Your car's defroster uses air conditioner

  • Article by: PAUL BRAND , Star Tribune
  • Updated: September 8, 2010 - 3:53 PM

Q I have a 2007 Subaru Outback. Earlier this summer, it was raining on the way to work, so I put on the defroster to clear the windows. As I was driving home, I was pleasantly surprised at how nice and cool the car was. I congratulated myself on another day without turning on the A/C when I realized that the car was cool because the defroster was still on. Ever since, when it's hot I drive a few miles with the windows open to cool down the car and then shut the windows and turn on the defroster.

Is this hard on the defroster? Am I being green and saving any Freon? Or is this just another way to use the air conditioner?

A Just another way to use the A/C. The "bi-level" setting would probably be even more comfortable because some of the cool air will be directed at you, rather than the windshield. Why sweat or fret? Be cool and confident that you're not using up or wearing out the refrigerant or wasting fuel -- your comfort is worth the very small extra cost.

Q When temperatures are below 30 degrees, my '95 Mercury Mystique has to idle for 30 minutes or more before it will shift out of park. The dealer told me that since it shifts fine when I bring it in, they can't fix it. I have begun leaving it in neutral when I park, but then the key won't come out of the ignition. Please help!

A Hmm ... if you leave the doors unlocked with the key in the ignition, maybe the problem would "disappear." And I can't help but wonder why the dealer didn't suggest leaving the car overnight so they could try a cold start.

But there may be a relatively simple explanation and answer. On a cold start, check that the brake lights come on when you step on the brake pedal. When the key is turned to "run," the shift interlock solenoid is activated, locking the shifter in park. When the brake light switch is activated by pushing the brake pedal, the shift interlock solenoid is disengaged, allowing the shift lever to move out of park.

Q When my 1991 Honda Prelude is left out in the heat, it cranks over but will not start. If I open the hood and let the heat dissipate, it will eventually start. One time I sprayed it with cool water and it started up, but I was afraid to continue doing this for fear of getting something wet that I shouldn't. I have also had the same problem on cooler days after driving a short distance, turning it off for a few moments and returning to the same symptom.

A Two words: vapor lock. Fuel is boiling or percolating in the fuel system, causing a loss of fuel pressure and the subsequent no-start condition. You proved this by cooling the fuel system with water; presto, the car started.

The temporary fix might be allowing the engine to idle for a minute or so before shutting it off. This will carry some of the residual heat from the engine into the radiator, where it can dissipate. Also, pop the hood open to the safety catch while the car is stopped to allow heat to escape from the engine compartment. Remember to close it before you drive off.

A full cooling-system cleaning, flush and refill service, along with clearing debris from the front of the A/C condenser/radiator and cleaning any grease buildup from the engine, will reduce the heat buildup under the hood.

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