• Relay output SNF CYC= Cycle the refrigeration system ON and OFF at a rate equal to the
average rate of the last four ON or OFF cycles prior to the failure of the sensor. OFF periods
during defrost are not included in the average OFF times. In this mode, the ASD parameter is
observed during the OFF periods.
For more information about a relay output's ON and OFF state, see Relay outputs.
Condensing unit control system example
You can build a variety of different control systems with C450CCU condensing unit control module
and expansion modules. The following example provides information about the module assembly,
including wiring diagrams for system sensors and relay outputs.
Note: The physical configurations and wiring shown in the following example illustrate a typical
condensing unit control system application. Your control application may require less modules
if your application does not require two-speed evaporator fan control, active defrost, or a pump
down control. Passive, off-cycle defrost applications do not require a defrost termination sensor
or switch, Sn-2.
Control system example
The following figure shows an example of a condensing unit control system module assembly and
the user-installed field wiring for a cooling application with two-speed evaporator fan control, active
defrost, and pump down control.
Note: Connect cable shields at only one point to any C terminal on the input terminal block.
Figure 3: Typical condensing unit control system
Table 5: C450CCU condensing unit control system
Callout Description
1 A99 temperature sensor; Sn-1 space temperature sensor
2 A99 temperature sensor; Sn-2 defrost termination sensor
3 P499 or P599 pressure transducer; Sn-3 pressure monitoring and control
4 C450CCU condensing unit control module
5 C450YNN power module
6 C450SCN relay expansion module with two relay outputs
7 C450SBN relay expansion module with one relay output
8 Refrigeration or LLSV control circuit, OUTR1 (24 VAC to 240 VAC)
9 High-speed evaporator fan control circuit: optional OUTR2 (24 VAC to 240 VAC)
10 L1 and L2; 240 VAC supply power to power module
17System 450 Series C450CCU Condensing Unit Control System Technical Bulletin
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