Dear Car Talk:

I have a 2017 Honda CR-V. Whenever I return from a long road trip (1-3 hours) and my air conditioner has been running, I hear a prolonged whistling sound (for 1-2 minutes) after I turn off the ignition.

The sound is coming from under the hood on the passenger side. It sounds like a compressor draining air. I took my Honda in for servicing, but they could not replicate the sound. It only occurs after long use.

I want to get it taken care of, as I only have 5,000 miles left on my warranty.

Any suggestions? -- Jack



Yes, I suggest you stop hanging around your car after you shut it off, Jack.

When you run your air conditioner, the compressor "pressurizes" your refrigerant. So, when you arrive home after a long drive, that refrigerant is under very high pressure.

Once the air conditioner is shut off, which happens when you shut off the engine, the refrigerant needs to return to normal pressure. And it does that by passing through something called an expansion valve. I think all you're hearing is the pressure of the refrigerant equalizing by passing through that valve. It produces a soft whistling sound while it equalizes.

Unless it's really loud, or whistling a funeral dirge, I don't think it's anything worth worrying about, Jack.

If you were to shut off your air conditioner while you were driving, the same thing would happen. But that faint whistling noise would be drowned out by the road noise, the engine and the argument you were having with your wife about why you turned off the darned air conditioner.

Find a reason to do something else when you get home. Preferably something that doesn't require you to be in the garage.