AAON F-060 - Manual (Page 21)

21
Before Charging
The unit being charged must be at or near
full load conditions before adjusting the
charge.
Units equipped with hot gas reheat must
have the hot gas reheat valves closed to get
the proper charge.
Units equipped with hot gas reheat must be
charged with the hot gas valve closed while
the unit is in cooling mode.
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 7 when
determining the proper sub-cooling.
The vertical rise of the liquid line must be
known in order to adjust the sub-cooling
range for proper charge.
Checking Liquid Sub-cooling
1. Measure the temperature of the liquid
line as it leaves the condenser coil.
2. Read the gauge pressure reading of 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. 3. Convert the pressure obtained in Step 2 to
a saturated temperature using the
appropriate refrigerant temperature-pressure
chart.
4. Subtract the measured liquid line
temperature in Step 1 from the saturated
temperature in Step 3 to determine the liquid
sub-cooling.
5. Compare calculated sub-cooling to
TABLE 7 for the appropriate unit type and
options.
Checking Evaporator Superheat
1. Measure the temperature of the suction
line close to the compressor.
2. Read gauge pressure at the suction line
close to the compressor.
3. Convert the pressure obtained in Step 2 to
a saturated temperature using the
appropriate refrigerant temperature-pressure
chart.
4. Subtract the saturated temperature in Step
3 from the measured suction line
temperature in Step 1 to determine the
evaporator superheat.
5. Compare calculated superheat to TABLE
7 for the appropriate unit type and options.
Adjusting Sub-cooling and Superheat
Temperatures
The system is overcharged if:
1. the sub-cooling temperature is too high
and
2. the evaporator is fully loaded (low loads
on the evaporator result in increased sub-
cooling) and
3. the evaporator superheat is within the
temperature range as shown in TABLE 7
(high superheat results in increased sub-
cooling)
The Clean Air Act of 1990 bans the
intentional venting of refrigerant as of
July 1, 1992. Approved methods of
recovery, recycling, or reclaiming
must be followed.
CAUTION