What does it mean?
The air conditioning system keeps you cool in the summer and keeps your windows fog-free year-round. The air conditioning system can simply be described as a heat pump, removing heat from inside the vehicle and transferring it outside the vehicle, using a system of fans, radiators, and a compressor. The key to this heat-pumping capability is the refrigerant, typically R-134a, which circulates throughout the system via a series of tubes and hoses.
The compressor charges the high side of the system, as far as the expansion valve, where the refrigerant rapidly expands, vaporizing and absorbing heat in the evaporator, which is inside the passenger compartment. The heated refrigerant, on the low side of the system now, travels to the condenser, outside the passenger compartment, where it releases that heat to the atmosphere, and then returns to the compressor, continuing the cycle.
The high side and low sides of the system are separated by the compressor and the expansion valve. Under normal operation, refrigerant pressure usually ranges from 190 psi to 240 psi, on the high side, and 20 psi to 35 psi, on the low side, depending on system design, atmospheric conditions, and driver demand. The engine control module (ECM) monitors one or more refrigerant pressure sensors to cycle the belt-driven air conditioning compressor clutch and gauge system performance.
In case the ECM detects that refrigerant pressure is too low or too high, it will lock out air conditioner function to protect the compressor and the rest of the system from damage. Based on the voltage from the refrigerant pressure sensor, in case the ECM calculates it abnormally high, typically over 350 psi, it will lock out the compressor clutch and store a diagnostic trouble code (DTC) in memory, DTC P0533, “A/C Refrigerant Pressure Sensor Circuit High Input.”