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But learning about the basics of A/C system operation can help technicians service every system with skill.

All Air Conditioning (A/C) systems are not created equal, given that some are designed to OE specifications while others are not. But learning about the basics of A/C system operation can help technicians service every system with skill.

A/C Systems – Understanding the Basics:

When two objects at different temperatures are placed next to each other, heat will flow from the warmer of the two to the cooler one. Heat transfer stops when both objects reach the same temperature. To cool vehicle interiors, the natural flow of heat is reversed with the heat removed and absorbed by refrigeration. By controlling the state of the refrigerant, the amount of heat absorbed and radiated to the atmosphere is also controlled.

Today's air conditioning systems employ four basic parts:

• A mechanical compressor, driven by the engine
  
• A restriction, which creates a pressure drop so low-pressure liquid can absorb heat from the passenger compartment
  
• Two heat exchangers – the evaporator and the condenser
  
• A refrigerant, which transfers heat from the passenger compartment to the external environment
  

The design of an A/C system is determined by the restriction used to create a pressure drop in the system. There are two styles of restrictions commonly used: the orifice tube and the thermostatic expansion valve. The restriction is critical, as it gives the compressor something to push or pump against, as well as controlling volume flow and metering the correct amount of refrigerant through the entire system.

When the compressor starts running, it pulls refrigerant from the evaporator coil and forces it into the condenser coil. Because of the restriction, low-pressure liquid is pulled from the evaporator. The restriction also allows refrigerant pushed by the compressor to the condenser to be compressed to a higher pressure. Refrigerant passes through the condenser on its way from the compressor to the expansion valve and then from the expansion valve to the evaporator. After passing through the evaporator tubing, the refrigerant is returned to the compressor through its inlet.

While there is a "high-side" and a "low-side" to an A/C system, a phase change occurs in each half of the system. In the "low-side," after the restriction and before the compressor, low-pressure liquid is vaporized as heat is absorbed from the passenger compartment. In the "high-side," after the compressor and before the restriction, high-pressure vapor condenses to a high-pressure liquid and is then exchanged into the atmosphere.

A/C System Diagnostics and Resources

When servicing an A/C system, the first and most important step is a visual check of system components. Look for refrigerant leaks, compressor clutch damage, plugged evaporator drain tubes, blocked condenser fins and corroded connections. Further diagnosis requires a good set of refrigerant pressure gauges, a leak detector and a multimeter for electrical diagnosis of switches, sensors and the A/C clutch coil.

A/C gauges will display both high- and low-side pressures. Deviations from the proper operating pressures indicate a problem in the system. Late-model systems and vehicles equipped with automatic temperature controls typically have on-board diagnostics. A scan tool can then be used to check for trouble codes.

Delphi's complete array of diagnostic tools and technical support for A/C systems includes the new hand-held AC Analyzer and the Delphi Compressor Turning Tool, which is compatible with Delphi H6-, R4-, V5- and V7-style compressors. In addition to compressors, Delphi offers a wide range of other OE-validated components including condensers, evaporators and blower motors – all of which provide OE-level fit and quality for superior results on any A/C system maintenance or repair job. Every Delphi A/C component is engineered with the same OE expertise Delphi uses to develop advanced Heating, Ventilation, and Air Conditioning (HVAC) Modules, which are integrated units designed to filter, condition and deliver air in support of vehicle interior comfort and convenience.