Opel Frontera UE. Manual - part 1228

HEATING, VENTILATION AND AIR CONDITIONING (HVAC)

1A–33

Air Conditioning System

General Description

Air Conditioning Refrigerant Cycle Construction

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The refrigeration cycle includes the following four
processes as the refrigerant changes repeatedly from
liquid to gas and back to liquid while circulating.

Evaporation

The refrigerant is changed from a liquid to a gas inside

Legend

(1) Electronic Thermostat
(2) Evaporator Core
(3) Evaporator Assembly
(4) Temperature Sensor
(5) Blower Motor
(6) Expansion Valve
(7) Pressure Switch or Pressure Sensor
(8) Receiver/Drier

(9) Condenser

(10) Compressor
(11) Magnetic Clutch
(12) Mode (HEAT) Control Door
(13) Temp. Control Door (Air Mix Door)
(14) Heater Core
(15) Mode (VENT) Control Door
(16) Heater Unit
(17) Mode (DEF) Control Door

SECTION

1A–34

HEATING, VENTILATION AND AIR CONDITIONING (HVAC)

the evaporator.  The refrigerant mist that enters the
evaporator vaporizes readily. The liquid refrigerant
removes the required quantity of heat (latent heat of
vaporization) from the air around the evaporator core
cooling fins and rapidly vaporizes.  Removing the heat
cools the air, which is then radiated from the fins and
lowers the temperature of the air inside the vehicle.
The refrigerant liquid sent from the expansion valve and
the vaporized refrigerant gas are both present inside the
evaporator as the liquid is converted to gas.
With this change from liquid to gas, the pressure inside
the evaporator must be kept low enough for vaporization
to occur at a lower temperature.  Because of that, the
vaporized refrigerant is sucked into the compressor.

Compression

The refrigerant is compressed by the compressor until it
is easily liquefied at normal temperature.
The vaporized refrigerant in the evaporator is sucked
into the compressor.  This action maintains the
refrigerant inside the evaporator at a low pressure so
that it can easily vaporize, even at low temperatures
close to 0

°

C (32

°Φ).

Also, the refrigerant sucked into the compressor is
compressed inside the cylinder to increase the pressure
and temperature to values such that the refrigerant can
easily liquefy at normal ambient temperatures.

Condensation

The refrigerant inside the condenser is cooled by the
outside air and changes from gas to liquid.
The high temperature, high pressure gas coming from
the compressor is cooled and liquefied by the
condenser with outside air and accumulated in the
receiver/drier. The heat radiated to the outside air by the
high temperature, high pressure gas in the compressor
is called heat of condensation. This is the total quantity
of heat (heat of vaporization) the refrigerant removes
from the vehicle interior via the evaporator and the work
(calculated as the quantity of heat) performed for
compression.

Expansion

The expansion valve lowers the pressure of the
refrigerant liquid so that it can easily vaporize.
The process of lowering the pressure to encourage
vaporization before the liquefied refrigerant is sent to
the evaporator is called expansion. In addition, the
expansion valve controls the flow rate of the refrigerant
liquid while decreasing the pressure.
That is, the quantity of refrigerant liquid vaporized inside
the evaporator is determined by the quantity of heat
which must be removed at a prescribed vaporization
temperature. It is important that the quantity of
refrigerant be controlled to exactly the right value.

Compressor

The compressor performs two main functions:
It compresses low-pressure and low-temperature
refrigerant vapor from the evaporator into high-pressure
and high-temperature refrigerant vapor to the
condenser.
It pumps refrigerant and refrigerant oil through the air
conditioning system.
This vehicle is equipped with a five-vane rotary
compressor.
The specified amount of the compressor oil is 150cc
(5.0fl.oz.).
The oil used in the HFC-134a system compressor
differs from that used in R-12 systems.
Also, compressor oil to be used varies according to the
compressor model.  Be sure to avoid mixing two or more
different types of oil.
If the wrong oil is used, lubrication will be poor and the
compressor will seize or malfunction.
The magnetic clutch connector is a waterproof type.

Magnetic Clutch

The compressor is driven by the drive belt from the
crank pulley of the engine. If the compressor is activated
each time the engine is started, this causes too much
load to the engine. The magnetic clutch transmits the
power from the engine to the compressor and activates
it when the air conditioning is ON. Also, it cuts off the
power from the engine to the compressor when the air
conditioning is OFF. Refer to Compressor in this section
for magnetic clutch repair procedure.

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Legend

(1) Magnetic Clutch
(2) Magnetic Clutch Harness Connector
(3) Compressor

SECTION

HEATING, VENTILATION AND AIR CONDITIONING (HVAC)

1A–35

Condenser

The condenser assembly is located in front of the
radiator. It provides rapid heat transfer from the
refrigerant to the cooling fins.
Also, it functions to cool and liquefy the high-pressure
and high-temperature vapor sent from the compressor
by the radiator fan or outside air.
A condenser may malfunction in two ways: it may leak,
or it may be restricted.  A condenser restriction will
result in excessive compressor discharge pressure.  If a
partial restriction is present, the refrigerant expands
after passing through the restriction.
Thus, ice or frost may form immediately after the
restriction. If air flow through the condenser or radiator
is blocked, high discharge pressures will result. During
normal condenser operation, the refrigerant outlet line
will be slightly cooler than the inlet line.
The vehicle is equipped with the parallel flow type
condenser. A larger thermal transmission area on the
inner surface of the tube allows the radiant heat to
increase and the ventilation resistance to decrease.
The refrigerant line connection has a bolt at the block
joint, for easy servicing.

