that's a good thing. the heater uses hot water from the engine. Obviously the heater can't be warm before the engine is. If it's cold after the engine is hot, there are vacuum controlled "motors" on top of the heater box under the dash that move doors that control heat. Either one of the control motors or one of the doors have stuck or failed. Many also have a control valve on one of the heater hoses under the hood as well. If the engine comes up to temp then the thermostat is good (should be at about 210f) Only remaining item is the core itself which may be internally or externally obstructed.
All this being said, if it's good when the engine is up to temp, leave it alone...it's fine.

Sounds like a stuck heater core valve. Find heater core valve. Under hood, find the two heater core hoses going into firewall. One of the hoses has a valve. Operate temperature control (full heat, then full cold) check that valve changes position. If not either replace valve or control system failure. Also, when temperature control in cold position, one hose should feel hot and the other cold. Temp fix: disable valve to close no heat or on heat.