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Y1 DEMAND
OR COOLING
DEMAND
OPEN
SERVICE
2
REQUIRED
OPEN
Figure 31. Low Pressure Switch (S87) Sequence of Operation (All Units)
31-5000750 Rev. 1
LOW
PRESSURE
CLOSED
CLOSED
(S87)
LOW PRESSURE
OPEN
CONTACTOR
DE-ENERGIZED
1.
2.
ANTI-SHORT
CYCLE TIMER
3.
BEGINS
INCREMENT
5-STRIKE
1
COUNTER
LED ALERT
CODE / OR
SERVICE SOON
ALERT 410
DISPLAYED
ANTI-SHORT
CYCLE TIMER
ENDS
CONTACTOR
ENERGIZED
LOW PRESSURE
CLOSED
SWITCH
S87
WAITING FOR
PRESSURE
TO RISE ABOVE
40 PSIG
NO
CONTACTOR
ENERGIZED
CLOSED
(S87)
The thermostat terminates demand when the contactor
is de-energized. If demand is satisfied when alarm is
not active, the 5-strike counter resets.
door control (A175) R terminal.
The low pressure switch is ignored when
the outdoor temperature is below 15°F.
5-STRIKE
COUNTER
REACHES 5
WITHIN A SINGLE
Y1 DEMAND
LOW
PRESSURE
LOCKOUT
LED ALERT
CODE / OR
SERVICE URGENT
ALERT 411
DISPLAYED
LED ALERT
CODE / OR
SERVICE SOON
ALERT 410
DISPLAYED
CLOSED
SUCTION
PRESSURE
CUT-OUT IS
IGNORED FOR
90 SECONDS
SWITCH IS CLOSED OR
OUTDOOR AMBIENT
TEMPERATURE IS 15ºF
OR BELOW
SERVICE
2
REQUIRED
NORMAL
OPERATION
3
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