AAON RN-140 - Manual (Page 76)

76
Before Charging
Unit being charged must be at or near full
load conditions before adjusting the charge.
Units equipped with hot gas reheat must be
charged with the hot gas reheat valves
closed while the unit is in cooling mode to
get the proper charge. After charging, unit
should
be operated in reheat
(dehumidification) mode to check for
correct operation.
Units equipped with heat pump options
should be charged in heating mode to get the
proper charge. After charging, unit should
be operated in cooling mode to check for
correct charge. Charge may need to be
adjusted for cooling mode. If adjustments
are made in the cooling mode heating mode
must be rerun to verify proper operation.
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 the table below when
determining the proper sub-cooling.
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.
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.
Compare calculated sub-cooling to the table
below for the appropriate unit type and
options.
Checking Evaporator Superheat
Measure the temperature of the suction line
close to the compressor.
Read gauge pressure at the suction line close
to the compressor.
Convert the pressure obtained to a saturated
temperature using the appropriate refrigerant
temperature-pressure chart.
Subtract the saturated temperature from the
measured suction line temperature to
determine the evaporator superheat.
Compare calculated superheat to the table
below for the appropriate unit type and
options.
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