6
INSTALLATION cont.
low, there will be insufficient pressure to operate
the expansion valve properly. During low
ambient temperatures, it is difficult to start a
system because the refrigerant will migrate to the
cold part of the system (condenser) and make it
difficult for refrigerant to flow.
• The AAON 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 backs liquid
refrigerant up into the condenser reducing its
capacity that 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.
• There are different types of low ambient control
used. The following describe the different
systems. Inspect the unit to determine the system
used.
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 (180 psig for R-22 and 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.
Piping Schematic of Example system using the LAC valve.
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