Refrigerant Circuit Layout And Function

The condenser, receiver/dryer and the restrictor or expansion valve to separate the high pressure side (HD liquid sides) and low pressure side (ND liquid sides) ends are located on the high 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 decrease in system pressure can be caused by refrigerant loss, a faulty or blocked expansion or restrictor valve (constrictions), a faulty A/C compressor, or an iced-up evaporator.