8
Check Charge
Factory charge amount and desired subcooling are shown on unit
rating plate. Additional subcooling may be required to achieve
optimal heating performance based on the installed indoor unit.
(see Table 5).
Charging method is shown on information plate inside unit. For
TXV, use subcooling method. For piston, use superheat method.
To properly check or adjust charge, conditions must be favorable
for subcooling or superheat charging. Favorable conditions exist
when the outdoor temperature is between 70
_
F and 100
_
F
(21.11
_
C and 37.78
_
C), and the indoor temperature is between
70
_
F and 80
_
F (21.11
_
C and 26.67
_
C). Follow the procedure
below:
Unit is factory charged for 15ft (4.57 m) of lineset. Adjust charge
by adding or removing 0.6 oz/ft (.018 kg/m) of 3/8 liquid line
above or below 15ft (4.57 m) respectively.
For standard refrigerant line lengths (80 ft/24.38 m or less), allow
system to operate in cooling mode at least 15 minutes. If conditions
are favorable, check system charge by super heat method for fixed
metering device and subcooling method for TXV. If any
adjustment is necessary, adjust charge slowly and allow system to
operate for 15 minutes to stabilize before declaring a properly
charged system. Refer to Table 5 or 5 for additional subcooling
required.
If the indoor temperature is above 80
_
F (26.67
_
C), and the
outdoor temperature is in the favorable range, adjust system charge
by weight based on line length and allow the indoor temperature to
drop to 80
_
F (26.67
_
C) before attempting to check system charge
by subcooling method as described above.
If the indoor temperature is below 70
_
F (21.11
_
C), or the outdoor
temperature is not in the favorable range, adjust charge for line set
length above or below 15ft (4.57 m) only. Charge level should then
be appropriate for the system to achieve rated capacity. The charge
level could then be checked at another time when the both indoor
and outdoor temperatures are in a more favorable range.
NOTE
: If line length is beyond 80 ft (24.38 m) or greater than 20
ft (6.10 m) vertical separation, See Residential Piping and Long
Line Guideline for special charging requirements.
Units with Cooling Mode TXV
Units installed with cooling mode TXV require charging by the
subcooling method.
1. Operate unit a minimum of 10 minutes before checking
charge.
2. Measure liquid service valve pressure by attaching an accur-
ate gage to service port.
3. Measure liquid line temperature by attaching an accurate
thermistor type or electronic thermometer to liquid line near
outdoor coil.
4. Refer to unit rating plate for required subcooling temperat-
ure.
5. Refer to Table 6. Find the point where required subcooling
temperature intersects measured liquid service valve pres-
sure.
6. To obtain required subcooling temperature at a specific li-
quid line pressure, add refrigerant if liquid line temperature
is higher than indicated or reclaim refrigerant if temperature
is lower. Allow a tolerance of
3
_
F.
Heating Check Chart Procedure
To check system operation during heating cycle, refer to the
Heating Check Chart on outdoor unit. This chart indicates whether
a correct relationship exists between system operating pressure and
air temperature entering indoor and outdoor units. If pressure and
temperature do not match on chart, system refrigerant charge may
not be correct. Do not use chart to adjust refrigerant charge.
