York DC SERIES Installation Manual

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York DC SERIES Installation Manual Manual pdf 50 page image

5120410-XIM-B-021650 Johnson Controls Unitary ProductsWhen operating in low ambient mode, an evaporator low limitsensor (EC1, 2) temperature below 26ºF will de-energize theassociated compressor. If the call for cooling is still present atthe end of the ASCD and the and the evaporator temperaturesensor (EC1, 2) temperature is above 26°F, the unit will resumeoperation.Safety ControlsThe unit control board monitors the following inputs for eachcooling system:1. An evaporator low limit sensor (EC1, 2) (Located on theSuction Line at the Evaporator Coil.) to protect against lowevaporator temperatures due to a low airflow or a lowreturn air temperature, set at 26°F.2. A high-pressure switch to protect against excessivedischarge pressures due to a blocked condenser coil or acondenser motor failure, (opens at 625 ± 25 psig).3. A low-pressure switch to protect against loss of refrigerantcharge, (opens at 50 ± 5 psig).The above pressure switches are hard-soldered to the unit. Therefrigeration 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 switch ofelectric heat units and the temperature limit switch and the gasvalve 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 tominimize 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.ResetRemove the call for cooling, by raising thermostat setting higherthan the conditioned space temperature.Electric Heating Sequence Of OperationsThe following sequence describes the operation of the electricheat section.Two-stage heating:a. Upon a call for first stage heat by the thermostat, theheater relay (RW1) will be energized. After completingthe specified fan on delay for heating, the UCB willenergize the blower motor. If the second stage of heat isrequired, heater relay (RW2) will be energized. Aftercompleting the specified fan on delay for heating, theUCB will energize the blower motor.b The thermostat will cycle the electric heat to satisfy theheating requirements of the conditioned space.Electric Heat Operation ErrorsTemperature LimitIf the UCB senses zero volts from the high temperature limit,the indoor blower motor is immediately energized.This limit is monitored regardless of unit operation status, i.e.the limit is monitored at all times.If the temperature limit opens three times within one hour, it willlock-on the indoor blower motor.Safety ControlsThe UCB monitors the temperature limit switch of electric heatunits.The control circuit includes the following safety controls:Limit Switch (Ls)This control is located inside the heater compartment and is setto open at the temperature indicated in the Electric Heat LimitSetting Table 30. It resets automatically. The limit switchoperates when a high temperature condition, caused byinadequate supply air flow occurs, thus shutting down theheater and energizing the blower.ResetRemove the call for heating by lowering the thermostat settinglower than the conditioned space temperature.Electric Heat Anticipator SetpointsIt is important that the anticipator setpoint be correct. Too highof a setting will result in longer heat cycles and a greatertemperature swing in the conditioned space. Reducing thevalue below the correct setpoint will give shorter “ON” cyclesand may result in the lowering of the temperature within theconditioned space. Refer to Table 32 for the required electricheat anticipator setting.Table 31: Electric Heat Limit SettingUNIT (TONS) VOLTAGE HEATERkWLIMIT SWITCHOPENS °F10, 12.5380/41518 15010, 12.5 24 15010, 12.5 34 15010, 12.5 54 130