Refrigerant Circuit Layout And Function

The condenser and the receiver/dryer are on the high pressure side, and the receiver/dryer or the expansion valve serves as the separator between the high pressure side and the low pressure side.
High pressure results from the restrictor or expansion valve forming a constriction and causing the refrigerant to accumulate, thus leading to an increase in pressure and temperature.
Excess pressure is generated if too much refrigerant or refrigerant oil is added, the condenser is contaminated, the radiator fan is faulty, the system is blocked or if there is moisture in the refrigerant circuit (the restrictor or expansion valve freezes).
Located on the low pressure side are the evaporator, the evaporator temperature sensor and compressor to separate low pressure side (ND gas sides) and high pressure side (HD gas sides).
A drop in system pressure can be caused by loss of refrigerant, faulty or plugged restrictor or expansion valve (no constriction), a malfunctioning A/C compressor or an iced-up evaporator.