T-354 5–125.10.4 Sequence of Operation - DefrostThe defrost cycle may consist of up to three distinct operations. The first is de-icing of the coil, the second is aprobe check cycle, and the third is snap freeze.Defrost may be requested by any one of the following methods:The manual defrost function (also manual defrost switch function if equipped) is initiated and ended by the userusing the keypad or manual defrost switch (if equipped).NOTEThe Manual Defrost / Interval key can be used to initiate a manual defrost. Minimum Software releaseversion #5126 is required in order to use this function.Manual Defrost/Interval Key Operation:1. Depressing and holding the Manual Defrost/Interval Key for five seconds will initiate defrost. If the ManualDefrost/Interval Key is released in less than five seconds, defrost interval (code 27) shall be displayed.2. The user sends a defrost request by communications.3. The defrost interval timer (controller function code Cd27) reaches the defrost interval set by the user.4. The controller probe diagnostic logic determines that a probe check is necessary based on the temperaturevalues currently reported by the supply and re turn probes.5. The controller Demand Defrost configuration variable (CnF40) is set to “In” and the unit has been in pulldown operation for over 2.5 hours without reaching set point.Figure 5.8 DefrostThe processing of a defrost request is controlled by the defrost termination thermostat. The defrost terminationthermostat is not a physical component. It is a software point that acts as a thermostat, allowing defrost when it isconsidered “closed” and preventing or terminating defrost when it is considered “open”.CONTROL TRANSFORMERPOWER TOCONTROLLERSIGNAL TOCONTROLLERSIGNAL TOCONTROLLERENERGIZEDDE-ENERGIZEDFOR FULL DIAGRAM ANDLEGEND, SEE SECTION 7SIGNAL TOCONTROLLER
