Installation Operation Maintenance

OperationLow Ambient OperationDuring low ambient operation,outside air temperature below 13ºC,the RTRM will cycle the compressorand outdoor fan motor "Off" forapproximately three minutes afterevery 10 minutes of accumulatedcompressor run time. The supplyfan motor (IDM) will continue tooperate during this evaporatordefrost cycle (EDC) and thecompressor and outdoor fan willreturn to normal operation once thedefrost cycle has terminated andthe compressor "Off" time delay hasbeen satisfied.Cooling with anEconomizerThe economizer is utilized to controlthe zone temperature providing theoutside air conditions are suitable.Outside air is drawn into the unitthrough modulating dampers. Whencooling is required and economizingis possible, the RTRM sends thecooling request to the uniteconomizer actuator (ECA) to openthe economizer damper. The RTRMtries to cool the zone utilizing theeconomizer to slightly below thezone temperature setpoint. If themixed air sensor (MAS) senses thatthe mixed air temperature is below53ºF, the damper modulates towardthe closed position. If the zonetemperature continues to rise abovethe zone temperature setpointcontrolband and the economizerdamper is full open, the RTRMenergizes the compressor contactor(CC1). If the zone temperaturecontinues to rise above the zonetemperature setpoint controlbandand the economizer damper is fullyopen, the RTRM energizes thecompressor contactor (CC2).The ECA continues to modulate theeconomizer damper open/closed tokeep the mixed air temperature thatis calculated by the RTRM.If economizing is not possible, theECA drives the damper to theminimum position setpoint whenthe supply fan relay (F) is energizedand allows mechanical coolingoperation. When the unit isequipped with the optional fanfailure switch, wired betweenterminals J7-5 and J7-6 on theRTOM, the RTRM will stop allcooling functions and produce ananalog output if the fan failureswitch (FFS) does not open within40 seconds after a request for fanoperation. When the system isconnected to a remote panel, the"SERVICE" LED will flash when thisfailure occurs.RT-SVX20B-E457