21
Fig. 21. Advanced Scroll Temperature Protection (ASTP) is a
form of internal discharge temperature protection, that unloads
the scroll compressor when the internal temperature reaches
approximately 149°C (300°F). At this temperature, an internal
bi-metal disk valve opens and causes the scroll elements to
separate, which stops compression. Suction and discharge
pressures balance while the motor continues to run. The longer
the compressor runs unloaded, the longer it must cool before
the bi-metal disk resets. See Fig. 22.
To manually reset ASTP, the compressor should be stopped and
allowed to cool. If the compressor is not stopped, the motor will
run until the motor protector trips, which occurs up to 90 minutes
later. Advanced Scroll Temperature Protection will reset automati-
cally before the motor protector resets, which may take up to
2 hours.
Fig. 21 — Advanced Scroll Temperature Protection
Label
Fig. 22 — 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 38AU disconnect
switch. Only the crankcase heater will be energized.
Reset the space thermostat below ambient so that a call for cooling
is ensured.
ADJUST REFRIGERANT CHARGE
Refer to Cooling Charging Charts, Fig. 24-28. For applications
with line lengths greater than 125 ft (38 m), contact Carrier repre-
sentative. Make sure that all condenser fans are operating 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 operat-
ing conditions. Accurate pressure gauge and temperature sensing
device are required. Connect the pressure gauge to the service port
on the liquid line service valve. Mount the temperature sensing de-
vice on the liquid line close to the liquid line service valve, and in-
sulate 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. see Table 15. Adjust the charge to conform with
the charging chart, using the liquid pressure and temperature to
read the chart.
Table 15 — Using Plotted Operating Point
38AUZ*25 CHECK COMPRESSOR OIL LEVEL
After adjusting the refrigerant charge, allow the unit to run fully
loaded for 20 minutes. Stop the compressors and check the oil lev-
el. Oil level should be 1/3 to 1/2 up on the sight glass (see Fig. 23).
Fig. 23 — Recommended Oil Level — 38AUZ*25
Add oil only if necessary to bring the oil into view in the sight
glass. If oil is added, run the circuit for an additional 10 minutes,
then stop and check oil level. If the level remains low, check the
piping system for proper design for oil return; also, check the sys-
tem for leaks. If checking the oil level with unit running in part
load, let unit run one hour, then run at full load for 10 minutes. If
oil does not return to acceptable sight glass levels, check for cor-
rect suction piping and line sizing.
FINAL CHECKS
Ensure that all safety controls are operating, control panel covers
are on, and the service panels are in place.
1. Third-part trademarks and logos are the property of their respective
owners.
0
10
20
30
40
50
60
70
80
90
100
110
120
0 10203040 6070809050
Compressor Unloaded Run Time (Minutes)*
NOTES:
1 . Various factors, including high humidity, high ambient temperature,
and the presence of a sound blanket will increase cool-down times.
*Times are approximate.
Recommended Cooling Time*
(Minutes)
CAUTION
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment
damage.
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.
IF PLOTTED OPERATING
CONDITION IS
ADJUST CHARGE BY
BELOW the curve REDUCE charge
ABOVE the curve ADD charge
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