Low Ambient Thermostats; Hot Gas Bypass Operation - Trane RAUJ-C20 Installation, Operation And Maintenance Manual

prevent low oil viscosity and foaming during
compressor starts.
When the compressor starts, the sudden reduction in
crankcase pressure causes the liquid refrigerant to boil
rapidly causing the oil to foam. This condition could
damage compressor bearings due to reduced
lubrication and could cause compressor mechanical
failures.
When power has been "Off" for an extended period,
allow the crankcase heater to operate a minimum of 24
hours before starting the unit.

Low Ambient Thermostats

20 to 60 Ton Units
In addition to the low ambient dampers on 25, 30, 50 &
60 Ton units, a low ambient thermostat is installed to
further restrict the airflow across the condenser by
cycling the 2B3 condenser fan on 25 & 30 Ton units
plus 2B6 on 50 & 60 Ton units. The thermostat opens
SS-SVX11K-EN
when the ambient temperature reaches 30ºF and closes
at approximately 33ºF.

Hot Gas Bypass Operation

The HGBP valve regulates evaporator pressure by
opening as suction pressure decreases, to maintain a
desired minimum evaporating pressure regardless of a
decrease in evaporator external loading.
When the evaporator (suction) pressure is above the
valve's setpoint, it remains closed. As suction pressure
falls below the valve's setpoint, the valve begins to
open. The valve will continue to open at a rate
proportional to the suction pressure drop, thus
maintaining evaporator pressure.
Hot gas bypass valves are adjustable and should be set
to begin opening at approximately 100 psig suction
pressure and reach the full open position at 98 psig for
DX coil applications.
O O p p e e r r a a t t i i n n g g P P r r i i n n c c i i p p l l e e s s
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