Infiniti FX35, FX50 (S51). Manual - part 1123

REFRIGERATION SYSTEM

HA-5

< SYSTEM DESCRIPTION >

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SYSTEM DESCRIPTION

REFRIGERATION SYSTEM

System Diagram

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System Description

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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 from freezing up, the evaporator air temperature is monitored, and the voltage signal to
the unified meter and A/C amp. makes 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 sen-
sor, located on the liquid tank. The refrigerant pressure sensor detects the pressure inside the refrigerant line
and sends the voltage signal to the ECM if the system pressure rises above, or falls below the specifications. 
The high-pressure side detected by refrigerant pressure sensor is approximately 3,120 kPa (31.8 kg/cm

2

, 452

psi) or more when the engine speed is 1500 rpm or more. It is approximately 2,740 kPa (27.9 kg/cm

2

, 397 psi)

when the engine speed is less than 1,500 rpm. When it is approximately 120 kPa (1.2 kg/cm

2

, 17 psi) or less,

ECM turns the A/C relay to OFF and stops the compressor.

Pressure Relief Valve

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

2

,

526 psi)].

RJIA1552E

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REFRIGERATION SYSTEM

Component Parts Location

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1.

Refrigerant pressure sensor

2.

Liquid tank

3.

Condenser

4.

Compressor

JSIIA1278ZZ

REFRIGERATION SYSTEM

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Component Description

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1.

Expansion valve

2.

Evaporator

3.

Blower motor

JSIIA1279ZZ

Component

Description

Compressor

Intakes, compresses, and discharges refrigerant, to circulate refrigerant inside the refrigerant cycle.

Condenser

Cools refrigerant discharged from compressor, and transforms it to liquid refrigerant.

Liquid tank

Eliminates foreign matter in refrigerant, and stores temporarily liquid refrigerant.

Refrigerant pressure sensor

Refer to 

EC-494, "Description"

.

Expansion valve

Transforms high-pressure liquid refrigerant to mist form low-pressure liquid refrigerant by drawing 
function.

Evaporator

The mist form liquid refrigerant transforms to gas by evaporation by the air conveyed from blower 
motor. The air is cooled by the heat by evaporation.

Blower motor

Takes in air in the vehicle or fresh outside air, provides it forcedly to the air conditioner, and conveys 
it inside the vehicle.

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REFRIGERATION SYSTEM SYMPTOMS

SYMPTOM DIAGNOSIS

REFRIGERATION SYSTEM SYMPTOMS

Trouble Diagnosis For Unusual Pressure

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Diagnose using a manifold gauge whenever system’s high and/or low side pressure(s) is/are unusual. The
marker above the gauge scale in the following tables indicates the standard (usual) pressure range. Refer to
above table (Ambient air temperature-to-operating pressure table) since the standard (usual) pressure, how-
ever, differs from vehicle to vehicle.

Symptom Table

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Gauge indication

Refrigerant cycle

Probable cause

Corrective action

Both high- and low-pressure sides 
are too high.

The pressure returns to nor-
mal is reduced soon after wa-
ter is splashed on condenser.

Excessive refrigerant charge in 
refrigeration cycle.

Reduce refrigerant until speci-
fied pressure is obtained.

Air suction by cooling fan is in-
sufficient.

Insufficient condenser cooling 
performance.

↓

1.

Condenser fins are 
clogged.

2.

Improper fan rotation of 
cooling fan.

• Clean condenser.
• Check and repair cooling fan 

if necessary.

• Low-pressure pipe is not 

cold.

• When compressor is 

stopped, high-pressure 
reading quickly drops by 
approximately 196 kPa (2 

kg/cm

2

, 28 psi). It then de-

creases gradually thereaf-
ter.

Poor heat exchange in con-
denser
(After compressor operation 
stops, high-pressure decreas-
es too slowly).

↓

Air in refrigeration cycle.

Evacuate repeatedly and re-
charge system.

Engine tends to overheat.

Engine cooling systems mal-
function.

Check and repair each engine 
cooling system.

• An area of the low-pressure 

pipe is colder than areas 
near the evaporator outlet.

• Low-pressure pipe is some-

times covered with frost.

• Excessive liquid refrigerant 

on low-pressure side.

• Excessive refrigerant dis-

charge flow.

• Expansion valve is open a lit-

tle compared with the speci-
fication.

↓

Improper expansion valve ad-
justment.

Replace expansion valve.

High-pressure side is too high and 
low-pressure side is too low.

Upper side of condenser and 
high-pressure side are hot, 
however, liquid tank is not so 
hot.

High-pressure tube or parts lo-
cated between compressor 
and condenser are clogged or 
crushed.

• Check and repair or replace 

malfunctioning parts.

• Check lubricant for contami-

nation.

AC359A

AC360A