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98 Buick Temperature control works passenger side but not driver side


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dumndac
New User

Nov 12, 2018, 9:36 AM

Post #1 of 5 (170 views)
98 Buick Temperature control works passenger side but not driver side Sign In

1998 Buick Century Limited, 86k, 3.1L: It's winter and I would like hot air to come out of both the driver side and passenger side middle-level vents. The problem is that cold air comes out of driver side and hot air comes out of passenger side. Adjusting temperature functions for passenger side but not driver side. Here are some clues:

- No amount of fiddling with the HVAC buttons in Auto or Manual mode seemed to fix the problem. Most of my tests were in manual mode because Auto mode seemed to behave the same. Also DUAL mode was OFF during these tests.
- Changing the temperature changed the temperature of the air on the passenger side but the driver side remained cold and unchanged. When temperature was set lower, both side would push cold air. At max high-temp, still cold air on driver side and then passenger side back to hot.
- I performed a 'reset' by disconnecting the battery for an hour
- Upon re-connection, the first thing I noticed was that the yellow Auto button light on the HVAC head was working. This wasn't working before.
- The second thing I noticed that the fan wouldn't come on. By fiddling with the buttons for 5 minutes, the fan came on.
- However, as soon as the fan came on, lo and behold, I got hot air coming from both driver and passenger side vents!
- To verify that this was not just a one-time fix, I turned the car off and then on.
- Immediately the original problem returned: cold air on driver side, hot air passenger side.
- The fan was also hard to start but I noticed that if I removed and put back the blower fuse, the fan would almost always start working again. (The fan is more of a red-herring....the temperature problem is the main thing I need to solve.)
- Btw, somewhere along the way the Auto button yellow light stopped working again.
- I noticed something weird: When HVAC was off, whenever I pushed a button to turn the unit on, I could hear the engine strain. It acted like, no matter what, the A/C compressor was turning on (even though the temperature was set to max-high and it was cold outside).
- Sure enough, I noticed the A/C clutch would engage whenever a button was pushed on the HVAC. I removed the fuse for the A/C clutch.
- From this point on, the compressor did not engage, however the driver side vent continued to blow "cool" (but not cold), presumably outside air. Passenger side still hot.
- During testing, somehow, magically, after the HVAC was on for about 10 minutes, the driver side started blowing hot air.
- I turned car off and then on, and the problem returned immediately. The driver side blowing cold air, passenger side hot
- This morning on way to work, I waited to see if the driver side would magically start blowing hot. It didn't.
- Then, after about 10 minutes, just on a hunch, I lowered the temperature as low as it could go, and then raised it again to max
- Voila, both sides start blowing hot air.
- My question: Is there a driver side thermostat separate from the passenger side? If so, it seems like the driver side thermostat always thinks that the temperature is "too hot" and thus turns the A/C on and then channels the A/C cold air into the driver side vents because it thinks it should be cooling the driver off even though it should be heating him up. Also, apparently, even when the A/C clutch is disconnected, it puts some flap in position to channel air from the A/C to the driver side vent, rather than channel air from the heater.
- At first thought, one might think that the driver side actuator that controls a flap may be at fault. However, if this were true, why would the HVAC be initiating the A/C clutch when it shouldn't? If it was just a flap actuator problem and the thermostat was working properly, the A/C clutch would not be engaged, but the driver side would blow "cool" (outside) air.

Thoughts/theories welcomed.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Nov 12, 2018, 9:57 AM

Post #2 of 5 (167 views)
Re: 98 Buick Temperature control works passenger side but not driver side Sign In

Arg! You've had it working twice I think in that description of the trouble so it's going to be guessing only till it stays broken IMO. Actuators and the "flaps" are pretty cheap and have been for ages and you are there now 20+ years.


It's possible the way it senses air temp most frequently pick up/sense interior temp pulling air from out of the way down below and up thru high in the dash near impossible for me to tell you where look for something that could do that.
Depending on actual ambient temp OUTSIDE compressor should not really be working or compressing I think this one can turn like it is but isn't really working hard it can't by a certain temp and shouldn't so that isn't it alone.
Two things. How it senses the temp is achieved and need to almost get a scope to view actuators working and hope flap/diverter doors are not stuck from wear.


Blower: Can you see the body of it? Give it a whack just with a smaller rubber hammer when it quits high chance it would come back on if easy enough just do that if rare for now the fix would be a new blower motor usually,


T



Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 12, 2018, 12:11 PM

Post #3 of 5 (164 views)
Re: 98 Buick Temperature control works passenger side but not driver side Sign In

Why do people always think disconnecting a battery will fix something?

Most often it makes matters worse, as in your case.

Your next step should be to have someone with a professional scan tool, not qa generic code reader, retrieve the stored codes in the AC system.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



dumndac
New User

Nov 13, 2018, 10:28 AM

Post #4 of 5 (128 views)
Re: 98 Buick Temperature control works passenger side but not driver side Sign In

Thanks for your input, much appreciated.

Am I correct in saying that the blend door is responsible for mixing hot and cold air to achieve the correct temperature? If so, are there typically two blend doors actuators if the car has dual-side climate controls (driver & passenger side)? I've been searching parts lists and have not found a definitive answer. I know there are two types of actuators for auto vs. manual climate control, but I get conflicting answers on whether there are two blend door actuators in the system, one for passenger side blend door and the other for driver side blend door.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 13, 2018, 4:58 PM

Post #5 of 5 (122 views)
Re: 98 Buick Temperature control works passenger side but not driver side Sign In

Yes, if you have individual temp controls, then you have 2 blend door actuators.

Don't automatically assume the actuator is the cause of the problem. The door itself cam be jammed or broken. The control head can be giving incorrect commands, the wiring can have an issue also.

The actuator needs to be accessed and examined when the temp is changed to see exactly what is happening. When you disconnect the battery the system goes into a self calibration cycle. That itself can cause issues because it forces the doors to it's limits to calibrate. Sometimes when these doors are forced to places they have no been recently, they can get stuck.

Here is a picture with locations





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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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