Allied Air Enterprises 4AC18LT - Manual (Page 14)

506469-01 Issue 1008
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 be 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 pressures may be
expected due to differences in installations. 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 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.
=
_
Liquid Line Tempera
Saturation Tempera
Subcooling Value °F
°
°
Page 14 of 24
1. Connect the manifold gauge set to the service valve ports
as follows (See Figure 13):
• Low pressure gauge to suction line service valve
• High pressure gauge to liquid line service valve
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
thermostat 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 charging
method to use. Proceed with the appropriate charging
method.
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 11).
1. With the manifold gauge hose on the liquid service port
and the unit operating stably, use a digital thermometer 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 saturation
temperature (according to the chart) to determine subcooling
CARDBOARD OR
PLASTIC SHEET
Blocking Outdoor Coil
Figure 11
Outdoor coil should be
blocked one side at a time
with cardboard or plastic
sheet until proper testing
pressures are reached