Blower Motor: Description and Operation
SYSTEM DESCRIPTIONComponent parts
Fan speed control system components are:
1. Auto amplifier
2. Fan control amplifier
3. A/C LAN system (PBR)
4. In-vehicle sensor
5. Ambient sensor
6. Sunload sensor
7. Intake sensor
8. Thermal transmitter
9. A/C control unit (PTC, AUTO, ECON, MODE, DEFROST, BLOWER, OFF switches)
System Operation:
Automatic mode
In the automatic mode, the blower motor speed is calculated by the automatic amplifier based on inputs from the PBR, in-vehicle sensor, sunload sensor, and ambient sensor. The blower motor applied voltage ranges from approximately 4 volts (lowest speed) to 12 volts (highest speed).
The control blower speed (in the range of 4 to 12 V), the automatic amplifier 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 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 fan control amplifier), and the blower motor operates at high speed.
Starting blower speed control
Start up from "COLD SOAK" condition (Automatic mode)
In a cold start up condition where the engine coolant temperature is below 56 °C (133 °F) and the ambient temperature is below 15 °C (59 °F), the blower will not operate for a short period of time (up to 90 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 as described above.
After this delay, the blower will operate at low speed until the engine coolant temperature rises above 32 °C (90 °F), at which time 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 3 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 be operating at low speed. The low speed will vary depending on the sunload. During conditions of high sunload, the blower low speed is "normal" low speed (approx. 6 V). During low or no sunload conditions, the low speed will drop to "low" low speed (approx. 5 V).
Ambient
When the ambient temperature is in the "moderate" range [10 - 15 °C (50 - 59 °F)], the computed blower voltage will be compensated (reduced) by up to 3.5 V (depending on the blower speed). In the "extreme" ambient ranges [below 0 °C (32 °F) and above 20 °C (68 °F)] the computed objective blower voltage is not compensated at all. In the ambient temperature ranges between "moderate" and "extreme" [0 - 10 °C (32 - 50 °F) and 15 - 20 °C (59 - 68 °F)], the amount of compensation (for a given blower speed) varies depending on the ambient temperature.
Fan Speed Control Specification:
COMPONENT DESCRIPTION
Fan control amplifier
The fan control amplifier is located on the cooling unit. It amplifies the base current flowing from the auto amplifier to change the blower speed within the range of 4 V to 12 V.