AAON LC-054 - Manual (Page 17)

17
The AAON low ambient (condenser flood-
back) system is used to operate a refrigerant
system below 25°F outside air temperature.
As the ambient temperature drops, the
condenser becomes more effective therefore
lowering the head pressure.
The low ambient system maintains normal
head pressure during periods of low ambient
by restricting liquid flow from the condenser
to the receiver, and at the same time
bypassing hot gas around the condenser to
the inlet of the receiver. This reduces liquid
refrigerant flow from the condenser,
reducing its effective surface area, which in
turn increases the condensing pressure. At
the same time the bypassed hot gas raises
liquid pressure in the receiver, allowing the
system to operate properly. LC Series
chillers use an LAC valve for low ambient
operation.
LAC Valve
The LAC valve is a non-adjustable three way valve that modulates to maintain receiver pressure.
As the receiver pressure drops below the valve setting (295 psig for R-410A), the valve
modulates to bypass discharge gas around the condenser. The discharge gas warms the liquid in
the receiver and raises the pressure to the valve setting. The following schematic shows an
example system using the LAC valve.
Figure 2 - Piping Schematic of Example System using the LAC Valve