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B. 579F240,300 Units (Fig. 42)

1. Shut off unit power supply.
2. Remove fan top-grille assembly and loosen fan hub

screws.

3. Adjust fan height on unit, using a straightedge

placed across the fan orifice.

4. Tighten setscrews and replace rubber hubcap to pre-

vent hub from rusting to motor shaft.

5. Fill hub recess with permagum if rubber hubcap is

missing.

VII. POWER FAILURE

Dampers have a spring return. In event of power failure,
dampers will return to fully closed position until power is
restored. Do not manually operate economizer motor.

VIII. REFRIGERANT CHARGE

Amount of refrigerant charge is listed on unit nameplate and
in Table 1. Refer to 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.

NOTE:

Do not use recycled refrigerant as it may contain

contaminants.

A. No Charge

Use standard evacuating techniques. After evacuating sys-
tem, weigh in the specified amount of refrigerant (refer to
Table 1).

B. Low Charge Cooling

Using cooling charging chart (see Fig. 43), add or remove
refrigerant until conditions of the chart are met. Note that
charging chart is different from those normally used. An
accurate pressure gage and temperature-sensing device is
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 ambient
temperature does not affect reading.

C. To Use the Cooling Charging Chart

Use the above temperature and pressure readings, and find
the intersection 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. Recheck 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 15 and 20 degrees of superheat at the compressors.
The valves are factory set and should not require
re-adjustment.

D. Perfect Humidity™ System Charging

The system charge for units with the Perfect Humidity
option is greater than that of the standard unit alone. The
charge for units with this option is indicated on the unit
nameplate drawing. To charge systems using the Perfect
Humidity dehumidification package, fully evacuate, recover,
and re-charge the system to the nameplate specified charge
level. To check or adjust refrigerant charge on systems using
the Perfect Humidity dehumidification package, charge per
the standard subcooling charts. The subcooler MUST be
deenergized to use the charging charts. The charts reference
a liquid pressure (psig) and temperature at a point between
the condenser coil and the subcooler coil. A tap is provided
on the unit to measure liquid pressure entering the sub-
cooler (leaving the condenser).

IX. GAS VALVE ADJUSTMENT

A. Natural Gas

The gas valve opens and closes in response to the thermostat
or limit control.

When power is supplied to valve terminals D1 and C2, the
main valve opens to its preset position.

The regular factory setting is stamped on the valve body
(3.3 in. wg).

To adjust regulator:

1. Set thermostat at setting for no call for heat.

2. Turn main gas valve to OFF position.

3. Remove

-in. pipe plug from manifold or gas valve

pressure tap connection. Install a suitable pressure-
measuring device.

NOTE: