Heating and Air Conditioning: Description and Operation

1. HEATER BLOWER MOTOR OPERATION
With the Ignition SW ON, current from the GAUGE fuse flows to TERMINAL 3 of the Heater Relay to TERMINAL 1 to TERMINAL 1 of the Heater Blower SW.

(Low Speed Operation)
When the Heater Blower SW is moved to the low speed position, the current applied to TERMINAL 1 of the heate blower SW flows from TERMINAL 8 to GROUND, causing the Heater Relay to come ON. Then the current flowing from the HEATER fuse flows to TERMINAL 5 of Heater Relay to TERMINAL 4 to TERMINAL 1 of the Blower Motor to TERMINAL 2 to TERMINAL 1 of the Blower resistor to TERMINAL 4 to GROUND, causing the Blower motor to rotate.
At this time, the current flows against the full resistance of the Blower Resistor, so the motor turns slowly at low speed.

(Operation At Speed M1, M2)
When the Heater Blower SW is moved to the speed M1 position, the current applied to TERMINAL 1 of the heater blower SW flows to TERMINAL 8 to GROUND, turning the Heater Relay to ON. Then, the same as with low speed, current passes from the Blower Motor to TERMINAL 1 of the Blower Resistor to TERMINAL 2 to TERMINAL 3 of the Heater Blower SW to TERMINAL 8 to GROUND. At this time, the resistance of the Blower resistor is less than it is for low speed, so the Blower Motor rotates faster than it does at low speed. With the Heater Blower SW in the M2 position, current flowing through the motor flows from TERMINAL 1 of the Blower Resistor to TERMINAL 3 to TERMINAL 2 of the Heater Blower SW to TERMINAL 8 to GROUND. At this time, resistance of the Blower Resistor is less than for speed M1 so the Blower Motor rotates faster than for speed M1.

(High Speed Operation)
With the Heater Blower Switch in high speed position, until the Heater Relay comes ON and current flows to the Blower Motor, operation is the same as for speed M1 and M2. The current passing through the Blower Motor flows to TERMINAL 6 of the Heater Blower SW to TERMINAL 8 to GROUND without flowing through the Blower Resistor, so that the Blower Motor rotates at the fastest speed, high speed.

2. AIR CONDITIONING OPERATION
When the Blower SW is set to ON, current from the HEATER fuse flows through the A/C fuse to TERMINAL 1 of the A/C Dual Pressure SW to TERMINAL 2 to TERMINAL 1 of the A/C Amplifier. The engine speed signal from the igniter and the evaporator temp. signal from the A/C thermistor are all supplied to the A/C amplifier. When the A/C SW is turned ON, the A/C SW ON signal is sent to activate the A/C amplifier. Current flows from the A/C amplifier to the magnetic clutch, turning the compressor ON. The A/C operation is shut OFF when a signal indicating low evaporator temp., or abnormally High or Low refrigerant pressure, is supplied while the engine high speed signal exists. When one of these signals is received, the amplifier shuts OFF the A/C operation.