035-19671-002 Rev. A (0704)
Unitary Products Group
9
FIGURE 8:
Furnace Control Event Schedule
W2 SIGNAL
ON
CLOSED
OPEN
OPEN
CLOSED
ABSENT
PRESENT
HIGH INDUCER
HIGH STAGE PRESSURE
SWITCH AND 2ND STAGE
MAIN VALVE
CIRCULATOR HIGH
HEAT SPEED
2ND STAGE
CALL HIGH HEAT AFTER LOW
HEAT IS ESTABLISHED
HIGH
HEAT
OFF
DELAY
30 SEC.
HIGH LIMIT
W1 SIGNAL
LOW
INDUCER
LOW STAGE
PRESSURE
SWITCH
HSI
1ST STAGE
MAIN VALVE
FLAME
SENSE
LOW CIRCULATOR
HEAT SPEED
1ST STAGE
LOW PRESSURE
SWITCH CLOSE
RECOGNITION
HSI
WARM
UP
17 SEC.
IGNITION
ACTIVATION
PERIOD
4 SEC.
TRIAL FOR
IGNITION
7 SEC.
INTER-
PURGE
60 SEC.
HSI
WARM
UP
27 SEC.
IGNITION
DEACTIVATION
PERIOD
3 SEC.
HEAT FAN
DELAY ON
30 SEC.
BURN
TIME
POST
PURGE
15 SEC.
HEAT FAN DELAY OFF
SELECTABLE
60,90,120,180 SEC.
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
NOTE:
1. THIS DIAGRAM SHOWS TWO IGNITION ATTEMPTS
2. TIMING LENGTHS ARE NOT TO SCALE
