Refrigeration System

REFRIGERATION SYSTEM

Refrigerant Cycle

REFRIGERANT FLOW
The refrigerant flows from the compressor, through the condenser with liquid tank, through the evaporator, and back to the compressor. The refrigerant evaporation in the evaporator is controlled by an externally equalized expansion valve, located inside the evaporator case.

FREEZE PROTECTION
To prevent evaporator frozen up, the evaporator air temperature is monitored, and the voltage signal to the unified meter and A/C amp. will make the A/C relay go OFF and stop the compressor.

Refrigerant System Protection

REFRIGERANT PRESSURE SENSOR
The refrigerant system is protected against excessively high- or low-pressures by the refrigerant pressure sensor, located on the liquid tank. If the system pressure rises above, or falls below the specifications, the refrigerant pressure sensor detects the pressure inside the refrigerant line and sends the voltage signal to the ECM. ECM makes the A/C relay go OFF and stops the compressor when pressure on the high-pressure side detected by refrigerant pressure sensor is over about 3,119 kPa (31.8 kg/sq.cm, 452 psi), or below about 118 kPa (1.2 kg/sq.cm, 17 psi).




PRESSURE RELIEF VALVE
The refrigerant system is also protected by a pressure relief valve, located in the rear head of the compressor. When the pressure of refrigerant in the system increases to an unusual level [more than 3,628 kPa (37 kg/sq.cm, 526 psi)], the release port on the pressure relief valve automatically opens and releases refrigerant into the atmosphere.

Variable Displacement Compressor

GENERAL INFORMATION
1. The variable compressor provides refrigerant control under varying conditions. During cold winters, it may not produce high refrigerant pressure discharge (compared to previous units) when used with air conditioning systems.
2. For air conditioning systems with the compressor, the clutch remains engaged unless: the system main switch, fan switch or ignition switch is turned OFF. When ambient (outside) temperatures are low or when the amount of refrigerant is insufficient, the clutch is disengaged to protect the compressor.

DESCRIPTION




General
The variable compressor is a swash plate type that changes piston stroke in response to the required cooling capacity.
The tilt of the swash plate allows the piston's stroke to change so that refrigerant discharge continuously change from approx. 0 to 171 cu.cm (0 to 10.4 cu in).

Operation
1. Control Valve
- By changing high-pressure valve lift amount, built-in electronic control valve executes the following:
- Controls high-pressure valve discharge amount.
- Changes crankcase pressure in compressor.
- Changes angle of swash plate.
- Amount of high-pressure valve lift is determined by factors below.
- Low-pressure applied to diaphragm
- Spring load of set spring
- Balance of magnetic force generated in magnet coil

- Electronic control valve (ECV) magnet coil receives electric signal (duty control) from unified meter and A/C amp. Then, magnetic force generated by electric current is changed to control high-pressure valve lift amount.




2. Maximum Cooling
High-pressure valve is closed by magnetic force generated by electric signal sent from unified meter and A/C amp. At this time, cylinder moves full stroke due to pressure balance between inside crankcase (Pc) and suction line (Ps).
Under this condition, the swash plate is set to the maximum stroke position.




3. Capacity Control
When no electric signal is sent from unified meter and A/C amp. (current: OFF), high-pressure valve is opened by spring force.
Since suction pressure is low, it makes the suction port close and the discharge port open. Thus, crankcase pressure becomes high as high-pressure enters the crankcase.

- The force acts around the link near the swash plate, and is generated by the pressure difference before and behind the piston.
- The thrust flange and link are located where the piston generates the highest pressure. Piston pressure is between suction pressure Ps and discharge pressure Pd, which is close to suction pressure Ps. If crankcase pressure Pc rises due to capacity control, the force around the link makes the swash plate angle decrease and also the piston stroke decrease. In other words, crankcase pressure increase triggers pressure difference between the piston and the crankcase. The pressure difference changes the angle of the swash plate.

Exploded View ATC-25:

Component Layout