AC on the brain, it’s that time of year

Ron Nutini is a licensed automotive technician in Trail

Pardon me but I have air conditioning on the brain. Must be the heat. A recent recurring complaint from customers is the speed at which their vehicles cools down inside. NOT FAST ENOUGH!

When we are presented with a slow to cool down or not cold enough complaint yet we feel that the AC system is functioning close to what we might expect it is time to go to the books (computer) and see what the manufacturer of the vehicle designed the vehicle to be capable of. Usually the manufacturer’s air conditioning performance test will give a procedure and expected results. These tests vary by vehicle but are generally similar. They require that the vehicle be put in a certain condition with the AC on and some measurements are performed.

Typical conditions will be engine running at 1500 rpm. AC setting on MAX. Fan set on the second highest speed. Windows and/or doors will be open. A thermometer will be placed in a specific vent in the dash and pressure gauges will be connected to the high and low side of the refrigerant part of the system.

After leaving the vehicle running for a set period of time (conditioning) the measurements will be made. The expected results will typically be presented in a graphical format.

Ultimately your vehicle’s AC system was only designed to remove so much heat from the air. Moist (humid) warm air contains more heat than dry warm air. Therefore the temperature of hot dry air will be reduced more than hot humid air.

The expected pressures and temperatures will be based on ambient temperature and relative humidity. For example the vent discharge temperature (the air that is blowing on your face) maximum for a 2012 Chevy pickup when the outside ambient temperature is 30 to 35 degrees celsius is 17 degrees celsius at 30 per cent relative humidity. At the same ambient temperature but with above 50 per cent humidity you can expect a maximum of 20 degrees celsius.

If your vehicle is producing the correct temperatures and pressures the AC system must be working as designed. At this point it may be prudent to check that the customer is using the AC system properly.

Cooling off your vehicle interior as quickly as possible requires a scientific approach with your climate control system. Before getting to the control system improve your chances of getting cool fast by parking your vehicle in the shade when possible and leave the windows cracked open.

When you get in the vehicle it will likely be way hotter than the outside air. Open all the windows and start the engine and turn on the AC.

Do not select Max AC or the recirculating air mode. This requires that the AC system cools the interior air. Instead use regular AC mode that brings outside air in to cool. Once the interior of the vehicle is close to the outside temperature it is time to roll up the windows.

If you are going to be idling a lot and doing city driving use Max AC mode and recirculating air. Cooling down the interior will happen more quickly by recirculating the interior air through the air conditioner evaporator.

If you are going out on the highway and driving at speed turn off the recirculation mode and let in fresh air from outside to cool. The cooling capability of the AC system is increased when the vehicle is moving quickly through the air. Cooled fresh air is more comfortable than cooled recirculated air.

Be patient. Keep your cool.

Trail’s Ron Nutini is a licensed automotive technician and graduate of mechanical engineering from UBC. E-mail: nutechauto@telus.net

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