Troubleshooting Methods for Refrigerant Leakage of Refrigerated Compressed Air Dryers

The most obvious symptom of refrigerant leakage in a refrigerated air dryer is a zero reading on the refrigerant pressure gauge. 

To tackle refrigerant leakage, the first priority is to locate the leak point, which requires patience, careful inspection and proper methods.

The inspection procedure is as follows: Start with visual inspection. Open the machine cabinet panel and check the interior. 

Since compressor lubricating oil mixes with refrigerant during operation, refrigerant leakage will carry lubricating oil out. Carefully examine the inside of the unit; patchy oil stains are highly likely to mark leak positions.

Next, inspect thin capillary copper tubes inside the machine, namely copper tubes below 6 mm and process tubes, to check for fractures. 

Mark all suspicious areas after the above preliminary inspection. Then charge inert gas at a certain pressure to confirm leaks. Nitrogen is the preferred medium for pressure holding if available. 

Gaseous refrigerant can be used as an alternative when nitrogen is unavailable. Never use oxygen for pressure testing and leak detection, as this poses a fatal safety hazard.

What is gaseous refrigerant? Place the refrigerant cylinder upright; gaseous refrigerant discharges from the top shut-off valve. Conversely, 

turn the cylinder upside down with the valve pointing downward to release liquid refrigerant.

During pressure holding, introduce gas slowly. Observe readings on the dryer’s refrigerant pressure gauge while pressurizing. 

Small-capacity models are only fitted with a low-pressure refrigerant gauge, while units of 15 m³/min and above are equipped with both high-pressure and low-pressure gauges. 

Pause pressurization at approximately 0.2 MPa (2.0 kgf). Listen carefully for any hissing leakage sound inside the machine; the leak can be located according to the sound source if detected. 

If no leakage noise is heard, continue pressurizing to 0.4–0.5 MPa. Dip a sponge in soapy water, test the previously marked suspicious positions first, then check all internal pipe connections (copper nuts).

Bubbles will emerge at leak points, so thorough inspection is essential.

If no leak is found via the above steps, internal leakage inside the evaporator is suspected, which is rather complicated to repair. Confirmation is required first: 

disconnect the evaporator from the refrigeration system and perform independent pressure testing. A pressure drop during isolated pressure holding confirms evaporator internal leakage.

Another relatively simple verification method: open the compressed air inlet. If the refrigerant gauge pressure rises after some time, 

it proves the refrigeration system communicates with the air system. The evaporator is the only heat exchange component between the two circuits, confirming internal evaporator leakage.

After locating leaks, carry out repair work accordingly. For loose flare connections, simply tighten with a spanner. For leaks on welded copper tubing, 

brazing is required. Brazing is one of the most common techniques in refrigeration maintenance. It uses an oxy-acetylene flame to heat low-silver brazing filler metal and the joint to be repaired, 

melting the filler metal and base metal together to seal the leak.

Before brazing, fully release pressure from the refrigeration system to zero. Operate the brazing torch: open acetylene first, ignite the flame, 

then gradually feed oxygen, adjusting the oxygen-acetylene ratio to form a neutral to slightly oxidizing flame. Heat the joint and silver brazing rod until fusion occurs. 

Operators need professional training to master proper techniques. After leak repair, perform system pressure holding again to verify welding quality.

Once leak sealing is completed, evacuate the system, then charge liquid refrigerant of specified mass (refer to basic configuration sheet for exact volume). 

Refrigerant shall be charged through the dedicated liquid charging Schrader valve on the dryer. For large-size units, start charging refrigerant from the high-pressure charging port. 

If the full specified charge cannot be completed in one go, start the unit and slowly top up refrigerant from the low-pressure side until reaching the required dosage.