Blower Motor Voltage Protection Mode Conditions
Voltage at the Motor
Results
under 8.5 VDC
Blower motor will shut off and will not restart until the voltage reaches 10.5 VDC and will operate at
reduced speed if voltage is under 12 VDC.
8.5 to 12.0 VDC
Blower motor will operate at reduced speed. The reduced speed varies with voltage. The lower the
voltage, the slower the blower speed.
12.0 to 17.0 VDC
Blower motor operates normally at user selected speed.
over 17.0 VDC
Blower motor will shut off. Will not restart until voltage reaches 16 VDC.
Table 1, Blower Motor Voltage Protection Mode Conditions
Blower Motor Feedback Signal From Blower to FCU or ACU
*
Speed/Error
Conditions
Signal
Duty Cycle
Blower Speed
Three one-millisecond pulses per revolution. Blower speed is determined by the
time between each set of three pulses. Time can be viewed using an oscilloscope.
rpm=1/(time between sets of three pulses) x 60
NA
Error—temperature
protection mode
10Hz
25%
Error—voltage
protection mode
10Hz
50%
Error—blocked rotor
10Hz
75%
*
Blower speed and diagnostic information are both provided by the BLDC blower motor on the feedback signal wire; however, the FCU and ACU only use the
blower speed information.
Table 2, Blower Motor Feedback Signal from Blower to FCU or ACU
Blower Speed Control Signal From FCU or ACU to Blower
*†
Knob Position
FCU Signal (DC
volts)
‡
Blower Speed (rpm)
Blower Speed Comments
0
0.0 to 0.74
0
Constant speed in this range
1
0.75 to 1.0
400
Constant speed in this range
2
1.5
800
Speed varies linearly with voltage in this range.
3
2.0
1200
4
2.5
1600
5
3.0
2000
6
3.5
2400
7
4.0
2800
8
4.5
3200
9
5.0+
3600
Heater and Air Conditioner Troubleshooting
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Electrical System Tests
122SD and Coronado Workshop Manual, Supplement 9, June 2014
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