4-12 Sequence of Operation µP-D Controller
CSR-20 & CSR-40, September 1999
Chill Loads Frozen Loads
Setpoints at -9.9 C Setpoints at -10.0 C
(14.4 F) and Above (14.0 F) and Below
Cool Mod Null Heat Defr Cool Null Defr Unit Function
•••• Evaporator Fans HIGH SPEED
1
•• Evaporator Fans LOW SPEED
1
••Evaporator Fans OFF
1
•••• Proportional-integral Derivative (Supply Air) Control
•• Return Air Sensor Control
••Evaporator Coil Sensor Control
•• • Compressor ON
•• • Compressor Liquid Injection ON (valve energized)
2
• Warm Gas Bypass Solenoid Valve OPEN (energized)
3
••• •• Condenser Fan ON
4
••Modulation Valve OPEN (de-energized)
5
•• • Modulation Valve MODULATING (energized)
5
•• •Electric Heaters ON (energized)
1
Return air temperature determines the evaporator fan speed (except when Economy Mode is ON):
• At return air temperatures of -9.9 C (14.4 F) and above, the evaporator fans operate on high speed.
• At return air temperatures of -10.0 C (14.0 F) and below, the evaporator fans operate on low speed.
2
Controller OPENS (energizes) the liquid injection valve:
• For 5 minutes whenever the compressor starts.
• Continuously when the unit is in Modulation Cool.
• Continuously when the unit is in Power Limit mode.
• When the compressor discharge temperature exceeds 138 C (280 F).
3
Controller OPENS (energizes) the warm gas bypass valve:
• When the calculated temperature differential is less than 0.6 C (1.0 F), the controller pulses the bypass valve OPEN and
closed. The amount of OPEN (energized) time increases as the modulation valve closes.
• When the modulation valve is closed (PCVAL = 100%), the bypass valve remains open (energized) continuously.
4
Condenser fan operation:
• Cooling Mode: Fan operation is impossible to determine exactly because the controller uses a control algorithm to cycle the
condenser fan between ON and OFF. However, the condenser fan will typically be ON when:
- The compressor discharge temperature is above 50 C (122 F) and increasing, or
- The condenser temperature is above 35 C (95F).
• Null Mode: If the condenser fan was ON when the unit shifted to NULL, it will operate for 30 seconds and stop.
• Water-cooled Condenser Option: When water supply pressure opens the water pressure switch, the controller stops the con-
denser fan.
NOTE: The condenser fan operates continuously if either the compressor or condenser temperature sen-
sor is defective.
5
Modulation valve MODULATES:
• When the Power Limit mode is ON.
• When the calculated temperature differential is less than 2.5 C (4.5 F) above setpoint.
Operating Mode Function Chart — Standard Operation
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