Page 77
XP21
Y1 DEMAND
LOW
PRESSURE
SWITCH (S87)
COMPRESSOR
CONTACTOR
ENERGIZED
INITIAL TRIP
SWITCH IS
IGNORED FOR
90 SECONDS
LOW
PRESSURE
SWITCH (S87)
COMPRESSOR
CONTACTOR
DE−ENERGIZED
COMPRESSOR
ANTI−SHORT
CYCLE TIMER
BEGINS
INCREMENT
5−STRIKE
COUNTER
1
LED ALERT
CODE / OR
MODERATE
ALERT 410
DISPLAYED
ANTI−SHORT
CYCLE TIMER
ENDS
COMPRESSOR
CONTACTOR
ENERGIZED
LOW
PRESSURE
SWITCH (S87)
WAITING FOR
PRESSURE
SWITCH TO
CLOSE
SWITCH IS CLOSED OR OUTDOOR
AMBIENT TEMPERATURE IS 15ºF
OR BELOW
5−STRIKE
COUNTER
REACHES 5
WITHIN A SINGLE
Y1 DEMAND
LOW
PRESSURE
SWITCH (S87)
LOCKOUT
LED ALERT
CODE / OR
CRITICAL
ALERT 411
DISPLAYED
SERVICE
REQUIRED
2
LED ALERT
CODE / OR
MODERATE
ALERT 410
DISPLAYED
SERVICE
REQUIRED
2
NORMAL
OPERATION
CLOSED
CLOSED
OPEN
OPEN
1
If 5−strike counter has four or less strikes when Y1 demand
is terminated or satisfied, the strike counter will reset to
zero. In a icomfort setup, the thermostat will terminate
demand when the compressor contactor is de−energized. If
demand is satisfied when alarm is not active, the 5−strike
counter will reset.
2
Lockouts can be reset by either cycling power off to the
heat pump control’s (A175) R terminal, or placing a jumper
on the field test pins (E33) between 1 to 2 seconds.
OPEN
CLOSED
CLOSED
Figure 43. Low Pressure Switch (S87) Sequence of Operation (All Versions)
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