CSR-20 & CSR-40, September 1999
µ
P-D Controller
Sequence of Operation
4-15
Frozen Loads — Controller Setpoint at -10 C (14 F)
and Below
At setpoints of -10 C (14 F) and below, the controller locks out
the Modulation Cool and Heat modes, and warm gas bypass
valve operation. The controller uses the return air temperature
and setpoint temperature to determine operating mode switch
points. The controller operates the unit on:
• Cool mode
• Null mode
• Defrost mode
• Evaporator fans operate on low speed (after return air
temperature decreases to -10 C [14 F]) and continuously
circulate air inside the container (except during defrost;
or during Null mode with Economy Mode ON).
• Controller display shows the setpoint and return 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 return
air temperature is more than 1.0 C (1.8 F) above setpoint.
• Power limit is active when the unit is operating in the
Cool mode.
• After the initial temperature pull-down, the In-range
LED turns OFF if the return air temperature increases
more than 2.5 C (4.5 F) above setpoint. The return air
temperature must decrease to 1.7 C (3.0 F) above setpoint
to turn the In-range LED ON again.
NOTE: If the return air sensor temperature goes
out-of-range high for 75 minutes after the unit is
In-range, the controller turns ON the Alarm Light.
Alarm code 12 (a check alarm) is also recorded
in the controller’s memory.
Frozen Load Control Sequence (Setpoints at -10 C
[14 F] and Below) — Economy Mode OFF
A. Cool
C. Null
E. In-Range
1. Decreasing Temperature
2. Setpoint
3. Increasing Temperature
6. Return Air Temperature
Frozen Load Control Sequence (Setpoints at -10 C
[14 F] and Below) — Economy Mode ON
A. Cool
C. Null
E. In-Range
1. Decreasing Temperature
2. Setpoint
3. Increasing Temperature
6. Return Air Temperature
7. ECMIN (default setting is 2.0 C [3.6 F] below set-
point). Setting is adjustable from 0 to 10 C (0 F to 18
F) below setpoint.
8. ECMAX (default setting is 1.0 C [1.8 F] above set-
point). Setting is adjustable from 0 to 10 C (0 F to 18
F) above setpoint.
