CSR-20 & CSR-40, September 1999
µ
P-D Controller
Sequence of Operation
4-13
Continuous Temperature Control Operation
Chill Loads — Controller Setpoint at -9.9 C (14.1 F)
and Above
After the unit reaches setpoint on initial start-up operation, the
controller regulates the compressor, modulation valve and
electric heaters based on a CALCULATED TEMPERATURE
DIFFERENTIAL (see “General Theory of Operation” in this
chapter for more detail). This means the unit operating mode
can NOT be predicted based ONLY on the setpoint and supply
air sensor temperatures. The controller operates the unit on:
• Cool mode
• Modulation Cool mode
• Null mode
• Heat mode
• Defrost mode
• Evaporator fans operate on high speed (except when
Economy mode is ON and temperature is In-range) and
continuously circulate air inside the container (except
during defrost).
• Controller display shows the setpoint and supply air tem-
peratures.
• Controller uses a control algorithm to cycle the con-
denser fan between ON and OFF. Typically, the con-
denser fan will typically be ON when:
- the compressor temperature is above 50 C (122 F)
and increasing, or
- the condenser temperature is above 35 C (95F).
Cool
• Controller calls for the Cool mode whenever the
Calculated Temperature Differential is more than 2.5 C
(4.5 F) above setpoint.
• Modulation valve is fully open so the unit provides max-
imum cooling capacity.
• Power limit is active when the unit is operating in the
Cool mode.
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
Economy Mode ON: Evaporator Fans HIGH SPEED1
•
•
•
•
•
Economy Mode ON: Evaporator Fans LOW SPEED1
•
•
•
Economy Mode ON: Evaporator Fans OFF1
•
Dehumidify ON: Dehumidify Valve CLOSED (energized)2
•
Dehumidify ON: Electric Heaters ON (energized)2
•
•
•
•
Humidify ON: Air Compressor ON (energized)3
1Economy Mode ON: • On Chill Loads, the evaporator fans operate on low speed when the supply air temperature is In-range.
• On Frozen Loads, the evaporator fans stop during the Null mode when the return air temperature is In-
range. A timer re-starts the evaporator fans on low speed for 5 minutes every 45 minutes. If cooling is
required, the evaporator fans operate until the unit returns to Null mode.
2Dehumidification Option: When the Dehumidify Mode is set to ON, the supply air temperature must be in-range to CLOSE
(energize) the dehumidify valve:
• When the humidity is 1 to 5% above setpoint, the controller CLOSES (energizes) the dehumidify valve.
• When the humidity is more than 5% above setpoint, the controller CLOSES (energizes) the dehumidify valve AND pulses
the electric heaters ON and OFF.
3Humidification Option: When the container humidity is more than 2% below the humidity setpoint, the controller operates (ener-
gizes) the air compressor to inject atomized water directly into the evaporator supply air stream.
Operating Mode Function Chart — Optional Feature Operation
