Inducer Motor Drive Board Led Functions - Trane ACONT900AC43UA Service Manual

Solving Err 91 Comm Errors
Troubleshooting Chart IND COMM ERR

Inducer motor drive board LED functions

If the green COM LED on the inducer motor drive
board is flashing, this is an indication that the inducer
motor drive board and the gas furnace IFC are com-
municating with each other. The inducer motor drive
COM LED will continue to flash as long as there is a
call for heat.
The inducer motor drive board RED STOP LED will
flash on and off a few times when the gas furnace
IFC sends a command to turn off the inducer motor.
The RED STOP LED is normally off.
Step 1
Turn power ON.
Is there 12 VD at the inducer motor drive board
terminals VCC and GND? (See Figure 4.)
Figure 4
Yes: Go to Step 2.
R - B 4
No: Go to Step 7.
Step 2
Turn power ON.
Is there 120 VAC at the inducer motor drive board
terminal L1 and L2? (See Figure 5.)
Figure 5
Yes: Go to Step 3.
No: Repair as needed and retest.
Step 3
Cycle power to the Comfort Control thermostat and
set it to call for heat.
Is there DC voltage between the inducer motor
drive board terminals RX and GND? (See Figure
6.) This DC voltage should be going up and down
between 0.2 volts DC and 1.7 volts DC*.
*Note: Voltage levels may vary depending upon volt
OHM meter type.