AAON LN-140 - Manual (Page 29)

29
Maintenance
General
Qualified technicians must perform routine
service checks and maintenance. This
includes
reading and recording the
condensing and suction pressures and
checking for normal sub-cooling and
superheat.
Air-cooled
condenser units require
maintenance schedules/procedures. Unit
specific instructions are included in this
manual.
Compressors
The scroll compressors are fully hermetic
and require no maintenance except keeping
the shell clean.
Adjusting Refrigerant Charge
All AAON chillers are shipped with a full
factory charge. Periodically adjusting the
charge of a system may be required.
Adjusting the charge of a system in the field
must be based on determination of liquid
sub-cooling and evaporator superheat. On a
system with an expansion valve liquid sub-
cooling is more representative of the charge
than
evaporator superheat but both
measurements must be taken.
Before Charging
Refer to the unit nameplate as a reference
when determining the proper refrigerant
charge.
Unit being charged must be at or near full
load conditions before adjusting the charge.
Units equipped with hot gas bypass must
have the hot gas bypass valve closed to get
the proper charge.
After adding or removing charge the system
must be allowed to stabilize, typically 10-15
minutes,
before making any other
adjustments.
The type of unit and options determine the
ranges for liquid sub-cooling and evaporator
superheat.
Refer to Table 6 when
determining the proper sub-cooling.
For units equipped with low ambient (0°F)
option see the special charging instructions
at the end of this section.
Checking Liquid Sub-cooling
Measure the temperature of the liquid line as
it leaves the condenser coil.
Read the gauge pressure at the liquid line
close to the point where the temperature was
taken. You must use liquid line pressure as it
will vary from discharge pressure due to
condenser coil pressure drop.
The Clean Air Act of 1990 bans the
intentional venting of refrigerant
(CFC’s and HCFC’s) as of July 1,
1992. Approved methods of recovery,
recycling or reclaiming must be
followed. Fines and/or incarceration
may be levied for non-compliance.
CAUTION
Polyolester (POE) and Polyvinylether
(PVE) oils are two types of lubricants
used in hydrofluorocarbon (HFC)
refrigeration systems. Refer to the
compressor label for the proper
compressor lubricant type.
CAUTION