AAON LL-540 - Manual (Page 31)

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Figure 10 - Incorrect Vent Pipe Connection
Stop bead on male end must be pushed
directly against the flared end of the female
end. When checking the inside of the joint,
the gasket is fully covered and out of sight.
Boiler Intake Connection
Remove the intake shipping cover. The
round collar on the back of the intake vent
passes through the cabinet wall and slides
over the crimped end of the air intake pipe
inside the unit. This joint should be secured
with aluminum foil tape. The outer flange of
the wall vent is fastened to the outer wall of
the cabinet using sheet metal screws.
Mounting Isolation
For roof mounted applications or anytime
vibration transmission is a factor, vibration
isolators may be used.
Access Doors
Lockable access door is provided to the
compressor and control compartment. A
separate access door is also provided to the
evaporator
and pumping package
compartment.
A light switch is provided on the wall of the
compressor and control compartment.
Low Ambient Operation
If the chiller is ordered with the Low
Ambient feature, the liquid system must use
a glycol solution and the piping must be
insulated to be prepared for freezing
conditions. Care must be taken in the source
of electrical power for the heating tape and
thermostat.
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. When the head
pressure gets too 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 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