Specifications

Section 3
3-18
TOYOTA Technical Training
Lines and
Hoses
There may be one or more pressure switches in the refrigerant lines.
C
urrent models use a M
ultipressure Switch
t
hat contains two or even
three pressure-sensing circuits. It is located in the high-pressure line of
the system (between the compressor and expansion valve).
• Low pressure – The low-pressure sensing circuit switches the compressor
OFF. This prevents system damage due to the reduced amount of
lubricant as a result of low system pressure. An external leak will also
be detected by this sensing circuit.
• Medium pressure – The A/C control unit monitors pressures within
this range to contr
ol the operation of the high-speed condenser fan.
•
High pressure – Excessively high system pressure indicates a malfunction.
This sensing circuit switches OFF the compressor clutch to prevent
system damage.
The term “psig” indicates gauge pressure that takes into consideration
atmospheric pressure of 14.5 pounds per square inch and displays it as “0”
on a pressure gauge.
During normal operation, the amplifier cycles the compressor clutch
ON and OFF to maintain an evaporator temperature of approximately
32° F (0° C). When the amplifier detects a malfunction in the system, it
will de-energize the compressor clutch and flash the A/C signal lamp.
A Diagnostic Trouble Code will generate and will stay in memory until
the ignition switches OFF.
Refrigerant flows through the system in rigid metal lines and flexible
rubber hoses. Connections at each component and between lines provide
convenient installation in the vehicle as well as to service and repair
system components. Since the high-pr
essure side contains a high-pres-
sur
e liquid, it uses much smaller diameter lines than the low side, and
being a closed system, the volume of refrigerant is always the same at any
point in the system. Only the pressure and the physical state of the
Multipressure
Switch
Note:
Compressor
Clutch
Condenser Fan
(High Speed)
Source Voltage Source Voltage
Magnetic Clutch Control
Low
Pressure
(NC)
Medium
Pressure
(NC)
High
Pressure
(NC)
Multipressure
Switch
4 Pins
3 Pressures
Fig. 3-19
752f319
Fig. 3-20
752f320
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