Blower Motor: Description and Operation
Component partsFan speed control system components are:
1. Auto amp.
2. Fan control amplifier
3. A/C LAN system (PBR built-in mode door motor and air mix door motor)
4. In-vehicle sensor
5. Ambient sensor
6. Sunload sensor
7. Intake sensor
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, 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, the auto amp. supplies a signal (in the range of 2.5V to 9V), to the fan control amplifier. Based on this signal, the fan control amplifier controls the current flow from the blower motor to ground.
STARTING FAN SPEED CONTROL
Start up from "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 150 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 150 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.
Start up from normal or "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. 5.5V). During lesser sunload conditions, the low speed will drop to "low" low speed (approx. 4.5V).
Fan speed control specification
FAN CONTROL AMPLIFIER
The fan control amplifier is located on the cooling unit. It amplifies the base current flowing from the auto amp. to change the blower speed within the range of 4V to 12V.