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. CF Series
condensers and condensing units use an
LAC valve for low ambient operation.
LAC Valve
The Low Ambient Control (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 10 - Piping Schematic of Example System using the LAC Valve
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