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Receiver / Drier

The receiver/drier performs four functions:

• As the quantity of refrigerant circulated varies

depending on the refrigeration cycle conditions,
sufficient refrigerant is stored for the refrigeration
cycle to operate smoothly in accordance with
fluctuations in the quantity circulated.

• The liquefied refrigerant from the condenser is mixed

with refrigerant gas containing air bubbles. If
refrigerant containing air bubbles. If refrigerant
containing air bubbles is sent to the expansion valve,
the cooling capacity will decrease considerably.
Therefore, the liquid and air bubbles are separated
and only the liquid is sent to the expansion valve.

• The receiver/drier utilizes a filter and drier to remove

the dirt and water mixed in the cycling refrigerant.

• The sight glass, installed atop the receiver/drier,

show the state of the refrigerant.

A receiver/drier may fail due to a restriction inside the
body of the unit. A restriction at the inlet to the receiver/
drier will cause high pressure.
Outlet restrictions will be indicated by low pressure and
little or no cooling. An excessively cold receiver/drier
outlet may indicate a restriction.
The receiver/drier of this vehicle is made of aluminum
with a smaller tank. It has a 300cc refrigerant capacity.
The refrigerant line connection has a bolt at the block
joint, for easy servicing.

Dual Pressure Switch (V6,M/T)

The pressure switch (Dual pressure switch) is installed
on the upper part of the receiver/drier, to detect
excessively high pressure (high pressure switch) and
prevent compressor seizure due to the refrigerant
leaking (low pressure switch), so that the compressor is
able to be turned “ON" or “OFF".

Triple Pressure Switch (V6, A/T)

Triple pressure switch is installed on the upper part of
the receiver/drier. This switch is constructed with a
unitized type of two switches. One of them is a low and
high pressure switch (Dual pressure switch) to switch
“ON" or “OFF" the magnetic clutch as a result of
irregularly high-pressure or low pressure of the
refrigerant. The other one is a medium pressure switch
(Cycling switch) to switch “ON" or “OFF" the condenser
fan sensing the condenser high side pressure.

Legend

(1) Pressure Switch
(2) Receiver/Drier
(3) Condenser & Receiver Tank Assembly
(4) Condenser Fan (6VD1 A/T)

Compressor

ON

(kPa/psi)

OFF

(kPa/psi)

Low-pressure 

control

186.3

±

29.4 

(27.0

±

4.3)

176.5

±

19.6 

(25.6

±

2.8)

High-pressure 

control

2350.4

±

196.1 

(340.7

±

28.4)

2942.0

±

196.1 

(426.6

±

28.4)

Compressor

ON

(kPa/psi)

OFF

(kPa/psi)

Low-pressure 

control

186.3

±

29.4 

(27.0

±

4.3)

176.5

±

24.5 

(25.6

±

3.6)

High-pressure 

control

2353.6

±

196.1 

(341.3

±

28.4)

2942.0

±

196.1 

(426.6

±

28.4)

SECTION

1A–36

HEATING, VENTILATION AND AIR CONDITIONING (HVAC)

Expansion Valve

This expansion valve is an external pressure type and it
is installed at the evaporator intake port.
The expansion valve converts the high pressure liquid
refrigerant sent from the receiver/drier to a low pressure
liquid refrigerant by forcing it through a tiny port before
sending it to the evaporator.
This type of expansion valve consists of a temperature
sensor, diaphragm, ball valve, ball seat, spring
adjustment screw, etc.
The temperature sensor contacts the evaporator outlet
pipe, and converts changes in temperature to pressure.
It then transmits these to the top chamber of the
diaphragm.
The refrigerant pressure is transmitted to the
diaphragm's bottom chamber through the external
equalizing pressure tube.
The ball valve is connected to the diaphragm. The
opening angle of the expansion valve is determined by
the force acting on the diaphragm and the spring
pressure.
The expansion valve regulates the flow rate of the
refrigerant. Accordingly, when a malfunction occurs to
this expansion valve, both discharge and suction
pressure get low, resulting in insufficient cooling
capacity of the evaporator.
The calibration has been changed to match the
characteristics of HFC-134a.

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Evaporator

The evaporator cools and dehumidifies the air before
the air enters the passenger compartment.
High-pressure liquid refrigerant flows through the
expansion valve into the low-pressure area of the
evaporator. The heat in the air passing through the
evaporator core is lost to the cooler surface of the core,
thereby cooling the air.
As heat is lost between the air and the evaporator core
surface, moisture in the vehicle condenses on the
outside surface of the evaporator core and is drained off
as water.
When the evaporator malfunctions, the trouble will show
up as an inadequate supply of cool air. The cause is
typically a partially plugged core due to dirt, or a
malfunctioning blower motor.
The evaporator core with a laminate louver fin is a
single-sided tank type where only one tank is provided
under the core.

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Electronic Thermostat (With Manual A/C)

The thermostat consists of the thermo sensor and
thermostat unit which functions electrically to reduce the
noises being generated while the system is in operation.
The electronic thermo sensor is mounted at the
evaporator core outlet and senses the surface
temperature of the evaporator core. Temperature
signals are input to the thermostat unit. This information
is compared by the thermo unit and results in the output
to operate the A/C thermostat relay and turn the
magnetic clutch ON or OFF to prevent evaporator
freeze-up.
A characteristic of the sensor is that the resistance

Condenser fan

ON

(kPa/psi)

OFF

(kPa/psi)

Medium-pressure 

control

1471.0

±

98.1 

(213.3

±

14.2)

1078.7

±

117.7 

(156.4

±

17.1)

Legend

(1) Expansion Valve
(2) Insulator
(3) Evaporator Assembly

Legend

(1) Evaporator Core
(2) Insulator
(3) Expansion Valve

SECTION