Operation
Low Ambient Operation
During low ambient operation, outside air temperature below 13ºC, the RTRM will cycle the compressor and outdoor fan motor "Off" for approximately three minutes after every 10 minutes of accumulated compressor run time. The supply fan motor (IDM) will continue to operate during this evaporator defrost cycle (EDC) and the compressor and outdoor fan will return to normal operation once the defrost cycle has terminated and the compressor "Off" time delay has been satisfied.
Cooling with an
Economizer
The economizer is utilized to control the zone temperature providing the outside air conditions are suitable.
Outside air is drawn into the unit through modulating dampers. When cooling is required and economizing is possible, the RTRM sends the cooling request to the unit economizer actuator (ECA) to open the economizer damper. The RTRM tries to cool the zone utilizing the economizer to slightly below the zone temperature setpoint. If the mixed air sensor (MAS) senses that the mixed air temperature is below 53ºF, the damper modulates toward the closed position. If the zone temperature continues to rise above the zone temperature setpoint controlband and the economizer damper is full open, the RTRM energizes the compressor contactor (CC1). If the zone temperature continues to rise above the zone temperature setpoint controlband and the economizer damper is fully open, the RTRM energizes the compressor contactor (CC2).
The ECA continues to modulate the economizer damper open/closed to keep the mixed air temperature that is calculated by the RTRM.
If economizing is not possible, the ECA drives the damper to the minimum position setpoint when the supply fan relay (F) is energized and allows mechanical cooling operation. When the unit is equipped with the optional fan failure switch, wired between terminals
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