506860-03
Issue 1946
Page 19 of 27
Code
Diagnostic Codes / Status of Equipment
Action Required to Clear and Recover
E416
The outdoor coil sensor is either open, short-circuited
or the temperature is out of sensor range. As a result,
the outdoor unit control will not perform any defrost
tempering.
Coil sensor being detected open or shorted, or temperature is
out of coil sensor range. Outdoor unit control will not perform
demand or time/temperature defrost operation. System will
still heat or cool. Check the resistance of the coil sensor and
compare to temperature resistance chart. Replace coil sensor
if needed. The alarm clears when outdoor unit control detects
proper coil sensor readings or after a power reset.
E417
The outdoor unit discharge sensor is either open, short-
circuited or the temperature is out of sensor range. As a
result, the outdoor unit control will not perform any defrost
tempering.
Outdoor unit control detects open or shorted discharge
sensor, or temperature that is out of discharge sensor range.
Check the resistance of the discharge sensor and compare
to temperature resistance chart; replace if needed. Reset
by replacing the discharge sensor. This fault is detected
by allowing the unit to run for 90 seconds before checking
discharge sensor resistance. If the discharge sensor
resistance is not within range after 90 seconds, the board will
count one fault. After 5 faults, the board will lock out. Check
for proper sensor reading and attachment to line. The alarm
clears after a power reset.
E418
There is a faulty W output circuit.
Faulty W output circuit. Confirm that the unit is not running.
Check for mis-wiring. Disconnect thermostat lines from W
and verify 24VAC on the W. If 24VAC is present, replace the
board.
E419
The W output on the outdoor unit has reported more
than 5 errors. As a result, the system has shut down the
outdoor unit.
W output hardware fault count reached 5 strikes.
E420
The heat pump defrost cycle has taken more than 20
minutes to complete.
Defrost cycle lasts longer than 20 minutes. This alarm is
applicable with non-communicating heat pump system only.
Check heat pump defrost operation. The alarm is cleared after
the “W1” signal is removed.
E421
The W output terminal on the outdoor unit is not wired
correctly.
Voltage sensed on W and O when Y1 thermostat input is
deactivated. Another device or wiring fault is energizing W
check wiring. The alarm clears when wiring is corrected or
after a power reset.
NOTE
:
Additional codes may be found in the Comfort Sync room thermostat manual.
Table 5. 7-Segment Alert and System Status Codes
