Capillary Tubes in 15 Minutes

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Sometimes you do not have the capillary tubes size recommended by the manufacturer. The following J/B conversion chart shows how much longer or shorter the replacement cap tube must be.

• Assume 9 feet of .040 cap tube is needed.
• How long would a .036 tube need to be to give the same amount of refrigerant and pressure drop?
• What if all you had was a .042 cap tube?

For a cap tube to work properly:

• It must be sized properly.
• The evaporator load must be at designed conditions.
• The refrigerant charge must be correct.
• There must be a full column of liquid to the cap tube.

Causes of evaporator flooding in a cap tube system:

• Too much high side pressure
  • Dirty condenser
  • Refrigerant overcharge
• Low evaporator load
  • Box temperature too low
  • Blocked evaporator (dirt or ice)
  • Fan motor bad
• Incorrectly sized cap tube (low pressure drop)
• Inside diameter (I.D.) too large
• Cap tube length too short

Causes of evaporator starving in a cap tube system:

• High side pressure too low.
  • Low on refrigerant.
  • Low ambient.
• High evaporator load (quickly vaporizing refrigerant)
  • Door open or not sealing
  • High product load
    • Initial start-up
    • Hot product in the box
• Incorrectly sized cap tube (high-pressure drop).
• Inside diameter (I.D.) too small
• Cap tube length too long.

Cause for plugged cap tubes:

• Dirt or ice blocking the cap tube
• Filter desiccant can also plug cap tube

Solution:

• Cut off some cap tube/capillary tubes
• Replace filter drier