Troubleshooting - Lennox SL280UHNV Series Unit Information

Troubleshooting: Heating Sequence of Operation (Continued)
ONLY FOR 1ST
REQUEST FOR
2ND STAGE HEAT
CALL FOR SECOND-STAGE HEAT
2
CALL FOR 2ND STAGE HEAT
(HIGH FIRE)
SINGLE STAGE
2 STAGE THERMOSTAT
THERMOSTAT
RECOGNITION DELAY
(30 SECONDS)
EXPIRED?
YES
YES
INDUCER SWITCHED
TO HIGH SPEED
HIGH
PRESSURE SWITCH
CLOSED WITHIN 10
SECONDS?
YES
2ND STAGE GAS VALVE
ENERGIZED
INDOOR BLOWER ENERGIZED
ON HIGH HEAT SPEED
3
CALL FOR HEAT SATISFIED
1
SYSTEM WILL ALWAYS LIGHT ON LOW FIIRE, EVEN IF 2ND STAGE HEAT IS IN PLACE.
2 WHEN USED WITH A SINGLE STAGE THERMOSTAT, SET SW1 TO THE ON POSITION IN DIP SWITCH S4.
3 IF THE HIGH FIRE PRESSURE SWITCH DOES NOT CLOSE WITHIN 5 ATTEMPTS, THE SYSTEM WILL OPERATE AT
LOW FIRE FOR THE REMAINDER OF THE CALL FOR HEAT REQUEST.
1
2
2ND STAGE
ON DELAY
EXPIRED?
INDUCER SWITCHED
NO
TO LOW SPEED
Page 50
5 MINUTE DELAY
3
(ERROR CODE FLASHES)