A/C Heater issues

[treborr23236]

2001 Monte Carlo: A/C and Heater blower cuts off and on sometimes and is not warming the air out of the vents sometimes. Also when the car is off and keys out, I can walk by and hear the A/C heater blower come on and cut off again.I've heard it even after the car has been parked for hours! Any ideas on any of these things?

[DrRadar]

Sounds like three issues: (1) Heater not heating (sometimes), (2) intermittent blower with engine running and ac/heater on; (3) blower sometimes runs when key is out.

I'm going to assume that the 01 Monte Carlo a/c is similar to the Grand Prix. I think that's pretty accurate although some details may be different, like component locations.

Do you have manual or automatic control? Do you have one zone or two (driver and passenger)?

What is engine temperature when not heating? If the engine is warm, hot coolant must be flowing through heater core unless it is blocked (not the most likely problem, imho). If coolant is flowing through core and still no heat, then maybe the blend door is stuck in heater bypass position. If two zone, is vent temperature the same on driver and passenger side? I think the blend door motor is electric, but it could be vacuum; if vacuum, then there may be an open in the vacuum source (cracked/broken vacuum line). There should be a vacuum line going to a vacuum reservoir; on my 99 Grand Prix, it's accessible from the passenger side under dash, behind glove compartment.

An intermittent blower can be caused a motor going bad (brushes losing contact), the control head sending intermittent signal, or a bad blower motor resistor or module. Blower motor should be behind glove compartment on passenger side. You're going to have to troubleshoot. Try checking the input voltage to motor when it's not running but should be. trace back from there to blower motor resistor/module.

A blower motor running with key out indicates a major electrical malfunction. Something has to be shorted/failed to get voltage to the blower. Are you sure it's not the cooling fan? A cooling fan can run with car off when the engine is hot...but certainly not hours after it was turned off. If it is indeed the blower motor running with key out, your control unit may be malfunctioning in a big way, which could also be the cause of the other problems.

Good luck.

[treborr23236]

Water temp normal when not heating, so i'm going to try a new thermostat. After reading through a few threads, I'm going to replace the blower resistor. Its not the radiator fan running, its def. the heater as i've been sitting in the car waiting at the grocery and heard it come on and blow numerous times. Thanks for your imput,hope its not major elec stuff going on. will follow up on this thread as I do repairs.

[DrRadar]

Thermostat is an easy fix to try. If stuck closed, then i would expect some engine overheating when run long enough. But a stuck open thermostat could prevent coolant getting warm.