CRR-20 & CRR-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. The controller regu-
lates compressor operation based the return air sensor and set-
point temperatures to determine operating mode switch points.
At setpoints at -10 C (14 F) and below, 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 sen-
sor temperatures.
• Controller uses the condenser fan pressure switch input
to cycle a single-speed condenser fan between ON
(switch open) and OFF (switch closed). The controller
uses the compressor discharge and condenser coil tem-
peratures to cycle the condenser fan ON and OFF on unit
with customer configurations 5015 or 5016 loaded
(CRR-40-52 units).
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
goes 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 will turn ON the Alarm
LED. 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]). Setting is
adjustable from -10 to 0 C (-18 F to 0 F).
8. ECMAX (default setting is +1.0 C [+1.8 F]). Setting
is adjustable from +10 to 0 C (+18 F to 0 F).
Summary of Contents for CRR-20
Page 4: ......
