There are two basic types of automotive air conditioning systems: one uses an expansion valve to remove pressure from the liquid refrigerant, while the other uses an orifice tube.
How an air conditioning system works
The compressor pumps low-temperature refrigerant gas and compresses it into a high-pressure, high-temperature gas. The refrigerant is sent to the condenser in front of the radiator, where the condenser removes some of the heat through the ambient air passing through its fins, causing the refrigerant to change from a hot gas to a hot liquid.
In an air conditioning system with an expansion valve, the hot liquid passes through a receiver-dryer, which removes moisture to maximize the efficiency of the refrigerant's heat exchange capacity. The refrigerant then passes through the expansion valve, which has a detection line connected to the A/C compressor inlet, allowing the pressure to be maintained.
In an orifice tube system, hot liquid refrigerant passes directly from the condenser to the orifice tube. The orifice tube system maintains pressure at the A/C compressor inlet by using a clutch to turn the compressor on and off. The expansion of the hot liquid through the expansion valve or orifice causes a pressure drop and therefore a temperature drop.
Air from the cabin then passes through one side of the coils to an evaporator, and the low-temperature liquid refrigerant passes through the other side. Heat is removed from the air in the cabin by the refrigerant and returned to the A/C compressor inlet as a low-temperature gas.
In the orifice tube system, an accumulator located between the evaporator and the A/C compressor inlet has a desiccant for moisture removal like the receiver-dryer used in the expansion valve system. However, it also collects unevaporated refrigerant to prevent compressor liquid blockage.
Common air conditioning problems and possible solutions
Symptom: Low compressor discharge pressure
Leak in system (repair), bad expansion valve (replace), suction valve closed (open), lack of freon (add freon), connected receiver dryer (replace dryer), leaky compressor suction valve (replace) , defective reed valves on the compressor (replace).
Symptom: High compressor discharge pressure
Air in system (charging system), clogged condenser (clean condenser), drain valve closed (open), system overloaded (remove some refrigerant), insufficient air from condenser (install large fan), loose fan belt (tighten ), condenser not centered fan or too far from radiator (center and control distance).
Symptom: Low suction pressure
Lack of refrigerant (add refrigerant), worn compressor piston (replace compressor), leaking compressor head gasket (replace head gasket), kinked or flattened hose (replace), leaking compressor inlet valve (replace the hose), moisture in the system (replace dryer), residue in the expansion valve or filter (replace dryer).
Symptom: High suction pressure
Loose expansion valve (tighten), overloaded system (remove some refrigerant), expansion valve stuck open (replace), faulty compressor reed valves (replace), leaking compressor head gasket (replace head gasket head) .
Symptom: compressor does not work
Broken belt (replace), broken clutch cable or lack of 12V power (repair or power control cable), broken compression piston (replace compressor), defective thermostat (replace), defective clutch coil (replace ), low coolant (add coolant).
