Using Your Air Conditioner in Winter

Light & Medium Truck, Oct 2007

You may not realize it, but your air conditioner has a big effect on whether your truck's defroster is working at peak efficiency.

The air conditioner removes excess moisture from the air, which helps the defroster clear the wiper-stroke area and the door window glass.

"If there's one thing you can do to improve the performance of your defroster and to increase your margin of safety on the highway, it's to have your air conditioner inspected at the start of the heating season," said Gary Hansen, vice president of engineering for Red Dot Corp. Based in Seattle, Red Dot designs and manufactures heating and air-conditioning systems, components and replacement parts for heavy trucks and other commercial vehicles.

There are other steps to prepare a truck for cooler temperatures, Hansen said. Most are quick, simple and inexpensive.

* Ducts: Turn on the defroster and run a hand under the dash, feeling for air leaks. Fill holes in the ducts with a compound or tape designed for heating systems.

* Filters: The heating, ventilation and air conditioning system has at least one pleated paper or foam filter to capture dust, lint, carpet fibers and other impurities that can clog the heat exchangers and reduce the efficiency of the heater system. Depending on the truck model, there will be one filter on the fresh-air inlet and another for recirculated air.

"Dirty filters can restrict air flow and allow dirt and dust to interfere with the evaporator core," Hansen said. Most truck manufacturers recommend checking the filter every three months and replacing it with a filter that meets the original-equipment spec.

* Valves: Check the heater's water valves to make sure they open and close completely and that the actuator cables aren't stretched. Remind drivers that valves may be sticky after a season of disuse. "If the driver tries to force the valve to open or close, he risks stretching the cable and damaging the valve," Hansen said.

* Blower motors: They get a workout in the winter. "On a cold morning, the motor goes from zero to full-speed in one swift turn of the knob," Hansen said. "The motor should take no more than 30 minutes to remove and replace, so do it at the first sign of trouble."

* Receiver-drier: It contains desiccant, a chemical that attracts and traps moisture. When desiccant becomes saturated, moisture in the system is free to combine with refrigerant and turn into corrosive hydrofluoric acid. The receiver-drier should be replaced once a year, and the sight glass on the moisture indicator should be checked during an oil change or any scheduled maintenance procedure. A blue dot means the refrigerant is dry; pink, white or gray indicates acid or moisture in the system.

"It may seem odd that the air conditioner is so critical in cold weather," Hansen said, "but it reinforces the need to see a qualified A/C service technician at regular intervals during the year, not just during hot weather."

- Red Dot Corp.