21
ADVANCED SCROLL TEMPERATURE PROTECTION
(ASTP)
A label located above the terminal box identifies Copeland
1
Scroll compressor models that contain this technology. See
Fig. 20. Advanced Scroll Temperature Protection (ASTP) is a
form of internal discharge temperature protection, that unloads
the scroll compressor when the internal temperature reaches ap-
proximately 149°C (300°F). At this temperature, an internal bi-
metal disk valve opens and causes the scroll elements to sepa-
rate, which stops compression. Suction and discharge pressures
balance while the motor continues to run. The longer the com-
pressor runs unloaded, the longer it must cool before the bi-met-
al disk resets. See Fig. 21.
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. 20 — Advanced Scroll Temperature Protection
Label
Fig. 21 — 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. 22-29. Vary refrigerant un-
til 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 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 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 18. Adjust the charge to conform with
the charging chart, using the liquid pressure and temperature to
read the chart.
Table 18 — Using Plotted Operating Point
FINAL CHECKS
Ensure that all safety controls are operating, control panel covers
are on, and the service panels are in place.
1. Copeland is a trademark of Emerson Climate Technologies.
0
10
20
30
40
50
60
70
80
90
100
110
120
0
10
20
30
40
60
70
80
90
50
Compressor Unloaded Run Time (Minutes)*
*Times are approximate.
NOTE: Various factors, including high humidity, high ambient
temperature, and the presence of a sound blanket will
increase cool-down times.
Recommended Cooling
T
ime*
(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