General
The refrigerant flows in the standard pattern, that is, through the compressor, the condenser, the receiver drier, through the evaporator, and back to the compressor.
The refrigerant flow through the evaporator coil is controlled by an externally equalized expansion valve, located inside the evaporator case.
The compressor repeats on and off to maintain the evaporator temperature within a specified range. When the evaporator coil temperature falls below a specified point, the thermo control amplifier interrupts the compressor operation. When the evaporator coil temperature rises above the specification, the thermo control amplifier allows compressor operation.
The refrigerant system is protected against excessively high or low pressures by the dual switch, located on the receiver drier. If the system pressure rises above, or falls below the specifications, the dual switch opens to interrupt compressor operation.
Air Conditioning Cycle (Refrigerant Flow). Scheme 124
The vane rotary type compressor has five vanes fitted in the rotor mounted on the shaft. The centrifugal force produced by rotation of the rotor in the elliptical cylinder causes the vanes to move out and change the volumes in the areas surrounded by the rotor and cylinder. Suction, compression and discharge take place 10 times per rotation. A roll type valve is used on the discharge side only. Shaft seals are provided for the shaft and front head to maintain air tightness in the compressor. A trigger valve is provided in the side block to apply a back pressure to the vanes. The compressor is charged with the specified quantity of compressor oil which is forced to all the parts for lubrication by the discharge pressure of the refrigerant.
Identifying A/C Compressor Components. Scheme 125
Rotation of the shaft changes the volumes in the areas surrounded by the rotor, vanes, cylinder and side block, thereby accomplishing the functions of suction, compression and discharge.
Scheme 126
Scheme 127
Scheme 128
- Suction: The low-pressure gaseous refrigerant forced out from the evaporator by rotation of the compressor passes from the suction side of the rear head through the check valve and enters the low pressure chamber in the rear head. The gaseous refrigerant is drawn into the cylinder by rotation of the vanes from the two suction ports provided in the side block. Air tightness in the cylinder chamber is maintained by the compressor oil. (Scheme 126): Identifying A/C Compressor Function
- Compression: Further rotation after suction makes the cylinder chamber smaller, thus the compression starts. (Scheme 127): Identifying Compression Function
- Discharge: When the refrigerant pressure in the cylinder chamber exceeds the high pressure value, the roll valve opens to discharge the refrigerant through the pipe portion jointly provided in the front side block into the high pressure chamber in the front head. The gaseous refrigerant in the high pressure chamber is led through a baffle to separate the compressor oil contained in the gaseous refrigerant before it is forced to the high pressure piping. (Scheme 128): Identifying Discharge Function
Trigger Valve
This mechanism is designed to maintain proper vane back pressure to allow the vanes to move out with ease when the compressor starts. The trigger valve is provided in the side block, and a ditch called the K-ditch is provided in the side block rotor surface. The trigger valve has a ball combined with a spring. When vane chattering readily occurs like when the compressor starts or when the difference between the high and low pressures is small, spring action causes the valve to open to provide additional back pressure to the vanes, thereby assuring smooth operation.
Identifying Trigger Valve Components. Scheme 129
Scheme 130
Scheme 131
- When compressor starts or when load is low: When the compressor starts or when the load is low (the high pressure value is low), the trigger valve is opened by spring action to apply the pressure of the high pressure chamber to the back plane of vane to prevent vane chattering. (Scheme 130): Operation (When Compressor Starts Or When Load Is Low)
- When compressor is in regular operation: When the pressure in the high pressure chamber of the compressor increases, the pressure difference closes the trigger valve against spring action. The oil port pressure of the side block is applied to the back plane of vane to maintain proper back pressure. (Scheme 131): Operation (When Compressor Is In Regular Operation)
Check Valve
A plate and spring are provided on the suction side of the rear head. When there is a large difference between the high and low pressures immediately after the compressor has stopped, reverse rotation of the compressor could cause counter flow to the evaporator, as no suction valve is provided. For this reason, a check valve is provided to prevent counter flow. Immediately after the compressor has stopped, the high pressure refrigerant forces the check valve up to close the suction side piping passage and prevent counter flow from the high to low pressure side.
Identifying Check Valve Components. Scheme 132
DUAL SWITCH
The dual switch is located on the high pressure line above the receiver drier. When an abnormal pressure occurs in the high pressure line, the dual switch is forced to OFF to stop operation of the compressor.
Scheme 133
- When the pressure is abnormally low [177 kPa (1.8 kg/cm 2, 26 psi) or less] The dual switch is forced to OFF to prevent operation of the compressor when there is no gas caused by leakage of the refrigerant.
- When the pressure is abnormally high [2,940 kPa (30 kg/cm 2, 427 psi) or more] The dual switch is forced to OFF to protect the air-conditioning cycle parts. (Scheme 133): Identifying Dual Switch Specifications
COMPRESSOR CLUTCH "ON" DELAY SYSTEM
When air conditioning system relay operates, a signal is entered into engine control module. Engine control module then judges engine operation and activates A/C relay. Maximum clutch "ON" delay occurs 0.8 seconds after A/C relay activates.
Identifying Compressor Clutch "ON" Delay System Function. Scheme 134
- When the A/C switch and fan switch are turned ON, the A/C relay activates. The compressor is turned on, and then the main and sub fans also operate. Blower relay operates to direct the air flow rate determined by FAN switch position.
- The thermo amplifier activates to stop the compressor clutch and main and sub fans.
- When the "High-Low" pressure switch operates, the compressor clutch is stop and the main and sub fans are stop.
Thermo Control Amplifier
The thermo control amplifier disconnects the magnet clutch circuit to prevent the evaporator from becoming frosted when the temperature of the evaporator fin drops close to "30°C (37°F)". As the evaporator is cooled, the thermistor (located on the evaporator fin) interrupts the "base" current of the amplifier. This in turn de-energizes the A/C relay coil, which in turn disconnects the magnet clutch circuit.
Identifying Thermo Control Amplifier Function. Scheme 135
Acceleration Cut System
The A/C switch turns the A/C system on or off. The on-off operation of the switch is transmitted to the ECM.
The A/C relay breaks the current flow to the compressor, through the use of an output signal from the ECM, for a certain period of time when a "full-throttle" signal (emitted from the throttle sensor) enters the ECM while the compressor is operating. This prevents the degradation of acceleration performance and stabilizes the main fuse box located on the left side of the engine compartment.
Identifying Acceleration Cut System Function. Scheme 136
I.S.C.
The I.S.C. (Idle Speed Control) increases engine idle speed when the compressor is turned ON.
The Engine Control module activates the idle speed control solenoid valve in advance to control the amount of by-pass air flowing through the throttle body in relation to the signal emitted from the A/C switch, so that the proper idle speed specified for each engine load is achieved.
A/C Request For Change In Idle Speed. Scheme 137
Fan Control
The main fan and sub fan are switch turn ON and OFF, according to the operating modes shown in the following table.
