Carrier 38GS - Manual (Page 12)

8. Add charge by slowly opening Chargemaster®
valve. If necessary, reduce charge by bleeding at
liquid line service valve. Check outdoor air and
evaporator temperature during procedure. If
they change, refer back to Chargemaster
Charging Chart for new value.
Correct use of Chargemaster ensures an opti­
mum refrigerant charge will be in system when
conditions and system components are normal.
However, the Chargemaster does not solve or fix
system abnormalities. It indicates correct charge
for condition of system. It will not make correc­
tions for dirty filters, slow fans, excessively long or
short suction lines or other abnormal conditions.
This charging device ensures that a correct relation­
ship exists between outdoor temperature, evap­
orator temperature, and suction line temperature
on a specific system.
Sight Glass Method — A satisfactory operating
charge can be obtained on thermal expansion valve
systems by charging to a clear sight glass. For
optimum charge, elevate high-side pressure to
380 ± 10 psig by blocking condenser fan discharge
or condenser entering air. Charge to a clear sight
glass while holding high-side pressure constant. For
peak efficiency, adjust charge to yield a liquid
refrigerant temperature at the evaporator that is
approximately the same as outdoor dry-bulb
temperature.
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