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Recharging an AC System

Once considered a luxury, air conditioning in machinery is now a necessity, demanding the same maintenance management as an engine or transmission. In the case of air conditioning, the equipment at work consists of a compressor, hoses, evaporator in the cab, a condenser in front of the radiator, system drier, flow valves, and a refrigerant (R-12, R-134a). Mixed in with the refrigerant is a special oil that keeps the moving parts in the compressor lubricated.

Any system also has two refrigerant pressure pathways: low side and high side. The low side (using larger hoses) has the refrigerant in a gaseous state. On the high side, it’s in a liquid state.

There are Schrader valve ports on both the low side and the high side. They are used to check pressure and to service.

Typical service is to keep the condenser free of debris, change the cabin filter, and maintain drive-belt tension. For longer lasting results, try a higher level of service.

A higher level of maintenance
System operating pressure is directly linked to the thermal load in cab temperature. It is also linked – and more importantly – to the ambient and under-hood temperature of the equipment. A hardworking engine operating on a hot day will significantly raise the high-side pressure.

For this reason, there is usually a safety blow-off valve integrated into the design. A properly maintained and operating system will never evoke the blow-off valve.

System pressure is constantly going up and down, depending on thermal load and engine rpm. When hoses age or are oil-soaked from an engine leak, they become porous. When the system pressure reaches a certain level, the refrigerant then starts to leak through the hose and into the atmosphere. The result is poor performance due to a lack of refrigerant but no visible sign of a leak. Keeping the engine clean goes a long way in preventing hose failure.

The system also employs many rubber-type O-ring seals that, over time, will leak slightly. If the machine is many years old, it will inherently lose some refrigerant, even though nothing is wrong.

When this occurs, moisture is introduced into the system and mixes with the refrigerant and creates acid. This, in turn, deteriorates all of the internal components.

Every few years the system is meant to be discharged (refrigerant removed), evacuated (a vacuum is introduced in the system to boil off moisture), and then refilled with fresh refrigerant and oil.

This job requires a dedicated tool that is costly. So it’s best to schedule this maintenance with your dealer.

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