Corolla S Sedan L4-1794cc 1.8L DOHC MFI (2001)
Radiator Cooling Fan Motor: Description and Operation
Radiator Fan and Air Conditioning
SYSTEM OUTLINE
1. HEATER BLOWER MOTOR OPERATION
The current is applied at all times through the FL ALT fuse to the HTR fuse to TERMINAL 1 of the HTR relay.
When the ignition SW is turned on, the current flows through the GAUGE fuse to TERMINAL 5 of the HTR relay to coil to TERMINAL 3 to
TERMINAL 3 of the blower SW.
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Low speed operation
When the blower SW is moved to LO position, the current flows to TERMINAL 3 of the blower SW to TERMINAL 1 to GROUND, turning
the HTR relay on. This causes the current to flow from the HTR fuse to TERMINAL 1 of the HTR relay to TERMINAL 2 to TERMINAL 1 of
the blower motor to TERMINAL 2 to TERMINAL 4 of the blower resistor to TERMINAL 1 to GROUND, rotating the blower motor at low
speed.
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Medium speed operation (Operation at M1, M2)
When the blower SW is moved to M1 position, the current flows to TERMINAL 3 of the blower SW to TERMINAL 1 to GROUND, turning
the HTR relay on. This causes the current to flow from the HTR fuse to TERMINAL 1 of the HTR relay to TERMINAL 2 to TERMINAL 1 of
the blower motor to TERMINAL 2 to TERMINAL 4 of the blower resistor to TERMINAL 3 to TERMINAL 4 of the blower SW to
TERMINAL 1 to GROUND. At this time, the blower resistance of the blower resistor is less than at low speed, so the blower motor rotates at
medium low speed.
When the blower SW is moved to M2 position, the current through the motor flows from TERMINAL 4 of the blower resistor to TERMINAL
2 to TERMINAL 8 of the blower SW to TERMINAL 1 to GROUND. At this time, resistance of the blower resistor is less than at M1 position,
so the blower motor rotates at medium high speed.
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High speed operation
When the blower SW is moved to HI position, the current flows to TERMINAL 3 of the blower SW to TERMINAL 1 to GROUND, turning
the HTR relay on.
This causes the current to flow from the HTR fuse to TERMINAL 1 of the HTR relay to TERMINAL 2 to TERMINAL 1 of the blower motor
to TERMINAL 2 to TERMINAL 5 of the blower SW to TERMINAL 1 to GROUND, rotating the blower motor at high speed.
2. FAN MOTOR OPERATION
When the ignition SW is turned on, the current from the ECU-IG fuse flows to the FAN NO.1 relay (Coil side) and the A.C FAN NO.2 relay (Coil
side) to TERMINAL 3 of the A/C single pressure SW to TERMINAL 2 to engine control module. Electric current passed to engine control
module receives the signal from engine coolant temperature sensor and is sent from engine control module to GROUND, and the FAN NO.1 relay
is turned off and the A.C FAN NO.2 relay is turned on.
At the same time as this current flow, the current from the ECU-IG fuse flows to the ENGINE MAIN relay (Coil side) to GROUND, turning the
ENGINE MAIN relay on. As a result, current from the FL ALT fuse flows to the CDS fuse and RDI fuse.
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Low speed operation
When the ignition SW is turned on and the A/C is activated, the current flows from the FL ALT fuse to the HTR fuse to the HTR relay (Point
side) to the A.C fuse to the A.C MG relay (Point side) to the A.C FAN NO.3 relay (Coil side) to GROUND, turning the A.C FAN NO.3 relay
on. As a result, the current from the CDS fuse flows to TERMINAL 2 of the A/C condenser fan motor to TERMINAL 1 to the A.C FAN NO.2
relay (Point side) to the A.C FAN NO.3 relay (Point side) to TERMINAL 2 of the radiator fan motor to TERMINAL 1 to GROUND. As a
result, the fans are activated at low speed. If the engine coolant temperature is approx. 90 °C (194 °F) or less, and the refrigerant pressure is
approx. 15.5 kg/sq.cm (220 psi, 1520 kPa) or less, both the water temperature SW (Radiator fan) and the A/C single pressure SW are closed,
so the FAN NO.1 relay is turned off and the A.C FAN NO.2 relay is turned on. As a result, each fan motor operates at low speed.
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High speed operation
During A/C operation, if the refrigerant pressure becomes higher than ordinary level (Approx. 15.5 kgflcm2 (220 psi, 1520 kPa)), the A/C
single pressure SW is turned off. As a result, the FAN NO.1 relay is turned on and the A.C FAN NO.2 relay is turned off, and the current flows
from the RDI fuse to FAN NO.1 relay (Point side) to TERMINAL 2 of the radiator fan motor to TERMINAL 1 to GROUND, and the current
from the CDS fuse flows to TERMINAL 2 of the A/C condenser fan motor to TERMINAL 1 to A.C FAN NO.2 relay (Point side) to
GROUND, reaching each fan motor in parallel, thus causing the fan motors to operate at high speed.
Note that, because the current flows in the same manner even if the engine coolant temperature is approx. 90 °C (194 °F) or higher, the fan
motors still operate at high speed.
3. AIR INLET CONTROL SERVO MOTOR OPERATION
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Switching from FRESH to RECIRC