Specifications

A/C System Components
3-23
TOYOTA Air Conditioning and Climate Control – Course 752
• Refrigerant Pressure Switch. This switch normally monitors refrigerant
p
ressure in the high-pressure side of the system (between the
compressor and the expansion valve). If the pressure is too high or
too low, the pressure switch opens to stop the compressor (via the
compressor clutch). A mid-pressure setting on many cars also controls
the high speed operation of the electric condenser fans.
• Normally Open Relays control the condenser fan(s) when the
thermo-switch and pressure switches are closed. However, when either
switch opens (sensing excessive pressure or temperature), the relays
are connected in the circuit to energize the fans. The wiring diagram
on the previous page shows a typical system that uses two fans that
may rotate at different speeds. With this circuit, three relays are used
to connect each fan to power or ground. This means that the two fans
can each be connected to power and ground for high speed operation
(parallel circuits) or they can be connected in series so each fan sees
about half of battery voltage (about 6 volts) for low speed operation.
•
In the circuit, if either sensor shows high resistance (caused by a loose
wire or corroded terminal) the
fans will always run at high speed.
A fail-safe circuit in the cooling fan ECU protects the system in case of a
component failure.
A multispeed fan motor in the air conditioning ductwork circulates cabin
(interior) air or fresh exterior air through the evaporator. In early Toyota
vehicles, a multi-position switch and resistor assembly in the circuit
changes the source voltage to the fan motor. The resistor block contains
multiple outlet terminals to introduce different resistance values into the
circuit to create the multiple speeds. At its highest speed, a full 12 volts
is supplied to the blower motor. To reduce blower speed, the switch
introduces a different resistance to create each of the lower blower speeds.
In current Toyota vehicles, the blower speed is controlled electronically
by the A/C controller.
A/C Blower
Motor
Fan Motor
12V
M
Resistor Block
Blower Switch
Lo
Hi
Resistor-Type
Blower Switch
Current passes through
some or all portions
of resistor depending on
blower switch speed
position.
Fig. 3-26
752f326
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