Fan Speed Control

Fan Speed Control System - Auto A/C:

FAN SPEED CONTROL
Blower speed is automatically controlled based on temperature setting, ambient temperature, in-vehicle temperature, intake air temperature, amount of sunload and air mix door position.

With FAN switch set to "AUTO", the blower motor starts to gradually increase air flow volume. When engine coolant temperature is low, the blower motor operation is delayed to prevent cool air from flowing.

Component Parts:
1) Auto amp.
2) Fan control amplifier
3) Potentio Balance Resistor (PBR)
4) In-vehicle sensor
5) Ambient sensor
6) Intake sensor
7) Sunload sensor
8) Blower Hi-relay
9) Thermal transmitter

SYSTEM OPERATION
Automatic Mode
In the automatic mode, the blower motor speed is calculated by the auto amp. based on inputs from the PBR, in-vehicle sensor, intake sensor, sunload sensor, and ambient sensor. The blower motor applied voltage ranges from approximately 4.5 volts (lowest speed) to 12 volts (highest speed).

To control blower speed (in the range of 4.5 volts to 10.5 volts), the auto amp. supplies a signal to the fan control amplifier. Based on this signal, the fan control amplifier controls the current flow from the blower motor to ground.

If the computed blower voltage (from the automatic amplifier) is above 10.5 volts, the high blower relay is activated. The high blower relay provides a direct path to ground (bypassing the blower amplifier), and the blower motor operates at high speed.

Starting Fan Speed Control
"Cold Soak" Condition (Automatic Mode)
In a cold start up condition where the engine coolant temperature is below 50°C (122°F), the blower will not operate for a short period of time (up to 180 seconds). The exact start delay time varies depending on the ambient and engine coolant temperature.

In the most extreme case (very low ambient) the blower starting delay will be 180 seconds. After this delay, the blower will operate at low speed until the engine coolant temperature rises above 50°C (122°F). Then the blower speed will increase to the objective speed.

"Hot Soak" Condition (Automatic mode)
The blower will begin operation momentarily after the AUTO button is pushed. The blower speed will gradually rise to the objective speed over a time period of 5 seconds or less (actual time depends on the objective blower speed).

Blower Speed Compensation
Sunload
When the in-vehicle temperature and the set temperature are very close, the blower will operate at low speed. The low speed varies depending on the sunload. During conditions of high sunload, the blower low speed is "normal" low speed (approx. 5.5 volts). During lesser sunload conditions, the low speed will drop to "low" low speed (approx. 4.5 volts).