Infiniti QX4 (R50). Manual — part 454
Refrigeration System
REFRIGERATION CYCLE
NBHA0010
Refrigerant Flow
NBHA0010S01
The refrigerant flows in the standard pattern, that is, through the compressor, the condenser, the liquid tank,
through the evaporator, and back to the compressor. The refrigerant evaporation through the evaporator coil
is controlled by an externally equalized expansion valve, located inside the evaporator case.
Freeze Protection
NBHA0010S02
Under normal operating conditions, when the A/C is switched on, the compressor runs continuously, and the
evaporator pressure, and therefore temperature, is controlled by the V-6 variable displacement compressor to
prevent freeze up.
Refrigerant System Protection
NBHA0010S03
Refrigerant Pressure Sensor
NBHA0010S0303
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 2,746 kPa (28 kg/cm
2
, 398 psi) or below about 177 kPa
(1.8 kg/cm
2
, 26 psi).
Pressure Relief Valve
NBHA0010S0302
The refrigerant system is also protected by a pressure relief valve, located in the rear head of the compres-
sor. When the pressure of refrigerant in the system increases to an abnormal level [more than 3,727 kPa (38
kg/cm
2
, 540 psi)], the release port on the pressure relief valve automatically opens and releases refrigerant
into the atmosphere.
RHA347H
DESCRIPTION
Refrigeration System
HA-14
V-6 Variable Displacement Compressor
GENERAL INFORMATION
=NBHA0086
1. The V-6 variable compressor differs from previous units. The vent temperatures of the V-6 variable com-
press do not drop too far below 5°C (41°F) when:
I
evaporator intake air temperature is less than 20°C (68°F)
I
engine is running at speeds less than 1,500 rpm.
This is because the V-6 compressor provides a means of “capacity” control.
2. The V-6 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.
3. A “clanking” sound may occasionally be heard during refrigerant charge. The sound indicates that the tilt
angle of the swash plate has changed and is not a problem.
4. For air conditioning systems with the V-6 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.
5. A constant range of suction pressure is maintained when engine speed is greater than a certain value. It
normally ranges from 147 to 177 kPa (1.5 to 1.8 kg/cm
2
, 21 to 26 psi) under varying conditions.
In previous compressors, however, suction pressure was reduced with increases in engine speed.
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DESCRIPTION
V-6 Variable Displacement Compressor
HA-15
DESCRIPTION
=NBHA0087
General
NBHA0087S01
The variable compressor is basically 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 can be continu-
ously changed from 14.5 to 184 cm
3
(0.885 to 11.228 cu in).
RHA037DD
DESCRIPTION
V-6 Variable Displacement Compressor (Cont’d)
HA-16
Operation
=NBHA0087S02
1. Operation Control Valve
NBHA0087S0201
Operation control valve is located in the suction port (low-pressure) side, and opens or closes in response to
changes in refrigerant suction pressure.
Operation of the valve controls the internal pressure of the crankcase.
The angle of the swash plate is controlled between the crankcase’s internal pressure and the piston cylinder
pressure.
2. Maximum Cooling
NBHA0087S0202
Refrigerant pressure on the low-pressure side increases with an increase in heat loads.
When this occurs, the control valve’s bellows compress to open the low-pressure side valve and close the
high-pressure side valve.
This causes the following pressure changes:
I
the crankcase’s internal pressure to equal the pressure on the low-pressure side;
I
the cylinder’s internal pressure to be greater than the crankcase’s internal pressure.
Under this condition, the swash plate is set to the maximum stroke position.
RHA473C
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DESCRIPTION
V-6 Variable Displacement Compressor (Cont’d)
HA-17
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