Climate Control Systems, System Specific

Blower Controls

With the Ignition Switch in RUN, battery voltage is applied through Fuse 20 to the Blower Speed Control at connector C2 and terminal 3 on connector C1, to the Heater Final Stage at terminal 5, and to the A/C Final Stage at terminal 4. When the Blower Speed Control is set to SLOW, a very low voltage (less than 1 volt) is output at terminal 1 on connector C1 to the A/C Selector Switch. If the A/C Selector Switch is in the HEAT position (not depressed), the low voltage from the Blower Speed Control is directed to the Heater Final Stage at terminal 2.

The Heater Final Stage determines the amount of voltage applied to the Heater Blower Motor and also provides the current to operate the Motor. The voltage applied is approximately 0.7 volts less than the input voltage to the Heater Final Stage at terminal 2. The Heater Blower Motor is grounded through the normally closed contacts of the Blower Select Relay.

Both the Heater Blower Motor and the A/C Blower Motor are variable speed Motors that run at a speed proportional to the applied voltage. At low applied voltage, the Blower Motor runs at very low speed.

As the Blower Speed Control is increased toward FAST, the output voltage at terminal 1 on connector C1 of the Blower Speed Control gradually increases to a maximum of about 10 volts, which is applied to the input of the Heater Final Stage. The output voltage from the Heater Final Stage increases at a level approximately 0.7 volts less than the input and drives the Heater Blower at faster speed.

If the Blower Speed Control is moved to the maximum speed position (fully clockwise), battery voltage at connector C2 is applied through the Blower Speed Control and then directly to the Heater Blower. The Heater Blower runs at maximum speed.

When the A/C Selector Switch is in COOL (depressed), battery voltage at Fuse 19 is applied through the A/C Selector Switch at terminals 4 and 6 to the coil of the Blower Select Relay and to the Minimum Blower Speed Input Enable at terminal 2 on connector C1 of the Blower Speed Control.

Operation of the Blower Select Relay removes the ground from the Heater Blower Motor (BR/RD wire) and grounds the A/C Blower Motor (BR/BK wire). At the same time, a different section of the A/C Selector Switch directs the Blower Speed Output at terminal 1 on connector C1 of the Blower Speed Control to the input (terminal 6) of the A/C Final Stage.

Operation of the A/C Final Stage is similar to that of the Heater Final Stage. The Blower Speed Control now controls the speed of the A/C Blower instead of the Heater Blower. The only exception to the operation is that at minimum speed the output from the Blower Speed Control does not drop below approximately 3 volts. This ensures that blower speed does not drop so low that freezing of the Evaporator takes place.

Temperature Control

The in-car temperature is controlled by the Heater Regulator and Evaporator Temperature Regulator. In Heater mode operation

(A/C Selector Switch not depressed), the temperature of air flow into the car is determined by the operation of the Water Shutoff Valve. If the in-car temperature is significantly lower than the setting of the Temperature Selector Control, the Water Shutoff Valve remains open (de-energized), allowing a continuous flow of engine coolant through the heater core. As the in-car temperature approaches the setting of the Temp Select Control, the Heater Regulator grounds terminal 1 at about 4-second intervals, which energizes the Water Shutoff Valve at the same rate. The intermittent flow of engine coolant through the heater core reduces the average temperature of the air flow into the car. If the in-car temperature rises above the setting of the Temp Select Control, the Heater Regulator will ground terminal 1 continuously, shutting off the coolant flow through the heater core. In-car and heater core temperatures are input to the Heater Regulator at terminals 6 and 7.

In A/C mode operation (A/C Selector Switch depressed), battery voltage is applied to terminal 4 of the Heater Regulator, indicating that the Water Shutoff Valve should be energized continuously. This removes all heat from the heater core. Battery voltage is also applied to terminal 4 of the Evaporator Temperature Regulator. When the setting of the Temp Select Control is below the in-car temperature, the voltage at terminal 3 of the Evaporator Temperature Regulator is at a level which enables the Compressor Control output. Battery voltage is then applied from terminal 5 to the Compressor Clutch through the High Pressure Cutout Switch and the Temperature Switch (S38 engine).

The High Pressure Cutout Switch opens if refrigerant pressure rises to a value which is too high for normal operation. The Temperature Switch (S38 Engine) opens to remove the Compressor load from the engine if the engine coolant temperature rises above 226 °F (108 °C). The Evaporator Temperature Sensor signals the Evaporator Temperature Regulator to deenergize the Compressor Clutch when evaporator temperature is low enough that freezing may result.