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I have a 2013 Subaru Outback. The A/C makes a subtle but irritating whistling noise when the outside temperature is between 13 and 20 C. When I turn off the A/C, the noise goes away. I read online that this may relate to the A/C expansion valve and that the sound is normal. The Subaru dealer and one other garage have not been able to help me and have changed out the drive belt and various pulleys etc., which have had no effect.

Thank you. Colin S

The expansion valve is located in the dash, whereas the drive belt and pulleys are under the hood. The previous repair attempts suggest that the technicians are concentrating their efforts under the hood.

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The expansion valve does exactly what it says it does by removing pressure from the liquid AC refrigerant. It does this with a movable valve and rod that travels up and down within the valve, allowing for expansion. These valves are indeed known to hiss and, to a lesser extent, whistle. The first thing you need to do is determine whether the noise is in-cabin or under the hood in origin. Under-the-hood noises are typically solved in the manner that you have already experienced.

Keep in mind that any A/C system that has an incorrect refrigerant level will suffer in a variety of ways. One of them being an expansion valve that may develop weird noises due to it being overworked. If the noise is determined to be in-cabin, be sure to have the pressures and refrigerant levels verified before proceeding to expansion-valve replacement.


I drive a 2010 Subaru Forester which has 200,000 kms. The dash left-turn light comes on and stays on when I turn on my headlights. Figuring this to be a warning that a left-turn signal bulb had burned out, I checked, but both front and back signal bulbs were winking. The interior left indicator winks dimly. Does this indicate an expensive problem, or is it something I can live with?

Doug R.

Automotive techs have countless stories of the weird faults they discover perpetrated by well-meaning DIYers. A common one is the replacement of a burnt-out bulb with the incorrect bulb. Grandpa always a left-over bulb from his ’84 Buick in his dusty garage collection that looks just right and gives it a try. I’m not suggesting that is your situation, but it’s worth a mention.

That being said, the first thing to do is check all the bulbs for the correct type and that they are seated in their sockets correctly. If you are feeling really ambitious, swap the turn-signal bulbs from the left side of the vehicle to the right and see if the right indicator now winks dimly.

However, that the problem occurs when you turn the headlights on suggests a bigger problem. Namely, that the turn signal and headlight circuits are no longer isolated and power is bleeding from one circuit to the other. This could be a simple connector-corrosion problem, or the combination headlight/turn signal switch has failed. I’m sure you can live with it temporarily, but corrosion issues will usually get worse.

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Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing “Lou’s Garage” in the subject line.

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