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Refrigeration Capillary Tube Troubleshooting for Technicians

A capillary tube is found in wide variety of refrigerators, water coolers, air conditioners and deep freezers. This component connects the condenser to the evaporator, and its length determines the airflow at a specific pressure. Sometimes, issues can pop up that prevent cooling and from happening. the capillary tube can be blocked by solid residues affecting the performance of the refrigerator. In this guide, we help technicians in HVAC/R with refrigeration capillary tube troubleshooting to diagnose and remedy the problem fast.

What is the Purpose of a Capillary Tube?

The capillary tube is the essential control device used in air conditioning and refrigeration systems (HVACs). Most capillary tubes are of extended length but are coiled several times, so they take less space. It allows the coolant to pass through the tube at decreasing pressure and increasing speed, resulting in evaporation at the end of the tube. Evaporation occurs at the temperature of 32°F (0°C) in the negative range, causing thermal exchange that eventually cools the unit.

It's essential to take extra care during the tube placement to avoid any blocking and obstructions. Solid dust particles, moisture and tube bending can result in partial or complete blockage of airflow and prevent cooling.

Refrigeration Capillary Tube Troubleshooting

Below are four common problems that can pop up in capillary tube and how to solve them:

1. Clogged Capillary Tube

  • Potential cause: If the capillary is blocked, the airflow stops feeding the evaporator, causing a drastic drop in pressure leading to a high workload on the compressor. This ultimately increases the overall system temperature.
  • Remedy: To prevent clogging, it is necessary to use a dry filter with metal mesh to avoid entering impurities into the capillary tube.

2. Dirt or Debris Blocking

  • Potential cause: Some dirt and small particles can pass through the mesh screen and create a buildup and blockage. Usually, the system keeps working instead of blocking and low pressure until the tube is completely blocked.
  • Remedy: To resolve this issue, use a heavy-duty pipe cleaner or screwdriver and place it vertically on the tube cap. Gently tap on handle or top. This will help unclog debris. If the blockage didn't unclog, change the filter mesh of the cap tube.

3. Moisture Freezing Within a Tube

  • Potential cause: An unacceptable level of moisture can also cause malfunctioning, which often occurs due to poor location.
  • Remedy 1: If moisture turns to ice, it can be removed by putting a hot wet towel at one end of the cap tube of the evaporator. This melts the ice and helps remove the blockage.
  • Remedy 2: Wax builds up in the tubes from a combination of dirt, debris and moisture. If this happens, dry the filter to remove the formation of wax.

4. Oil in The Capillary Tube (Hydraulic Lock)

  • Potential cause: Sometimes, refrigerant oils keep circulating in the coil and are pushed back into the capillary tube at the end of the evaporator, blocking the system. This is known as hydraulic lock and can occur over time.
  • Remedy: Apply heat to the cap tube at the coil entrance, lowering the oil's thickness and helping it clear the capillary tube. Heat can be applied using a hot, wet towel several times.
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