10
Air Dryers—A-4400 Series Technical Bulletin
The evaporator pressure gauge is calibrated to a test gauge at the factory.
Readings are recorded on a label inside the dryer cabinet base. Apply this
correction to the evaporator gauge to obtain a precise reading.
The A-4400 Series Refrigerated Air Dryers are factory set to protect
against air side freeze-up down to ambient temperatures of 40
°
F (4
°
C) and
altitudes up to 1500 ft.
Using the corrected no load evaporator pressure gauge reading and current
ambient temperature, refer to the graph in Figure 5 to determine if the
evaporator pressure is at the proper setting. If the value is within the
acceptable operating zone as shown on the graph, then no further
adjustments are necessary. If the value is not within the acceptable
operating zone, then it will be necessary to adjust the expansion valve.
Refer to the Refrigeration Service section and follow Steps 1 through 5
(readjusting the expansion valve setting) to properly adjust the expansion
valve until the evaporator pressure gauge is at the adjusted pressure.
Note: All of the expansion valve settings are based on no load
conditions, position the service bypass valve into the bypass mode.
Allow the unit to run unloaded a minimum of 10 minutes prior to
checking evaporator pressure or adjusting the expansion valve.
If the air dryer is installed in high altitudes, the expansion valve will
have to be adjusted to compensate for the new ambient pressure.
For altitudes from 1500 to 5000 ft, increase the expansion valve setting by
2.5 psig (17.5 kPa), and for altitudes over 5000 ft, increase the expansion
valve setting by 4.0 psig (28 kPa). This increase in evaporator pressure
must be added to the value determined by the graph in Figure 5 to account
for altitude effects. Refer to the Refrigeration Service section and follow
Steps 1 through 5 (readjusting the expansion valve setting) to properly
adjust the expansion valve until the evaporator pressure gauge is at the
adjusted pressure.
Example:
If:
Altitude = 4000 ft above sea level
Ambient temperature = 80
°
F
Evaporator pressure gauge reading at no load condition = 34.8 psig
Then: Corrected evaporator pressure = 34.8 psig + 2.5 psig = 37.3 psig
Gauge
Correction
Pressure
Adjustment
Compensation
