AAON LC-054 - Manual (Page 20)

20
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.
Compressors
The scroll compressors are fully hermetic
and require no maintenance except keeping
the shell clean.
Refrigerant Filter Driers
Each refrigerant circuit contains a filter
drier. Replacement is recommended when
there is excessive pressure drop across the
assembly or moisture is indicated in a liquid
line sight glass.
Circuit Loading Max. Pressure Drop
100% 10 psig
50% 5 psig
Evaporator
The evaporators are direct expansion type
with a thermal expansion valve to regulate
refrigerant. Normally no maintenance or
service work will be required.
Adjusting Refrigerant Charge
All AAON chillers are shipped with a full
factory charge. Periodically additional
charge may be required.
Charging a system in the field must be based
on determination of liquid sub-cooling and
evaporator superheat. On a system with a
thermostatic expansion valve liquid sub-
cooling is more representative of the charge
than evaporator superheat but both
measurements must be taken.
Refer to the Unit Nameplate as a reference
when determining the proper refrigerant
charge.
Before Charging
Unit being charged must be at or near full
load conditions before adjusting the 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 2 when
determining the proper sub-cooling.
Measure the temperature of the liquid line as
it leaves the condenser coil.
Checking Liquid Sub-cooling
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.
Convert the pressure obtained to a saturated
temperature using the appropriate refrigerant
temperature-pressure chart.
Subtract the measured liquid line
temperature from the saturated temperature
to determine the liquid sub-cooling.
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