Air Dryers—A-4400 Series Technical Bulletin
17
3. Turn the expansion valve adjusting screw to provide an evaporator
pressure that corresponds to the ambient temperature determined in
Figure 5. Turning the screw clockwise increases the pressure;
counterclockwise decreases the pressure. One complete revolution
(360 degrees) equals a pressure change of approximately 10.5 psi
(73.5 kPa).
Note: If when adjusting the screw clockwise and counterclockwise,
the expansion valve does not respond and the evaporator
pressure remains high, a foreign object may be lodged in the
expansion valve orifice. To clear the orifice, turn the
expansion valve adjusting screw clockwise as far as possible,
taking note of the number of revolutions made. Then return
the screw counterclockwise to its original position and check
the evaporator pressure.
4. Allow 20 minutes running time to stabilize the system, then reset the
refrigerant pressure if required.
If after adjusting the expansion valve setting, the evaporator pressure is
still too low, the refrigerant charge is probably low. To recharge the
system, proceed as follows:
1. Disconnect the power supply to the air dryer.
2. Remove the filter bowl and test for possible internal refrigerant leaks
by allowing a small amount of supply air to pass through the unit.
Check for traces of gaseous refrigerant in the escaping air using a
HFC-134a detector at the condensate drain trap (refer to Figures 10
and 11). If an internal leak is discovered, unit replacement is
required. Reinstall the filter bowl when testing has been completed.
3. Using a HFC-134a detector, test for possible external refrigerant
leaks, paying particular attention to all solder joints. If an external
leak is discovered, proceed as follows:
Note: The service valve (as illustrated in Figures 8 and 9) provides
access to the evaporator for checking or servicing. The
service valve is a Schrader type valve with a sealing cap.
To use the valve, unscrew the cap to expose the Schrader
valve pin.
a.
Use a vacuum pump to evacuate the unit of all refrigerant into an
approved refrigerant receptacle before repairing leaks.
b.
Repair any external leaks found using hard solder and flux.
