York DM090 Installation Manual

Also see for PREDATOR DM 090: Installation manual Technical guide Installation manual Technical guide Installation instruction

Contents

127408-YIM-B-0606Unitary Products Group 41ECONOMIZER WITH POWER EXHAUST -A unit equipped with an economizer (single or dual enthalpy)and a power exhaust operates as specified above with oneaddition. The power exhaust motor is energized 45 secondsafter the actuator position exceeds the exhaust fan set pointon the economizer control. When the power exhaust is oper-ating, the second stage of mechanical cooling will not oper-ate. As always, the "R" to "G" connection provides minimumposition but does not provide power exhaust operation.MOTORIZED OUTDOOR AIR DAMPERS -This system operation is the same as the units with no out-door air options with one exception. When the "R" to "G" cir-cuit is complete, the motorized damper drives open to aposition set by the thumbwheel on the damper motor. Whenthe "R" to "G" circuit is opened, the damper spring returnsfully closed.COOLING OPERATION ERRORSEach cooling system is monitored for operation outside of theintended parameters. Errors are handled as described below.All system errors override minimum run times for compressors.HIGH-PRESSURE LIMIT SWITCHDuring cooling operation, if a high-pressure limit switchopens, the UCB will de-energize the associated compressor,initiate the ASCD (Anti-short cycle delay), and, if the othercompressor is idle, stop the condenser fans. If the call forcooling is still present at the conclusion of the ASCD, theUCB will re-energize the halted compressor.Should a high-pressure switch open three times within twohours of operation, the UCB will lock-out the associated com-pressor and flash a code (see Table 52). If the other com-pressor is inactive, the condenser fans will be de-energized.LOW-PRESSURE LIMIT SWITCHThe low-pressure limit switch is not monitored during the ini-tial 30 seconds of a cooling system's operation. For the fol-lowing 30 seconds, the UCB will monitor the low-pressureswitch to ensure it closes. If the low-pressure switch fails toclose after the 30-second monitoring phase, the UCB will de-energize the associated compressor, initiate the ASCD, and,if the other compressor is idle, stop the condenser fans.Once the low-pressure switch has been proven (closed dur-ing the 30-second monitor period described above), the UCBwill monitor the low-pressure limit switch for any openings. Ifthe low-pressure switch opens for greater than 5 seconds,the UCB will de-energize the associated compressor, initiatethe ASCD, and, if the other compressor is idle, stop the con-denser fans.If the call for cooling is still present at the conclusion of theASCD, the UCB will re-energize the halted compressor.Should a low-pressure switch open three times within onehour of operation, the UCB will lock-out the associated com-pressor and flash a code (Table 52). If the other compressoris inactive, the condenser fans will be de-energized.FREEZESTATDuring cooling operation, if a freezestat opens, the UCB willde-energize the associated compressor, initiate the ASCD,and, if the other compressor is idle, stop the condenser fans.If the call for cooling is still present at the conclusion of theASCD, the UCB will re-energize the halted compressor.Should a freezestat open three times within two hours ofoperation, the UCB will lock-out the associated compressorand flash a code (Table 52). 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 be