Pneumatech AD Series, Owner'S Manual

COMPRESSOR 

HOT GAS BYPASS VALVE 

Refrigerant compressors normally do not need any 
maintenance. The compressor will unload or adjust for 
different load conditions with the refrigeration controls. 
Any time power is applied to the compressor, and the 
suction pressure is higher than the specified readings, 
the compressor is either not pumping or failed 
electrically, or tripped “off” at the overload protection. If 
the compressor does not automatically reset within a few 
minutes, it requires servicing. Service must be 
performed by a qualified refrigeration technician. 

These air dryers come equipped with modulating hot gas 
bypass valves. This valve maintains the refrigerant 
suction pressure in varying load conditions. The dryer 
will run from no load to full load conditions without 
freeze-up. The operation of this valve is automatic. If the 
valve needs adjustment, turn the adjusting stem 
clockwise to raise the suction pressure, and 
counterclockwise to lower the suction pressure. This 
adjustment should be made under a no-load condition 
only. When the adjustment is made, turn one quarter of 
a turn at a time, and wait 3 to 5 minutes between 
adjustments. Once the adjustment is complete, secure 
the adjusting stem with the locknut that is provided. 
Careful adjustment of this valve is necessary for normal 
operation of the air dryer. Hot gas bypass valve 
adjustment may be made by maintenance personnel. 
See Figure 5. 

EXPANSION VALVE 

Air dryers equipped with an automatic expansion valve 
are factory adjusted for proper cooling. The valve 
adjusting stem is secured with a lock nut at the factory to 
maintain proper setting. Larger units are equipped with a 
thermostatic expansion valve, factory set to maintain a 
superheat of 8 to 10°F (-13 to -12°C). These valves do 
not need adjustment in normal operation. Generally, 
superheat adjustments are needed only at the time of 
valve replacement. Expansion valve service must be 
performed by a qualified refrigeration technician. 

FIGURE 5 — HOT GAS BYPASS VALVE ADJUSTMENTS 

 
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