2006 Pontiac Grand Prix Heater blows cold / cool air at idl

DOBER6972

MEMBER
2006 PONTIAC GRAND PRIX
6 CYL
FWD
AUTOMATIC
70,000 MILES

I have recently started to have this issue with my car this last year. My heater does not blow hot air when idling, but blows warm air when running. Basically, idle speed the temp is cool even with the climate control set at 90 degrees, air is cool to cold. The air only warms up when driving at 45 mph or higher. As I go faster, the hotter the air. I have dual climate controls and I set it on 90 degrees.

I have had the several thermostats put in. I have plenty of anti-freeze in the system. I have had the heater core flushed and back flushed numerous times, a new water pump. They also flushed out the block twice. The hoses in and out of the heater core are both hot when car is at temp. The blower fan works fine on all speeds. I have had my cooling system bled twice. I am I going crazy?

Can this be an issue with my blend doors? Is my climate control sensor bad?

I notice that when the RPM's are above 1500-2000 the air does seem warmer, but any RPM below this and it is cool to cold air coming out.

There are no external leaks of anti-freeze, no leaking into the cabin of the car on the passenger side, also, there is no traces of anti-freeze in the oil or transmission fluid either, both are nice and clean. The operating temperature is normal, it is not over-heating at all and is operating within the normal range for this engine. 180 - 195 degres Fah.

I also noticed that everytime I start my car, the air conditioning bottom is lit up, idicating that it is on. I have to push the button off everytime I start the car. Could this indicate an issue with the cabin climate control?

It is a 3800 Series 3 supercharged V6, the GT model.

2 Replies

RACEFAN966

MECHANIC
5,029 POSTS

I would say either blend door issues or a vacuum control valve, heater control valve or a vacuum hose to the heater system is leaking.

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Thursday, January 15th, 2009 AT 10:49 AM

JAMES W.

MECHANIC
2,394 POSTS

You have already checked all the things I would start to suggest. You are correct in checking the blend door. A computer scan should tell you what temp the climate control thinks it is in the passenger compartment. It may be a thermostat problem giving the climate control a false reading. Your blend door is controlled by a servo motor under the dash. You can remove the servo and watch to see if it moves when you change the temp setting from heat to cool. Also, you should be able to manually move the door to the heat position and see if you get heat.