Troubleshooting; Unit Fails To Operate In The Cooling, Heating, Or Continuous Fan Mode - Lennox G60UHV Service Manual

IX− Troubleshooting
Two Stage Variable Speed Control Boards 18M99 & 49M59
UPON INITIAL POWER UP, REMOVE ALL THERMOSTAT DEMANDS TO THE UNIT
PROBLEM: 1 UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE
Condition
1.1
− Both diagnostic lights fail to light up.
LED#1−Off
LED#2−Off
1.2
− Diagnostic lights flash the reverse
polarity code.
LED#1−Fast Flash,
LED#2−Slow Flash.
1.3
− Diagnostic lights flash the improper
main ground.
LED#1−Alternating Fast Flash
LED#2−Alternating Fast Flash
Possible Cause
1.1.1
Main voltage 120V not supplied to unit.
1.1.2
Miswiring of furnace or improper con-
nections.
1.1.3
Circuit breaker tripped or fails to
close.
1.1.4
Door interlock switch failure.
1.1.5
Transformer Failure.
1.1.6
Failed control board.
1.2.1
120V main power polarity reversed.
1.3.1
Improper ground to the unit.
1.3.2
Open ignitor circuit.
1.3.3
Broken or failed ignitor.
1.3.4
Line voltage is below 75V.
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Corrective Action / Comments
ACTION 1 − Check 120V main voltage.
Determine cause of main power failure.
ACTION 1 − Check for correct wiring of 120V to
power make up box and transformer.
ACTION 2 − Check 24V wiring to control board.
ACTION 1 − Replace circuit breaker if it is reset
but does not have continuity.
ACTION 2 − If circuit breaker still trips, check for
short.
ACTION 1 − Check that door switch is activated
when door is closed.
ACTION 2 − Check wire connections to switch, re-
place loose connectors.
ACTION 3 − Check continuity of switch in closed
position. Replace if defective.
ACTION 1 − Check that transformer output is
24V. Replace if defective.
ACTION 1 − If all the above items have been
checked, replace board.
ACTION 1 − Check the 120V has line and neutral
correctly input into control.
ACTION 2 − Reverse the line and neutral at the
120V field connection.
ACTION 1 − Check that the unit is properly ground.
ACTION 2 − Install a proper main ground to the unit
ACTION 1 − Check for correct wiring and loose
connections in the ignitor circuit. Check mult−plug
connections for correct installation.
ACTION 1 − Unplug ignitor and read resistance
across ignitor. If resistance does not read between
10.9 and 19.7 ohms, replace the ignitor.
ACTION 1 − Check that the line voltage is above
75V. Determine cause of voltage drop and supply
correct voltage to the control.