Johnson Controls System 450 Series Technical Bulletin

An A99 sensor that connects to the Sn-1 and C terminals on the low-voltage input terminal block
on the C450CCU control module senses the refrigerated space temperature. Set up the Sn-1
refrigerated space temperature sensor in the control system UI.
An A99 sensor that connects to the Sn-2 and C terminals on the low-voltage input terminal block
on the C450CCU control module controls defrost cycle termination . Set up the Sn-2 defrost
termination sensor in the control system UI.
You can also control defrost cycle termination with a user-supplied evaporator temperature
switch that you connect to the Sn-2 and C terminals on the low-voltage input terminal block on the
C450CCU control module. For more information, see Defrost termination using a binary switch.
Medium temperature refrigeration applications that set up for passive, off-cycle defrost, do not
require a defrost termination sensor or switch.
Observe the following guidelines when you select, install, and set up the temperature and pressure
transducers for your control system:
• Wire the correct temperature sensors and correct pressure transducer to the correct input
terminals on the control module. For more information, see Wiring.
• Select the correct temperature sensor type, °C or °F, in the UI for each temperature sensor
that is wired to the control module. For more information, see Setting up the sensors and
transducers.
• Select one of the following pressure transducer types:
- None
- P100
- P110
- P200
- P8
- P15
For more information, see Setting up the sensors and transducers.
Defrost termination using a binary switch
You can set up Sn-2, the defrost termination sensor input, as a binary input sensor (bin) in the
condensing unit control module UI. You can then connect a dry-contact, evaporator temperature
switch to the Sn-2 and C input terminals, instead of an A99 temperature sensor to indicate defrost
termination on evaporator temperature rise. The evaporator temperature switch's preset close-on
rise temperature setpoint determines the defrost termination temperature.
Note: Make sure that the binary switch that connects to the Sn-2 is dry-contact and does not
provide any voltage to the input.
Relay outputs
Relay outputs provide low and line-voltage on and off control for the compressor or solenoid,
defrost heat source, and evaporator fan control. Each relay output is a single-pole, double-throw
(SPDT) set of Form-C dry contacts.
Note: Relay outputs are SPDT dry contact relays only and do not provide any power source for
controlled equipment.
Figure 1 shows a green LED on the control module housing that indicates the relay output status.
The following example is for a relay output that is configured to energize the relay when the output
status is ON.
System 450 Series C450CCU Condensing Unit Control System Technical Bulletin14

Johnson Controls System 450 Series Specifications

General

Brand	Johnson Controls
Model	System 450 Series
Category	Control Unit
Language	English