Allied Air Enterprises 4AC16LT - Manual (Page 13)

506467-01 Issue 1008 Page 13
2. Close manifold gauge set valves. Connect the center
manifold hose to an upright cylinder of R410A.
3. If room temperature is below 70°F, set the room thermo-
stat to call for heat. This will create the necessary load
for properly charging the system in the cooling cycle.
4. Use a digital thermometer to record the outdoor
ambient temperature.
5. When the heating demand has been satisfied, switch
the thermostat to cooling mode with a set point of
68°F. When pressures have stabilized, use a digital
thermometer to record the liquid and suction line
temperatures.
6. The outdoor temperature will determine which charg-
ing method to use. Proceed with the appropriate
charging method.
Charge Using Weigh-In Method
If the system is void of refrigerant, or if the outdoor ambient
temperature is cool, first locate and repair any leaks then
use the weigh-in method to charge the unit.
1. Recover the refrigerant from the unit.
2. Conduct a leak check, then evacuate as previously
outlined.
3. Weigh in the charge according to the total amount
shown on the unit nameplate.
If weighing facilities are not available, use one of the
following procedures to charge the unit.
Charge Using Subcooling Method –
Outdoor Temperatures Below 65°F
When the outdoor ambient temperature is below 65°F, the
subcooling method can be used to charge the unit. It may
be necessary to restrict the air flow through the outdoor
coil to achieve pressures in the 200-250 psig range.
These higher pressures are necessary for checking the
charge. Block equal sections of air intake panels and
move obstructions sideways until the liquid pressure is in
the 200-250 psig range (see Figure 12).
1. With the manifold gauge hose on the liquid service
port and the unit operating stably, use a digital ther-
mometer to record the liquid line temperature.
2. At the same time, record the liquid line pressure reading.
3. Use the temperature/pressure chart (Table 5 on page 14)
to determine the saturation temperature for the liquid line
pressure reading.
4. Subtract the liquid line temperature from the satura-
tion temperature (according to the chart) to determine
subcooling.
_____ ° Saturation Temperature °F
_____ ° Liquid Line Temperature °F
_____ ° Subcooling Value °F
–
=
5. Compare the subcooling value with those shown in
Table 6 on page 14. If subcooling is greater than
shown, recover some refrigerant. If subcooling is less
than shown, add some refrigerant.
Charge Using Approach Method –
Outdoor Temperatures 65°F or Above
The following procedure is intended as a general guide
and is for use on expansion valve systems only. For best
results, indoor temperature should 70°F to 80°F. Monitor
system pressures while charging.
1. Record outdoor ambient temperature using a digital
thermometer.
2. Attach high pressure gauge set and operate unit for
several minutes to allow system pressures to stabilize.
3. Compare stabilized pressures with those provided in
Table 8 on page 15. Minor variations in these pres-
sures may be expected due to differences in installa-
tions. Significant differences could mean that the
system is not properly charged or that a problem
exists with some component in the system.
Pressures higher than those listed indicate that the
system is overcharged. Pressures lower than those
listed indicate that the system is undercharged. Verify
adjusted charge using the approach method.
4. Use the same digital thermometer to check liquid line
temperature.
5. Subtract the outdoor ambient temperature from the
liquid line temperature to determine the approach
temperature.
Figure 12
Outdoor coil should be
blocked one side at a time
with cardboard or plastic
sheet until proper testing
pressures are reached.
Blocking Outdoor Coil
Cardboard or Plastic Sheet