4-14
Sequence of Operation
µ
P-D Controller
CRR-20 & CRR-40, September 1999
Modulation Cool
• Controller calls for Modulation Cool when the Calculated
Temperature Differential is between 10.0 C (17.9 F)
above setpoint and setpoint (after initial temperature pull-
down).
• Controller opens and closes the KVQ valve to regulate
the flow of refrigerant to the compressor. The position
of the KVQ valve balances the unit cooling capacity
against the actual load requirements.
• Controller turns ON the In-range LED when the control-
ling sensor temperature is within 1.7 C (3.0 F) of set-
point. The controller keeps the In-range LED ON as
long as the supply air temperature remains less than 2.5
C (4.5 F) above setpoint. If the supply air goes out-of-
range high, the In-range LED remains OFF until the sup-
ply air temperature decreases to 1.7 C (3.0 F) above set-
point.
NOTE: If the supply air sensor temperature goes
out-of-range high for 75 minutes after the unit is
In-range, the controller will turn ON the Alarm
LED. Alarm code 12 (a check alarm) is also
recorded in the controller’s memory.
Null
• The controller calls for Null when the Calculated
Temperature Differential is between setpoint and 0.6 C
(1.0 F) below setpoint (on temperature pull-down).
• The controller de-energizes the liquid line solenoid valve
to pump down the low side.
• The controller de-energizes the compressor contactor (to
terminate pump down) 60 seconds later.
• If the condenser fan was ON, it will operate for 30 sec-
onds and then stop. If the condenser fan was OFF
(based on condensing pressure), it will remain OFF.
• The evaporator fans continue to operate.
Heat
• The electric heaters begin to pulse ON and OFF (ener-
gized and de-energized) when the Calculated Tempera-
ture Differential decreases to 0.6 C (1.0 F) below set-
point (on temperature pulldown). The amount of ON
time increases as the Calculated Temperature
Differential decreases below setpoint. The electric
heaters remain energized continuously (100% of time)
when the Calculated Temperature Differential decreases
to 3.1 C (5.5 F) below setpoint.
On temperature pull-up (and initial start-up), the con-
troller pulses the electric heaters ON and OFF until the
Calculated Temperature Differential increases to setpoint.
• The evaporator fans continue to operate.
• Controller turns OFF the In-range LED when supply air
temperature decreases more than 2.5 C (4.5 F) below set-
point. After the supply air temperature goes out-of-range
low, the In-range LED remains OFF until the supply air
temperature increases to 1.7 C (3.0 F) below setpoint.
NOTE: If the supply air sensor temperature goes
out-of-range low for 75 minutes after the unit is
In-range, the controller will turn ON the Alarm
Light. Alarm code 13 (a check alarm) is also
recorded in the controller’s memory.
Chill Load Control Sequence (Setpoints at -9.9 C
[14.1 F] and Above)
A. Cool
B. Modulation Cool
C. Null
D. Heat
E. In-Range
1. Decreasing Temperature
2. Setpoint
3. Increasing Temperature
4. Calculated Temperature Differential
5. Supply Air Temperature
Содержание CRR-20
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