Emerson E2 EEPRs Suction Stepper, Thermostatic Expansion Valves TXVs, Off Cycle Timed

time, Superheat Control will begin.

Recovery Mode always lasts for a specific number of seconds. The case controller determines the duration based on past performance of the evaporator during previous Recovery Modes.

Thermostatic Expansion Valves (TXVs)

As an alternative to regulating superheat using EEVs, case controllers also support cases that use mechanical thermostatic expansion valves (TXVs). When TXVs are being used, the case controllers use only Temperature Control to turn refrigeration ON and OFF. Superheat Control is disabled, since it is assumed the TXV is tak- ing care of the superheat.

11.4.3.2EEPRs (Suction Stepper)

The CC-100H, CS-100, and CCB (suction stepper and lineup) control case temperature from the suction side of the evaporator by using an EEPR to regulate suction pres- sure.

Suction-side control differs from liquid-side control in that Superheat Control is not used. In liquid-side control, the valve aperture is controlled in order to achieve a super- heat setpoint. In suction-side control, the CC-100 changes the valve aperture to achieve the case temperature set- point.

Case temperature may be supplied by a supply air sen- sor, return air sensor, or a mixture of the two values.

Temperature Control uses PID control to operate the valve and keep the case temperature input value equal to the case temperature setpoint.

Recovery Mode

Recovery Mode for suction-side case controllers is slightly different than Recovery Mode for liquid-side controllers. Suction-side case controllers enter Recovery Mode only after a defrost or cleaning cycle, and it does so in order to bring the case temperature down to a level that is controllable by Temperature Control.

During Recovery Mode, the valve is opened to a fixed percentage until the case temperature falls below the case setpoint. When this occurs, the case controller exits Recovery Mode and begins normal Temperature Con- trol.

11.4.4Defrost Control

The physical aspects of defrost control, such as shut- ting off valves and turning on defrost heat sources, is han- dled by the case controller. When operating on its own, a case controller initiates defrost cycles at programmed time intervals. When connected to a Case Circuit application, the case controllers’ defrost times are coordinated and scheduled by the E2.

11.4.4.1Defrost States

The defrost cycle for a Case Circuit application con- sists of three steps. Of these three, steps #1 and #3 apply only to cases with heated defrosts:

1.Pump Down - The defrost cycle begins with this step immediately after the refrigeration solenoid is turned OFF. During the Pump Down phase, the application waits for a user-specific amount of time to elapse before turning on the defrost heat. This allows refrigerant in the evaporator to be evacuated before defrost heat is activated. The compressor(s) remain ON during Pump Down.

Pump Down times may only be used for hot gas and electric type defrosts.

2.Defrost - During the defrost phase, refrigeration is disabled. If using electric defrost heaters will be ON. If using hot gas, heated refrigerant will be pumped through the coil. This phase will con- tinue until the defrost is terminated (see Section 11.3.2.3 for information on how defrost is termi- nated).

3.Run-Off - After defrost heat is deactivated, the application waits for the Run-Off time to pass before re-entering refrigeration mode. This allows melted frost on the evaporator to drain from the coil so that it will not re-freeze when refrigeration begins again. After the user-speci- fied Run-Off time has passed, the defrost cycle has ended.

Run-Off times may only be programmed for hot gas and electric type defrosts.

11.4.4.2 Defrost Types

There are many different ways used to defrost a refrig- erated case. A case controller is capable of using three dif- ferent types of defrost.

Off Cycle (Timed)

Off Cycle defrost (also known as Timed defrost) is simply a period of time during which refrigeration is sus- pended. No heat is applied to the evaporator. The applica- tion simply turns refrigerant flow OFF for the duration of the defrost cycle.

When these defrost types are used, Pump Down and Run-Off times are not necessary; therefore, they will not be part of the defrost cycle.

Hot Gas and Reversed Cycle Hot Gas

Hot Gas and Reversed Cycle Hot Gas require the use of hot gas from the refrigeration lines. During these types of defrost, the application will open the valve and pump heated refrigerant through the evaporator coil. Any user-

11-12 • E2 RX/BX/CX I&O Manual 026-1614 Rev 4 5-JAN-2013