Advance Answers: Questions About Vehicle A/C Systems

We explore a couple questions that have come our way regarding your car's thermostat and how vehicle air conditioning systems work.

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In general, using logic and common sense when diagnosing problems with your vehicle—and when making repairs and addressing issues—is a good strategy. You eliminate what doesn’t make sense as you narrow down your diagnoses. Every once in awhile, though, what you should do is somewhat counterintuitive. Especially when it comes to vehicle A/C systems (which are part of a vehicle's HVAC system, or Heating, Ventilation, and Air Conditioning).

What should I do when my car overheats?

Sometimes cars overheat (fortunately, not as often as they used to). This happens most often in hot summer weather—and if you’re in the car, you’re probably feeling pretty toasty yourself. The first thing to do is to shut off your car’s air conditioning and open the windows to decrease the burden on your engine. So far, that makes sense — but, the counterintuitive part is this: if your car continues to overheat, then turn on both your heater and its blower. It may be uncomfortable, but this transfers heat away from the car’s engine into the inside of the vehicle itself.

Why should I use my A/C system in the winter?

The best thing to do during winter is run your A/C. It sounds strange, but running your vehicle’s air conditioning system during the winter can make sense (just remember your gloves!). If you run your A/C throughout the year, the system stays more lubricated, helping to prevent leaks. That’s because the refrigerant contains oil that lubricates the system, including the compressor. It also keeps seals and hoses moist, which helps to prevent the dryness that leads to cracks and leaks in the system. Your car’s A/C system is also much more efficient at window defogging than the heating system. So, turn it on to clear up the fog—and, if your A/C doesn’t do the job, check the compressor because this might indicate a problem.

How important is it to fix the thermostat?

The thermostat is a relatively small and inexpensive part with an important job: it senses and "reports on" the varied temperatures throughout the vehicle’s engine. The engine needs to run hot to burn fuel, but if it gets too hot, the thermostat signals the release of coolant to reduce the temperature. If the thermostat isn’t working properly, the coolant can keep flowing until it’s all burned off, which can lead to overheating or even more severe problems, like a blown cylinder head gasket. In cold temperatures, the thermostat prevents water from going to the radiator. This helps the engine warm up enough, even on bitter winter mornings.

If you think your thermostat might be operating at less than optimal efficiency, it’s often easier to replace it to see if that solves your problem, versus going through more complicated diagnostics. Check the original thermostat in your vehicle and buy a comparable thermostat replacement. You can also check your owner’s manual to see which type of thermostat the OEM recommends.

Last updated July 11, 2017