FloAire Modular Packaged Unit - Manual (Page 11)

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13. If the unit is a cooling only unit, adjust the air proving switch such that prevailing winds cannot
start the condensers without the blower operating. With the unit operating, turn the adjustment
screw clockwise until condensers stop operating. Then turn the adjustment screw
counterclockwise until condensers operate. Turn the screw one half turn more counterclockwise.
14. Refer to the MUA manual to complete the startup of the MUA unit.
Checking the Refrigerant Charge
Subcooling can still be used to identify an over or under-charged system. Typical systems will run
between 10F and 20F of subcooling. If lower than 10F, the system is likely undercharged. If over 20F, the
system is probably overcharged. These "rules of thumb" are approximate. For the condensers used on
this system, the appropriate subcooling is shown below: (First number in unit size is tonnage x 12)
Subcooling is desirable because it increases the efficiency of an air conditioning system. However, too
much subcooling will back liquid up in the condenser causing increased head pressures. This will cause
the system to operate inefficiently and in extreme cases may cause the compressor to trip on its high
pressure control or its internal protector.
In the example below, a standard gauge set is connected (blue to suction and red to liquid) to a system
operating on R410A refrigerant.
The liquid line saturation temperature is reading approximately 98°F from the gauge. The surface
temperature of the liquid line is reading 83.5°F. The surface temperature reflects the actual temperature
of the refrigerant. To calculate subcooling, subtract the surface temperature from the gauge temperature: