Carrier 38AUM Series Installation, Operation & Maintenance Manual page 20

Fig: - Recommended Minimum Cool-Down Time After Compressor is Stopped
Start Unit
Set the space thermostat to a set point above space temperature so that there is no demand for cooling. Close
the 38AUM disconnect switch. Only the crankcase heater will be energized.
Reset the space thermostat below ambient so that a call for cooling is ensured.
Never charge liquid into the low-pressure side of system. Do not overcharge. During charging or removal of refrigerant,
be sure indoor-fan system is operating. Ensure both outdoor fan motors are running; bypass any Motormaster function.
Adjust Refrigerant Charge — Refer to Cooling Charging Charts. For applications with line lengths greater than 125 ft
(38 m), contact Carrier representative. Make sure that all condenser fans are operating, and on units with the HGBP
(hot pass bypass) option make sure that the HGBP solenoid valve is deactivated (see procedure below), before
adjusting charge to the charging charts. Vary refrigerant until the conditions of the chart are met. Note that the
charging charts are different from the type normally used. The charts are based on charging the units to the correct
subcooling for the various operating conditions. Accurate pressure gage and temperature sensing device are required.
Connect the pressure gage to the service port on the liquid line service valve. Mount the temperature sensing device
on the liquid line close to the liquid line service valve, and insulate it so that outdoor ambient temperature does not
affect the reading. Indoor airflow must be within the unit's normal operating range. Operate the unit for a minimum of
15 minutes. Ensure that pressure and temperature readings have stabilized. Plot the liquid pressure and temperature
on chart and add or reduce the charge to meet the curve. Adjust the charge to conform with the charging chart, using
the liquid pressure and temperature to read the chart.
Final Checks —
Ensure that all safety controls are operating, control panel covers are on, and the service panels are in place.
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment damage.
Using plotted operating point:
If plotted operating condition is -
BELOW the curve
ABOVE the curve
CAUTION
Adjust charge by -
REDUCE charge
ADD charge
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