Lennox XC21 Installation Instructions Manual page 43

2. Verify LED RPM indicator is displaying the correct
flash sequence for the applicable size unit (see table
table 16).
3. Test DC voltage output on the A177 fan motor control's
J2 terminals (see figure 24) while under full load and
verify the voltage read to the voltage listed in table 16
for the applicable size unit.
4. If no voltage is detected at the J2 terminals, verify
there is a Y1 demand at the thermostat and applicable
voltages detected all A177 fan motor control voltage
inputs, see table 12. NOTE: Voltage will be present at
specific inputs depending on the type of demand (low
or high stage and EDA operation).
5. If there is a demand, proceed to the next section for
further testing.
VERIFYING CORRECT INPUT VOLTAGE (ECM/Y1,
ECM/Y2, ECM C AND EXT ECM/R)
Using a volt meter, check voltages on the following A177
fan motor control inputs using table 12. Voltage will only be
present during a thermostat demand. See figure 25 for test
example.
Flash or Pause State
Flash Flash
Slow Flash
Short Pause
Long Pause
Unit Status
Mismatched RPM
CRC Failure
Table 15. A177 Fan Motor Control Stage Operation LED Indicator Codes
Unit Status
Two Stage Operation
Table 16. Two Stage
CFM Profile Pin Select
Application
4
XC21−024 ON
XC−036 ON
XC21−048 and
ON
XC21−060
* LED Code indicates A177 Fan Motor Control LED flash sequence. For example, LED Code 9 indicates 9 slow flashes and pause.
Table 13. A177 Fan Motor Control Flash and Pause Durations
Table 14. A177 Fan Motor Control Error/Fault LED Codes
A177 Fan Motor Control LED
Fast Flash with no pause
Unit Status
Low Stage
High Stage
EDA Operation
A177 Fan Motor Control RPM Jumper Settings, LED RPM Indicator and
P2 DC Voltage Outputs
Low Stage
3 2 1 RPM
ON OFF OFF 475
OFF ON ON 525
OFF OFF ON 600
If correct voltage is present at A177 fan motor control
inputs and no voltage or incorrect voltages are present at
J2 output, replace A177 fan motor control.
Table 12. A177 Fan Motor Control Voltage Inputs
Input
ECM/Y1 and ECM C
(Low Stage)
ECM/Y1 − ECM/Y2 and
ECM C
(High Stage)
ECM/Y2 and ECM C
(EDA Operation)
EXT ECM/R and ECM C
Constant ON.
ECM1/Y1 ONLY
ECM1/Y1 and ECM2/Y2
ECM2/Y2 ONLY
ECM1/Y1 High Stage
Only
LED
DC Volt RPM
Code
6 15.1 550
7 16.8 600
8 19.2 675
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Thermostat
Demand
YES
NO
YES
NO
YES
NO
YES
NO
Duration
Three flashes per second
One flash per second
Two seconds of OFF time.
Five seconds of OFF time.
Possible Cause
Internal feedback, PWM does not match tar-
get.
Microcontroller CRC failure.
A177 Fan Motor Control LED
One slow flash, then short pause.
Two slow flash, then short pause.
Three slow flash, then short pause.
EDA Operation
ECM1/Y1
ECM2/Y2 Only
and ECM2/Y2
LED
DC Volt RPM
Code
8 17.6 200
8 19.2 225
9 21.6 225
Voltage
Present
24VDC
NONE
24VDC at each
input
NONE at each
input
24VDC
NONE
24VAC
NONE
LED
DC Volt
Code
3 6.3
3 7.0
3 7.0
XC21 SERIES