Carrier 48PG20-28 specifications Gas Valve Adjustment, Charging Chart 48PG20

Refrigerant Charge — Amount of refrigerant charge is 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

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 1/8-in. pipe plug from manifold or gas valve pressure tap connection. Install a suitable pressure- measuring device.

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