It’s getting hot out there: A look at your air conditioning system

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There are not many things that top that feeling of entering a cooled vehicle after any time out in the heat. And as we have finally experienced our first week of temperatures above 50 degrees (with that 80 degree day on Saturday!), you’ve already had the privilege of entering your car in the afternoon and endured those sweltering cabin temperatures (or rode around with the windows down) until your air conditioning system could catch up and start cooling things down.

That is, if your air conditioning system is working. And as we head into the holiday weekend marking for most of us, the beginning of “summer,” you don’t necessarily want to keep warm, do you?

How it all works

One of the most common misconceptions surrounding air conditioning is how the air is actually cooled. Yes, there is cold air coming through your vents, but it’s a little more involved than that.

Refrigerant (freon) is guided through the A/C portion of your HVAC system in two different states: liquid and gaseous. In this cyclical system refrigerant is found in a gaseous state, where it is then drawn through the compressor at a low pressure and pumped out as pressurized gas to the condenser.

The condenser takes the gas through its winding pipe system to remove heat, in which the condenser (near the front of your vehicle) will radiate the heat. The removal of the heat from the system “cools” the refrigerant into a liquid state (note there is no actual application of cold to cool the air). It is then passed through desiccants in the receiver drier that attract water, to prevent ice crystals from forming during the cooling process and damaging the system.

That moisture then collects on the condenser and the expelled moisture is the culprit behind creating those puddles underneath your car. Ever notice on a really warm day when you’re using the air conditioning, the puddle is bigger? More heat and humidity = more heat to exchange and moisture to remove = larger puddles.

The last parts of the system takes the liquid coolant through an expansion valve that expands pressure to allow liquid to be prepared for the evaporator. The evaporator, will take on the heat from your cabin to heat the refrigerant to a gaseous state, and the process begins again.

To simplify it, the A/C system removes heat and moisture from your vehicle’s cabin which in turn cools the air.

Also, keep in mind the cabin air filter, which we delved into this in “To breathe or not to breathe: Reasons to change your cabin air filter this season,” is a part of the HVAC system that involves your air conditioning. Not only is the air coming through the vents going to be compromised by a dirty cabin air filter, but your air conditioning system will have to work harder to filter air through the cabin, as the air cannot pass through the filter efficiently. 

And an inefficient A/C can (and will) leave more moisture in the air, lending the way to collecting on your cabin air filter, and creating a musty smell from the mold that has formed.

How to spot a troubled A/C

  • Hot air blowing from air vents when A/C on/selected
  • Little to no air blowing from air vents
  • Difficulty clearing  steamy windows and windshield when utilizing defrost setting
  • Odd fan noises
  • Musty odor

Some causes of a failing A/C

  • Leak in A/C system
  • No freon/refrigerant
  • A dirty or clogged cabin air filter (look back to our post on it here)
  • Failure of condenser, or evaporator, or compressor or any other intricate part in the system.

When in doubt, charge your A/C

In many cases where a leak is possible, but the culprit has not yet been discovered, a dye will be added to the system. After a certain amount of time (determined by your technician and service advisor), the vehicle is brought back into the shop and combed over to find dye in spots where there is leaking in your A/C system, and repairs can be made from there.

(*Note: Your self or someone you know have probably thought there was an actual charging (like a battery) component. That is not the case. Charging is the replenishment of refrigerant into your vehicle.)

So when to bring it in?

If you’re experiencing any of the earlier mentioned symptoms in your vehicle, it may be time to bring it in for a diagnosis, so the problem can be found and mended.

That is, unless you are prepared for a summer with your windows down. However, from experience, it is not so ideal when on those hot, humid and rainy summer days.

And if you are more of a visual learner, Donut Media’s Science Garage produced a great short episode on the workings of your air conditioning and HVAC system.


“For the Miles Ahead” blog is a weekly series dedicated to demystifying automotive maintenance and service needs for the friends, family and customers of DeNooyer Chevrolet. If you have a question about service maintenance or car-related troubles, write to Motor Maven at MotorMaven@denooyer.com, and it could be included in the next week’s publishing of “Ask Motor Maven.”

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