Application 4: Controlling the temperature of a walk-in
freezer
You can use the C450CCU to control the temperature of a walk-in freezer using one or two-speed
evaporator fans, electric defrost and pump down control
The following figure shows an active electric heat defrost control system that has the following
features:
• Low temperature
• Pump down control
Figure 12: Active electric heat defrost control system with pump down control
Table 19: C450CCU condensing unit control system
Callout Description
1 Sn-3 low-pressure pump down transducer. To control a compressor or compressor starter with low pressure,
connect a P499 or P599 pressure transducer to Sn-3, 5V, and C.
2 Sn-1 refrigerated space temperature sensor. To control the liquid line solenoid valve, connect an A99 Series
temperature sensor to Sn-1 and C on the input terminal block.
3 Sn-2 defrost termination temperature sensor or switch. To control the defrost heater, connect an A99 Series
temperature sensor or user-supplied temperature switch to Sn-2 and C on the input terminal block.
4 C450CCU condensing unit control module
5 C450YNN power module
6 C450SCN relay expansion module with two relay outputs
7 C450SCN relay expansion module with two relay outputs
8 OUTR1: Output relay 1 terminal block. Connects to and controls the liquid line solenoid valve based on the
temperature sensed at Sn-1, the refrigerated space temperature sensor.
9 OUTR2: Output relay 2 terminal block. Connects to and controls either a 1-speed evaporator fan or the high-
speed on a two-speed evaporator fan, based on the evaporator fan control selections you configure in the UI.
10 Power module line-voltage supply power terminals. Connect 120 VAC or 240 VAC power to the appropriate
terminals to provide power to the condensing unit control system.
11 OUTR3: Output relay 3 terminal block. Connects to and controls the low-speed on a two-speed evaporator fan.
You need a C450 expansion module to provide OUTR3.
System 450 Series C450CCU Condensing Unit Control System Technical Bulletin38
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