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1.
The control board will de-energize the solenoid (suction or liquid) when a defrost
occurs while simultaneously energizing the relay controlling the defrost breakers.
2.
When the defrost relay is energized the POWERLINK™ breakers will receive a
momentary charge or pulse from a capacitor in its POWERLINK™ Power Supply
(PPS). The energized motor moves a push/pull rod similar to what might be found
in a manual switch. A slight delay between the control circuit demand and the
POWERLINK™ response will be noticed. This pulse switches the
POWERLINK™ such that the heaters are now energized. At the termination of
defrost, the PPS will receive another pulse, causing the POWERLINK™ to switch
off.
Offtime Defrost
Application
Offtime defrost is the simplest defrost type. A relay is used to de-energize a solenoid valve
at specific times. Suction stop solenoid valves should be used to control temperature on
long lineups due to the limited receiver capacity. Isolation ball valves for each case lineup
are recommended for ease of servicing.
Defrost Operation
1.
To initiate a defrost, the control board will de-energize the specific circuit solenoid.
2.
After the preset time for defrost has elapsed, the unit will energize the solenoid
allowing normal refrigeration.
Sensor Applications
Suction Pressure Sensor
This suction pressure input provides the electronic controller the necessary information to
cycle the compressors on and off to maintain an overall setpoint. You will need to program
the following: Setpoint, High Alarm, Low Alarm, Range.
The high and low alarm settings provide a window of safe operation that the Protocol™
should operate within. If the suction pressure moves outside this margin of operation for
more than 30 minutes, the control will default to switchback operation and control of the
compressors will be passed to a low pressure mechanical switch mounted inside the
Protocol™ cabinet.
Suction Pressure Input
This suction pressure input has a dual function. It can provide the electronic controller the
necessary information to cycle the compressors on and off under a split suction
configuration, or it can be used to monitor the discharge pressure. If the input is used to
monitor discharge pressure, you will need to program the following: High Alarm, Low
Alarm, and Range (typically 500 psi).
Protocol™ Installation and
106
Service Manual
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Table of Contents
Troubleshooting
