Technical Service Bulletin

For most applications control is by the standard refrigeration "pump down" approach. The condensing unit is equipped with an adjustable pressure switch that is set for 25 lbs cut in (turn on) with a 20 lb differential (turn off). Standard equipment setup provided by USCS on the condensing unit will be used. This includes: Sight glass, receiver, liquid line filter and pressure switch. The DC-2 controller then controls the 115vac solenoid valve and fan in the evaporator.

While the system is running the pressure and temperatures will be within range. Once the minimum temperature setting is reached, the liquid line solenoid valve will close and the fan will turn off. After the refrigerant in the evaporator boils off, the suction pressure will be begin to "pump down". This will cause the suction pressure to decrease to the cut out point on the low pressure switch at the condensing unit, it will then turn off or shut down. When the room temperature rises above the set pint the solenoi valve opens, the fan turns on and the coil is again flooded with refrigerant, the pressure rises above the cut in point and the sytem start back on-line. The control system is designed to keep the liquid line solenoid (and therefore the compressor) from cycling within 10 minutes. This is to keep the system from short cycling. There is no wired connection between the condensing unit and the thermostat.

For long runs(+50') or installation of the condensing unit in areas that can see large swings of temperature it is recommended that a LAK and an accumulator be added by the installer for system reliability. Please see "TBS: Line Set Recommendations" for more details on planning Line Sets.

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