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Dear Jim,

I have a 2005 Pontiac Grand Prix (3.8L, V6) and there's a problem with the dual-zone air-conditioning system. The passenger-side vent blows cold air, but the air coming out the driver-side vent is hot.

I know the vent isn't blocked, because the hot air is blowing pretty hard out of the driver side.

Is this a problem with one of the compressors?

-- Mike Bonds

No, bro, this is a totally different thing.

Even though your Pontiac has dual-zone climate control, you still have only one air-conditioner compressor for both sides of the car. If there's cold air blowing out from anywhere, then you know the compressor is working, which is great, because those things get very pricey.

The culprit here is in the dash.

In older vehicles, often there's a problem with loose or broken cables that control the A/C vents, making them stay closed when they should have been open. In your newer car, there are no cables that control the vent doors.

Instead, you have electronic programmers that control two separate electric motors, one for the driver side and one for the passenger side. Those motors move the A/C vent doors to change the mix of hot and cold air that's coming out of the vents. It's very likely that the motor on the driver side is burned out, so the vent door isn't moving.

Cold air is being blocked from coming out of that vent, leaving you with a lot of unwanted heat.

That's how these dual-zone systems work. The same cold air is being generated by the compressor, but once it gets into the ducts, it can be split between the driver and passenger sides and mixed with different amounts of warm air to make two different temperatures possible.

It's funny that you can have two climates in such a small space, but it pretty much works, keeping people on both sides of the car happy.

Get that vent door motor replaced, brother, and avoid road rage when it gets really hot this summer.

Tip of the Week:

With the weather getting warmer, drivers, now's a good time to mention something important when test driving a used car. If it's hot out, make sure the heater works.

Same thing if it's chilly out -- don't forget to check the A-C. A lot of people forget to do this when it's not the right season.

Buffalo Jim, owner of Allstate Auto & Marine Repair in Las Vegas, writes a weekly column. Send your automotive questions to him at buffalojim@lasvegasniftynickel.com. If Jim picks your question to answer in Nuts & Bolts, you'll also be the proud recipient of a deck of official Buffalo Jim playing cards, presented in a classy, tin box bearing his hairy image.