I have a 2002 grand prix se and the heat is not working, after a long time it will get slightly warm but thats it really.

Pontiac Grand Prix Climate Control/AC - Car Forums at Edmunds.com

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Fixing AC Temperature Control on my 2002 Pontiac Grand ...

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Jul 13, 2014 - Uploaded by Turbo231
Fixing AC Temperature Control on my 2002 Pontiac Grand Prix... How To Install Replace AC Heater ...

Here they are both 2 and 4 door diagrams!

The heater core is under the dash. Go to autozone.com and register with them. Look up heater core in repairs. They will give you free instructions on how to remove and install.

A couple of things comes to mind.....1, your Thermostat is not functional, as in it's stuck open etc. 2, the simple answer is the amount of fluid (water/anti-freeze) is low; make sure you have the fluids top-off. 3, you didn't say but if the air is or isn't blowing cold before it does get hot, maybe the vacuum line to the door to let the hot air come from your heater core is having a problem-or-the door itself is having a problem. Hope this helps,
P. Ford

try your switches. many time they get old and warm from use and may not be functioning all the time. try getting one from ebay or a junk yard.

2000-2004 impala easyest

Yes. But you also will need to change the transmission and the exhaust.

With the engine warmed up feel the heater lines going into the firewall. You will probably find that one is very hot and the other only look warm or even cold. If this is the case the heater core needs to be flushed. With the engine cold remove the hoses at a convenient location and back flush the heater core. Reconnect the lines and warm the engine back up with the heat on.

It is not very hard. You need to turn the bolt in opposite direction while applying pressure to the back side

for the fan blower motor it could be the resistor or the fan control speed control switch is bad.for no lights replace the DRL RELAY for the lights. for the heated seats check the fuses.