Emerson E2 operation manual Clean and Door Switches

will turn the Defrost output ON to activate the heaters con- nected to the output.

Any user-defined Pump Down and Run-Off times will be observed as normal.

11.3.2.3Defrost Termination

Both the start and the end times of a defrost cycle are determined by the user. The Pump Down, Defrost, and Run-Off stages all have fixed durations, and when the last stage of the cycle is complete, defrost is terminated.

However, a Standard Circuit application may be pro- grammed to terminate the Defrost stage of the defrost cycle early if the temperature inside the case rises above a fail-safe temperature setpoint (called the termination set- point). For certain defrost types, defrost heat may also be “pulsed” in order to keep the temperature below the set- point without terminating defrost.

Pulsed Defrost

Figure 11-4- Defrost Termination (Pulsed)

Pulsed Defrost is only available if the circuit is using heated defrost, such as Electric or Hot Gas defrost.

Pulsed Defrost is similar to the Temperature Termina- tion strategy outlined in Section 11.3.2.3, except a defrost cycle always continues for the full programmed duration.

When the termination temperature rises above the set- point, defrost does not end. Instead, the defrost heat is turned OFF until the case temperature falls below the set- point, at which time the output will come back ON to con- tinue heating.

Figure 11-4illustrates what happens in a pulsed defrost cycle. In this example, the case reaches its termina- tion temperature approximately 2/3 of the way into its defrost cycle. Defrost continues, but defrost heat is turned

OFF until the temperature falls below the setpoint, at which point the heat is turned back ON.

Defrost heat will continue to be pulsed in this manner until the defrost time has passed. The defrost cycle will then begin the Run-Off period, and then restart refrigera- tion.

11.3.2.4Emergency Defrost

When necessary, a user can initiate an emergency defrost cycle in a circuit. Emergency defrost cycles are similar to normal defrost cycles, except an emergency defrost cycle will ignore all calls for termination and remain in defrost for the entire programmed defrost time. For cases using a pulsed defrost strategy, this means the defrost heat will not be pulsed during emergency defrost.

Emergency defrosts are initiated by the user from the Standard Circuit Bypass screen (see Section 12.6, Manual Defrost and Clean Mode).

11.3.2.5Hot Gas Defrost with ESR8 and MultiFlex ESR

If an ESR8 or MultiFlex ESR is used on a circuit that uses hot gas defrost, values for circuits in defrost are forced OPEN (100%) to allow hot gas to flow through the evaporators.

11.3.3 Clean and Door Switches

11.3.3.1Clean Switches

A Standard Circuit application may be configured to entirely shut down a case circuit so that it may be cleaned or serviced. A case circuit enters clean mode when it receives a signal from an input called the clean switch.

Clean switches may be set up as either “Switched” or “Timed.” If a clean switch is configured as “switched,” the circuit enters clean mode when the switch is turned ON, and it remains in clean mode until the switch is turned OFF. If a clean switch is configured as “timed,” the circuit enters clean mode when the switch is turned ON, and it remains in clean mode for a fixed user-defined amount of time.

During clean mode, the Fan, Defrost, and Refrigera- tion Solenoid outputs are all turned OFF, and the liquid line solenoid is CLOSED.

If desired, a notice may be sent to the E2’s Alarm Log so that the E2 can keep track of clean modes and times.

11.3.3.2Door Switches

Walk-In Box freezers are often equipped with door switches that disable the evaporators when the door is open. The E2 is capable of reading a digital door switch input and controlling the freezer appropriately.

When a door switch opens, the E2 will shut off the

Standard Circuits Software Overview • 11-7