Know someone that has a Pontiac Grand Prix,Not sure of the yr. ,appox late 90’s,coolant is not low,thermostate was resently replaced,what should they do?
Check that heat is actually getting to the heater core. Once warmed up check the temp by feeling the hoses that go into the firewall. If both are warm then it is probably a blender door problem. If not there may be a flow control to the heater core that is not operating properly.
Is the heater core located on the driver’s side under the dash on these cars?Is the blend door attached to the heater core?
should be under the dash passenger side. The blender door is attached to the A/C box where the heater core is mounted.
If you get no response when turning the heater on at any number setting, it may be the because there is a leak through the hood cowl that drips onto the blower motor resister(?). Ours started out just not working on some settings, then finally none.