Carrier 38AU - Manual (Page 20)

20
Advanced Scroll Temperature Protection (ASTP)
A label located above the terminal box identifies Copeland
Scroll compressor models that contain this technology. See Fig.
17. 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 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 bal-
ance while the motor continues to run. The longer the compres-
sor runs unloaded, the longer it must cool before the bi-metal
disk resets. See Fig. 18.
Fig. 17 — Advanced Scroll Temperature
Protection Label
Fig. 18 — 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.
Start Unit
Set the space thermostat to a set point above space temperature
so that there is no demand for cooling. Close the 38 AU discon-
nect switch. Only the crankcase heater will be energized.
Reset the space thermostat below space temperature so that a
call for cooling is ensured.
Adjust Refrigerant Charge
The unit must be charged in Cooling mode only. Refer to Cool-
ing Charging Charts, Fig. 19 through Fig. 22. 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 tem-
perature 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 tempera-
ture 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
e
c
o
m
m
e
nde
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
or mild-ambient control function.