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99 Buick Regal GS Heater problems

11-07-2007, 01:17 PM
Hey guys, getting cold and my heater is not working. The two hoses going to the heater core are hot after running and the fan runs but nothing but cold air comes out. I have the auto-temp so I am assuming it is a computer issue. The radiator is full. I don't know what else to check. Any ideas??

11-07-2007, 01:31 PM
Welcome to AF.

Sometimes the ACC unit hangs up and loses reference or feedback to the temperature control actuators. Two - one for driver's side and one for passenger side. Turn ignition to on and then manually turn off the ACC and then ignition to off. Remove the battery negative cable for several hours. You may have to repeat this a few times. The GM dealers have a firmware update for the HVAC controller that is supposed to resolve this issue. If this doesn't work then check the fuses to the climate control unit and whether the temp actuators are responding when you vary the driver's and passenger temperature setting on the ACC unit.

11-07-2007, 01:46 PM
Thanks for the quick reply. I just turned the ignition on and the acc was already off. I turned the ignition off and unhooked the negative from the battery. I will let it sit for a while and give it a try. I am going to try to flush the heater coil if this does not work. The hoses were not very hot so maybe it is partially clogged. I will check the fuses then. Thanks for the tips and I will let you know how it goes. One other thing I noticed was the "change oil soon" light was on but there is plenty of time left before the next oil change. Probably a coincidence.

11-07-2007, 01:53 PM
Thats interesting. The oil change indicator system is not that dependable but one of the parameters the PCM module looks at is engine operating temperature so it may not be coincidental.

If the heater core input doesn't feel that hot then you may have a simple thermostat problem. Probably stuck partially open but temperature gauge and warmup may still appear to read or be normal. I would pull the thermostat and visually inspect it. Then you can do a cooling system flush or just try bleeding any air out of the system after TS is removed and reinstalled.

11-09-2007, 08:18 AM
Well, nothing I have tried has worked. One thing is did not mention, I took it to Valvoline for my last oil change. The guy looked at my intake filter for the ventilation. I told him not to change it but when he put it back on, he did not put the weather stripping back on the bottom of the windshield. It rained hard that night and the water from the windshield ran into the intake and filled up the passenger floor with water. I am thinking it corroded the doors that move to control temperature and now they are stuck in the cold position.

11-09-2007, 08:56 AM
The actuators are high in the HVAC system, so water intrusion isn't a possible cause. That could cause the blower motor or module to go bad, as they are in the bottom of the heater box. I agree with Bob (Bnaylor) that it may be simply a thermostat stuck open or opening too soon causing the engine to not build up enough heat.

11-09-2007, 09:32 AM
I have never changed a thermostat before. I am pretty handy, is this something I can do on my own? How much will a new one cost? If possible, send me some instructions to Thanks a ton guys, I really do appreciate it.

11-09-2007, 09:57 AM
Here is a link from the Grand Prix forums for a t-stat proceedure. This one covers the 3800 series-II, but the supercharged engine (that I believe your GS model has) is similar. The part should cost less that $10.

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