Having learned to drive in an era before air conditioning was standard, I still have vivid memories of motoring in hot, steamy climates. It was not fun.

By the 1970s when most cars had A/C, macho truckers refused it. One told me, “Air conditioning is for wimpy four-wheelers.” His decision to stay warm may have had more to do with cost and reliability, not his manhood.

Today, fleet managers know that proper cab climate control contributes to vehicle safety and driver health. A comfortable operator is a safe and efficient driver. Properly maintained A/C is as necessary for good vision in bad weather as it is for driver comfort. Even in winter, the A/C unit comes on with defrosters to help defrost cold windshields.

That's because A/C systems also perform another function: They remove moisture. During rain or snowstorms relative humidity is often close to 100%. By cooling air, the absolute amount of moisture is reduced because colder air cannot hold as much for a given volume.

In the last few years, manufacturers have toughened cab climate control systems, yet they still can be delicate. They are made of soft materials that, if abused, could create problems that can stop an A/C system cold (pardon the pun).

The major components of any A/C system are the compressor, condenser, receiver-dryer, expansion valve, and the evaporator. They are connected primarily by soft metal tubing, usually aluminum and copper.

The engine drives the compressor through a drive belt. As it turns, the compressor draws a refrigerant fluid from the evaporator as a gas and forces it to a condenser where the gas liquefies. The liquid refrigerant then flows to a receiver-drier where any condensed moisture is removed.

The liquid refrigerant next flows through an expansion valve into an evaporator, where it “boils” to its gaseous state by drawing heat from cab air through the evaporator. The gaseous refrigerant then returns to the compressor.

Guide for help

The Technology and Maintenance Council (TMC) has published a comprehensive Recommended Practice on truck air conditioning. RP 418, “Heavy-Duty In-Cab R-134a Air Conditioning Systems,” describes system components and their function, preventive maintenance, service procedures, diagnostics, and repairs.

At each oil change, inspect the sight glass on the receiver-drier. If there are bubbles, there is a leak in the system and maintenance should be performed. The other obvious sign of a problem is that the A/C does not cool adequately.