York AHV8 UH Series User's Information, Maintenance And Service Manual page 9

W2 SIGNAL
HIGH INDUCER
HIGH STAGE PRESSURE
SWITCH AND 2ND STAGE
MAIN VALVE
CIRCULATOR HIGH
HEAT SPEED
2ND STAGE
HIGH LIMIT
W1 SIGNAL
LOW
INDUCER
LOW STAGE
PRESSURE
SWITCH
HSI
1ST STAGE
MAIN VALVE
FLAME
SENSE
LOW CIRCULATOR
HEAT SPEED
1ST STAGE
NOTE:
1. THIS DIAGRAM SHOWS TWO IGNITION ATTEMPTS
2. TIMING LENGTHS ARE NOT TO SCALE
FIGURE 8: Furnace Control Event Schedule
Unitary Products Group
ON
OFF
ON
OFF
ON
OFF
ON
OFF
CALL HIGH HEAT AFTER LOW
HEAT IS ESTABLISHED
CLOSED
OPEN
ON
OFF
ON
OFF
CLOSED
OPEN
ON
OFF
ON
OFF
PRESENT
ABSENT
ON
OFF
HSI
WARM
UP
17 SEC.
LOW PRESSURE
SWITCH CLOSE
RECOGNITION
IGNITION
ACTIVATION
TRIAL FOR
PERIOD
IGNITION
4 SEC.
7 SEC.
INTER- HSI HEAT FAN
PURGE WARM DELAY ON
60 SEC. UP 30 SEC.
27 SEC.
IGNITION
DEACTIVATION
PERIOD
3 SEC.
271002-UUM-A-0407
HIGH
HEAT
OFF
DELAY
30 SEC.
BURN
TIME
POST
PURGE
15 SEC.
HEAT FAN DELAY OFF
SELECTABLE
60,90,120,180 SEC.
9