Refrigerant Charge; Gas Valve Adjustment - Carrier SINGLE PACKAGE ROOFTOP UNITS 48PG20-28 Installation And Service Instructions Manual

Refrigerant Charge —
listed on unit nameplate. Refer to Carrier GTAC II; Module 5;
Charging, Recovery, Recycling, and Reclamation section for
charging methods and procedures. Unit panels must be in place
when unit is operating during charging procedure.
Puron® (R-410A) refrigerant cylinders contain a dip tube
which allows liquid refrigerant to flow from the cylinder in an
upright position. Charge units with cylinder in the upright
position and a commercial type metering device in the mani-
fold hose.
This system uses Puron refrigerant which has higher
pressures than R-22 and other refrigerants. No other refrig-
erant may be used in this system. Gage set, hoses, and
recovery system must be designed to handle Puron refrig-
erant. If unsure about equipment, consult the equipment
manufacturer.
NOTE: Do not use recycled refrigerant as it may contain
contaminants.
NO CHARGE — Use standard evacuating techniques. After
evacuating system, weigh in the specified amount of refriger-
ant (refer to unit nameplate).
LOW CHARGE COOLING — Using cooling charging chart
(see Fig. 37-39), add or remove refrigerant until conditions of
the chart are met. An accurate pressure gage and temperature-
sensing device are required. Charging is accomplished by
ensuring the proper amount of liquid subcooling. Measure
liquid line pressure at the liquid line service valve using pressure
gage. Connect temperature sensing device to the liquid line near
the liquid line service valve and insulate it so that outdoor ambi-
ent temperature does not affect reading.
TO USE THE COOLING CHARGING CHART — Use the
above temperature and pressure readings, and find the intersec-
tion point on the cooling charging chart. If intersection point on
chart is above line, add refrigerant. If intersection point on
chart is below line, carefully recover some of the charge. Re-
check suction pressure as charge is adjusted.
NOTE: Indoor-air cfm must be within normal operating range
of unit. All outdoor fans must be operating.
The TXV (thermostatic expansion valve) is set to maintain
between 10 and 15 degrees of superheat at the compressors.
The valves are factory set and cannot be adjusted. Do not use a
TXV designed for use with R-22 refrigerant.
PURON REFRIGERANT — Puron refrigerant operates at 50
to 70 percent higher pressures than R-22. Be sure that servicing
Fig. 37 — Charging Chart — 48PG20
Amount of refrigerant charge is
Fig. 38 — Charging Chart — 48PG24
Fig. 39 — Charging Chart — 48PG28
equipment and replacement components are designed to oper-
ate with Puron refrigerant. Do not mix with components that
have been used with other refrigerants. Puron refrigerant, as
with other HFCs, is only compatible with POE oils.
Recovery cylinder service pressure rating must be 400 psig.
Puron systems should be charged with liquid refrigerant. Use a
commercial-type metering device in the manifold hose. Mani-
fold sets should be 750 psig high-side and 200 psig low-side
with 520 psig low-side retard. Use hoses with 750 psig service
pressure rating. Leak detectors should be designed to detect
HFC refrigerant.

Gas Valve Adjustment

NATURAL GAS — The gas valve opens and closes in re-
sponse to the thermostat or limit control.
When power is supplied to valve terminals W2 (High Fire)
and C1, the main valve opens to its preset position.
The regular factory setting is stamped on the valve body.
The setting is 3.00 in. wg for vertical supply/discharge units.
The setting is 2.95 in. wg for horizontal supply/discharge units.
To adjust regulator:
1. Set unit at setting for no call for heat.
2. Turn main gas valve to OFF position.
3. Remove 1 / -in. pipe plug from manifold or gas valve
8
pressure tap connection. Install a suitable pressure-
measuring device.
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