Blower Motor Circuit
SYSTEM DESCRIPTION
Component 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
For description of system operation, see next page.
RHA168F
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 12V), the automatic amplifier supplies a signal to the fan con-
trol 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.
GI
MA
EM
LC
EC
FE
AT
PD
FA
RA
BR
ST
RS
BT
EL
IDX
TROUBLE DIAGNOSES
HA-113