York Predator MagnaDRY DR090 Series Installation Manual

Also see for PREDATOR MagnaDRY DR090: Technical guide Installation manual

264276-XIM-B-120838 Johnson Controls Unitary ProductsShould a freezestat open three times within two hours ofoperation, the UCB will lock-out the associated compressorand flash a code (Table 34). If the other compressor is inac-tive, the condenser fans will be de-energized.LOW AMBIENT COOLINGTo determine when to operate in low ambient mode, the UCBhas a pair of terminals connected to a temperature-activatedswitch set at 45ºF. When the low ambient switch is closedand the thermostat is calling for cooling, the UCB will operatein the low ambient mode.Low ambient mode operates the compressors in this manner:10 minutes on, 5 minutes off. The indoor blower is operatedthroughout the cycle. The 5-minute off period is necessary todefrost the indoor coil.Low ambient mode always begins with compressor opera-tion. Compressor minimum run time may extend the minutesof compressor operation. The defrost cycle will begin immedi-ately following the elapse of the minimum run time.When operating in low ambient mode, the UCB will not lock-out the compressors due to a freezestat trip. However, afreezestat trip will de-energize the associated compressor. Ifthe call for cooling is still present at the end of the ASCD andthe freezestat has closed, the unit will resume operation.SAFETY CONTROLSThe unit control board monitors the following inputs for eachcooling system:1. A suction line freezestat to protect against low evapora-tor temperatures due to a low airflow or a low return airtemperature, (opens at 26 ± 5 °F and resets at 38 ± 5°F).2. A high-pressure switch to protect against excessive dis-charge pressures due to a blocked condenser coil or acondenser motor failure, (opens at 405 ± 10 psig or 440± 10 psig depending on unit model).3. A low-pressure switch to protect against loss of refriger-ant charge, (opens at 22 ± 5 psig or 45 ± 5 psig).The above pressure switches are hard-soldered to the unit.The refrigeration systems are independently monitored andcontrolled. On any fault, only the associated system will beaffected by any safety/preventive action. The other refrigerantsystem will continue in operation unless it is affected by thefault as well.The unit control board monitors the temperature limit switchof electric heat units and the temperature limit switch and thegas valve of gas furnace units.COMPRESSOR PROTECTIONIn addition to the external pressure switches, the compressorsalso have inherent (internal) protection. If there is an abnormaltemperature rise in a compressor, the protector will open to shutdown the compressor. The UCB incorporates features to mini-mize compressor wear and damage. An Anti-Short CycleDelay (ASCD) is utilized to prevent operation of a compressortoo soon after its previous run. Additionally, a minimum run timeis imposed any time a compressor is energized.The ASCD is initiated on unit start-up and on any compressorreset or lock-out.FLASH CODESThe UCB will initiate a flash code associated with errorswithin the system. Refer to UNIT CONTROL BOARD FLASHCODES Table 34.RESETRemove the call for cooling, by raising thermostat settinghigher than the conditioned space temperature. This resetsany pressure or freezestat flash codes.REHEAT MODE SEQUENCE OF OPERATIONThe reheat control board allows the user to select two differ-ent modes of operation via a jumper connection on the board.(See Figure 3.) Each mode is described below. Refer to Fig-ures 3 and 4 when reading this section.“NORMAL” MODEWhen the reheat control board (RCB) detects a need fordehumidification (24VAC) at "HUM" via the field supplieddehumidistat connected to RHTB-1 and RHTB-2 and there isnot a call for cooling, it energizes the hot gas relay (HGR),which energizes the 3-way valve (SOL 3), the condenser coilvalve (SOL 2), and de-energizes the reheat coil bleed valve(SOL 1). The Y1 signal is passed to the unit control board(UCB), which engages circuit # 1, resulting in circuit #1reheat mode operation.When the room thermostat calls for first stage cooling, with orwithout a call for dehumidification, the RCB senses a signalthrough "Y1", de-energizing the HGR, which de-energizesSOL 3 and SOL 2 and energizes SOL 1, engaging circuit #1,resulting in circuit #1 cooling mode operation.When the room thermostat calls for second stage cooling, theRCB senses a signal through "Y1" & "Y2" and engages circuit#1 and circuit #2 in cooling mode.Indoor blower operation is initiated upon a call for first stagecooling, second stage cooling or dehumidification.