Maintenance is needed if wet floor mats indicate a clogged drain; vibration or unusual noise indicates debris; the vehicle has been out of service for a while; animals build nests in the blower fan; air flow is reduced from ice buildup on the evaporator; or a musty, mildew odor indicates mold growth in the evaporator box.

I mentioned that A/C units are delicate due to their relatively soft materials. With proper care, they will withstand a lifetime of use, but a little abuse can lead to costly repairs. Remind your service team not to allow heavy tools to contact tubing or fins in either heat exchanger (condenser or evaporator). By just laying a tool against them, the mechanic can cause a dent or rupture, especially if the unit is still under pressure.

Also, remind mechanics to use a solid (non-ratcheting) wrench on both sides of the fitting when tightening refrigerant lines. Avoid any excess torque on the tubing. Tube or line wrenches are best for tightening or loosening flare nut fittings.

Finding leaks

When performing maintenance, use proper equipment and follow procedures to evacuate and capture any refrigerant in the system. It is no longer enough to simply add a can or two of R-134a to the air conditioner. You are required to use leak-detecting dye to determine why refrigerant is low and correct any leaks. There are steep fines for failing to do so.

Never discharge an A/C system to the atmosphere by loosening a fitting or removing a service valve. Mechanics risk large fines, and can lose licenses and accreditation if they do so.

For many years, DuPont's Freon, also called R-12, was the standard refrigerant in vehicles. In the early 1980s, R-12 was found to attack the earth's protective ozone layer. R-12 was phased out in favor of R-134a, the standard today. Be sure to use only this new refrigerant.

Finally, create a job safety analysis program that requires the proper protective gear when working on air conditioning. Goggles or other eye protection and work gloves designed for cold temperatures are critical.

A rapidly discharging component or refrigerant can draw a great deal of heat in seconds. If a mechanic's skin is in contact, frostbite could develop. Soak the area in cold water, then call 911 immediately.

Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Associations and is currently on the Board of Truck Writers of North America.

Best Practices

The ATA Technology & Maintenance Council (TMC) is a diverse group of professionals who work to improve truck equipment and technology. TMC develops recommended practices for fleet managers to efficiently specify and maintain vehicles.