Karen M. Asks: Why Won’t My Air-conditioning Turn Off In My Car?

In heat defrost mode.

Karen told me that no matter what she tried cold air was blowing out of the floor vents in her car when she was driving home from work one day. What could cause this? Well after I gathered more information from her it was not to hard for me to figure it out. I asked her what mode or vent position her heat system was in, she told me it was in the heat/defrost mode position from earlier that day. You see when you activate your windshield defroster or in heat defrost mode it turns on your A/C system. Your A/C system actually assists the defroster by removing moisture from the interior of your vehicle. Years ago it confused people when they used their defroster and the “A/C” light would illuminate and then they would turn it off , thinking that something was wrong the system for the A/C light to come on like that.  In later model vehicles of today the A/C light will not come on when you choose the defrost mode. So what happened to Karen was the vent position was in the heat/defrost position from earlier that day. When she turned the temperature control down the the A/C was actually still on because it was in the heat/defrost mode. In other words if she chose the vent or floor position the A/C system would have shut off and her feet would not have gotten  so cold. This another good reason for people to reference their owners manual that is hidden in the glove box. Dig your owners manual out of your glove box and read some of it. You just may be surprised as to what you don’t know about your car.

In heat defrost mode.

In heat defrost mode.

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