Low Pressure Switch (S87) Sequence Of Operation (All Versions) - Lennox XP25-024-230-01 Installation And Service Procedure

PRESSURE
Y1 DEMAND
SWITCH (S87)
CONTACTOR
DE-ENERGIZED
OPEN
ANTI-SHORT
CYCLE TIMER
BEGINS
INCREMENT
5-STRIKE
COUNTER
LED ALERT
CODE / OR
MODERATE
ALERT 410
DISPLAYED
ANTI-SHORT
CYCLE TIMER
ENDS
CONTACTOR
ENERGIZED
PRESSURE
SWITCH (S87)
SERVICE
2
REQUIRED
WAITING FOR
PRESSURE
OPEN
SWITCH TO
CLOSE
Figure 35. Low Pressure Switch (S87) Sequence of Operation (All Versions)
LOW
CLOSED
LOW
PRESSURE
OPEN
SWITCH (S87)
The thermostat terminates demand when the contactor is
1.
de-energized. If demand is satisfied when alarm is not active, the
5-strike counter resets.
2. Lockouts can be reset by cycling power off to the outdoor control
(A175) R terminal.
3. The low pressure switch is ignored by the system when the out­
door temperature is below 15°F.
REACHES 5
WITHIN A SINGLE
1
Y1 DEMAND
SWITCH (S87)
LOW
CLOSED
CLOSED
CONTACTOR
ENERGIZED
CLOSED
5-STRIKE
COUNTER
LOW
PRESSURE
LOCKOUT
LED ALERT
CODE / OR
CRITICAL
REQUIRED
ALERT 411
DISPLAYED
LED ALERT
CODE / OR
MODERATE
ALERT 410
DISPLAYED
Page 57
INITIAL TRIP
SWITCH IS
IGNORED FOR
90 SECONDS
SWITCH IS CLOSED OR OUTDOOR
AMBIENT TEMPERATURE IS 15ºF
OR BELOW
SERVICE
2
NORMAL
OPERATION
3
XP25