5–9 T-3545.10 SEQUENCE OF OPERATIONGeneral operation sequences for cooling, heating, and defrost are provided in the following sub-paragraphs. Sche-matic representation of controller action are provided in Figure 5.3 and Figure 5.4. Refer to Section 4 for detaileddescriptions of special events and timers that are incorporated by the controller in specific modes of operation.5.10.1 Sequence of Operation - Perishable Mode CoolingNOTEIn the conventional Perishable Mode of Operation, the evaporator motors run in high speed. In theeconomy Perishable Mode, the fan speed is varied.NOTEIn low temperature ambients, the condenser fan will be cycled by the controller to maintain proper con-densing pressure.1. With supply air temperature above set point and de creasing, the unit will be cooling with the condenser fanmotor (CF), compressor motor (CH), evaporator fan motors (EF) energized, and the COOL light illuminated(see Figure 5.5).Figure 5.5 Perishable Mode Cooling2. When the air temperature decreases to a predetermined tolerance above set point, the in-range light is illu-minated.3. As the air temperature continues to fall, modulating cooling starts at approximately 2.5C (4.5F) above setpoint (see Figure 5.3).4. The controller monitors the supply air. Once the sup ply air falls below set point and 0% SMV position isreached, the controller periodically records the sup ply air temperature, set point, and time. A calculation isthen performed by subtracting the set point reading from the supply air and multiplying the result by the timereading. The result is negative number.CONTROL TRANSFORMERPOWER TOCONTROLLERSIGNAL TOCONTROLLERSIGNAL TOCONTROLLERENERGIZEDDE--ENERGIZEDFOR FULL DIAGRAM ANDLEGEND, SEE SECTION 7NOTE: HIGH SPEED EVAPORATOR FAN SHOWN. FOR LOW SPEEDCONTACT TE IS DE-ENERGIZED AND CONTACT TV IS ENERGIZED
