Common Faults and Troubleshooting Procedures for Refrigerated Compressed Air Dryers

I. Refrigeration System Faults
1. Clogged Expansion Valve
A. Symptoms: No refrigerant flow observed through the sight glass; frost/ice forms at the expansion valve outlet; high-pressure pipe overheats or high-pressure shutdown occurs.
B. Causes: Dirty blockage, ice blockage, breakage of temperature-sensing capillary tube.
C. Troubleshooting Procedures:
Adjust the expansion valve superheat and opening stroke;
Increase superheat of the sensing bulb and raise PS pressure. For example, cover the sensing bulb by hand or immerse it in warm water;
Raise refrigerant high pressure (fan switch setting value), close the hot gas bypass valve to flush out dirty blockage.
2. Clogged Filter Drier
A. Symptoms: Obvious temperature difference between the inlet and outlet of the filter drier, or condensation at the filter outlet.
B. Troubleshooting Procedure: Replace the filter drier.

Note: When the system is blocked, high and low pressure readings may stay within normal range under no-load operation. During loaded operation, 

high pressure rises severely and may trigger high-pressure trip. After long-time running, massive high-temperature and high-pressure gas flows through the hot gas bypass directly into the low-pressure suction line.

 This overheats the compressor; the temperature of the high-pressure suction pipe may exceed 100°C and even burn out the motor.

When the compressor overheats, the built-in thermal protection will activate. The unit can only be restarted after the compressor naturally cools down.
3. Compressor Faults
A. Causes: Overload, burnt motor, long-term abnormal operation of the dryer, refrigerant leakage, damaged starting capacitor (small-size models), etc.
B. Diagnosis Methods:
Judge by measuring motor resistance:
Three-phase motor:
ROA = ROB = ROC
Single-phase motor: ROA = ROB + ROC
(ROB = ROA + ROC)
(ROC = ROA + ROB)
Measure compressor insulation resistance to ground.
Inspect the supporting capacitor of the compressor (equipped on ND-05 ~ ND-100AC dryers).

Capacitor testing method: Set the multimeter to the highest resistance range (above 200 MΩ). Connect two probes to both terminals of the capacitor. For both digital and analog multimeters,

 the resistance reading rises slowly after an initial low value. Larger capacitance leads to slower resistance rise. If the reading remains at 0 or ∞ without variation, the capacitor has electrolyte leakage or breakdown.

Check whether the compressor runs or generates abnormal noise after startup; touch the middle section of the compressor to check overheating. Inspect compressor seizure. If necessary, 

tap the middle part with a rubber mallet or wooden stick, then restart to observe compressor action.

Measure compressor operating current with an ammeter to verify normal operation.
4. Refrigerant Leakage in Refrigeration System

A. Symptoms: After shutdown, high-pressure and low-pressure refrigerant gauges read zero or below 0.4 MPa. During operation, the compressor and high-pressure pipes run hot; 

both refrigerant high and low pressure tend to be low. Severe leakage will trigger low-pressure alarm.

B. Troubleshooting Procedures: Locate leaks, repair leak points, recharge refrigerant and perform readjustment.
C. Diagnosis Method for Internal Evaporator Leakage (close the service valve):
① Stop the dryer and fully recover all refrigerant from the refrigeration system until pressure gauges show zero.

② Open the compressed air inlet valve to let compressed air pass through the evaporator. Observe readings of the refrigerant pressure gauge. If the evaporator has internal leakage, 

the gauge pressure will gradually rise and approach compressed air working pressure, confirming internal evaporator leakage.

D. If the refrigerant gauge shows no obvious change or only slight pressure rise after introducing compressed air, internal evaporator leakage cannot be confirmed. 

A small amount of refrigerant dissolves in refrigeration oil and releases slowly over time.

II. Air System Faults
1. Pressure Drop between Equipment Air Inlet and Outlet
Troubleshooting Procedures:
A. Ice blockage inside evaporator with low refrigerant low pressure; adjust refrigerant low pressure above 0.35 MPa;
B. Failed pre-filter element on compressed air inlet;
C. Defective air pressure gauge;
D. Severe air leakage from drainage system.
2. Insufficient Moisture Removal of Air System
Troubleshooting Procedures:
A. Seriously low compressed air inlet pressure;
B. Drainage system fails to discharge water; short timing setting of electronic drainer;
C. Float drainer clogged with dirt; untimely manual blowdown;
D. Replace filter element.
III. Electrical System Faults
1. Open Circuit of High/Low Pressure Switch
Troubleshooting Procedure: This is a protection action. Manually reset and inspect the refrigeration system.
2. Open Circuit of Thermal Overload Relay
Troubleshooting Procedures:
Check the current rating of the thermal relay and measure actual operating current.
3. Unit Fails to Start After Pressing Start Button
Troubleshooting Procedures:
Poor electrical contact;
Tripping of high/low pressure switch or temperature switch protection;
Delay countdown not completed;
Inspect the control system circuit.
4. Air Circuit Breaker Trips Upon Startup
Troubleshooting Procedures:
A. Check circuit for short circuit or open phase caused by poor contact;
B. Inspect AC contactor;
C. Measure actual operating current;
D. Test compressor motor resistance to judge compressor condition.
5. Blown Fuse in Control System
Troubleshooting Procedures:
A. Check coil resistance of electronic drainer for short circuit;
B. Locate short-circuit position according to control system schematic diagram.
6. Compressor Does Not Run After Power-on
Troubleshooting Procedures:
Check power phase sequence and refer to electrical schematic;
Power supply cable fails to meet specification;
Compressor malfunction.
IV. Drainage System Faults
Ice blockage at drain outlet: Adjust refrigerant low pressure to normal value.
Float drainer clogged: Clean the float drainer.
Electronic drainer fails to drain: Inspect the coil of electronic drainer and refer to electrical schematic.
Importance of Drainage System

If condensed water separated by the dryer cannot be drained promptly, airflow will carry condensate out of the dryer to downstream air consumption points, 

resulting in moisture contained in compressed air. Operators shall frequently use the manual drain button ESC for blowdown, 

observe the draining cycle of the electronic drainer and reset timing parameters as required.