Carrier 38AUZ - Manual (Page 15)

15
ADVANCED SCROLL TEMPERATURE PROTECTION
(ASTP) — Advanced Scroll Temperature Protection (ASTP)
is a form of internal discharge temperature protection, used in
38AUZ*12 and 38AUZ*14 units, that unloads the scroll com-
pressor when the internal temperature reaches approximately
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 un-
loaded, the longer it must cool before the bi-metal disk resets.
See Fig. 14.
Fig. 14 — Recommended Minimum Cool-Down Time
After Compressor is Stopped
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 automatically before the motor protector resets, which
may take up to 2 hours. A label located above the terminal box
identifies Copeland Scroll compressor models (ZP103 and
ZP137) that contain this technology. See Fig. 15.
Fig. 15 — Advanced Scroll Temperature
Protection Label
START UNIT — The field disconnect is closed, the indoor
fan circuit breaker is closed, and the space thermostat is set
above ambient so that there is no demand for cooling. Only the
crankcase heater will be energized.
Reset the space thermostat below ambient so that a call for
cooling is ensured.
ADJUST REFRIGERANT CHARGE — The unit must be
charged in Cooling mode only. Refer to Cooling Charging
Charts, Fig. 16 through Fig. 19. For applications with line
lengths greater than 100 ft, contact Carrier representative. 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 sub-
cooling 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 out-
door ambient temperature does not affect the reading. Indoor
airflow must be within the unit’s normal operating range. Oper-
ate the unit for a minimum of 15 minutes. Ensure that pressure
and temperature readings have stabilized. Plot the liquid pres-
sure 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.
0
10
20
30
40
50
60
70
80
90
100
110
120
0 10 20 30 40 50 60 70 80 90
Compressor Unloaded Run Time (Minutes)
R
ec
om
m
ende
d C
ool
ing
Ti
m
e
(Mi
nu
tes
)
*Times are approximate.
NOTE: Various factors, including high humidity, high ambient tem-
perature, and the presence of a sound blanket will increase cool-
down times.
Never charge liquid into the low-pressure side of system.
Do not overcharge. During charging or removal of refriger-
ant, be sure indoor-fan system is operating. Ensure both
outdoor fan motors are running; bypass any Motormaster
function.