The size of the capillary for a 1/4 HP compressor primarily depends on the type of refrigerant gas used and the temperature of the evaporator in the application
The best way to select a capillary is not to use the HP of the compressor motor as a reference. Instead, it is advisable to consider the cooling capacity of the compressor, which is typically measured in Btu/h and Kcal/h.
However, there are cases where the cooling power data for compressors may not be available, and in such situations, we still need to determine the size of the capillary tube.
The issue with using 1/4 HP as a reference is that it is an electrical parameter, which introduces the motor’s efficiency factor into the equation, while disregarding the efficiency of the compressor itself.
For the selection of the capillaries the following reference is taken into account:
Condensing temperature _ | ||
| LBP Low Pressure | -23,3 °C -10°F | 54,4 °C 130°F |
| MBP Medium Pressure | -6,7 °C 20°F | 54,4 °C 130°F |
| HBP High Pressure | 7,2 °C 45°F | 54,4 °C 130°F |
Capillary measure for 1/4 compressor Rules:
- Capillary tubes depend on both their length and diameter to determine their overall restriction.
- A percentage change in diameter can affect the flow more significantly than an equivalent change in length.
- The restriction can also be adjusted by either lengthening or shortening the tube.
- As a general rule, the longer the tube, the slower the flow. However, there comes a point where excessively increasing the tube’s length to enhance restriction and reduce flow becomes inefficient and often futile.
- Conversely, as the tube’s length decreases, the flow gradually increases until it reaches a critical point, where the flow rate starts to increase more rapidly with each further reduction in length.
- If the length is further reduced, it reaches a stage where even minor alterations in length result in significant increases in flow.
- At this point, the tube behaves less like a capillary tube and more like an orifice.
- As a practical recommendation, it’s advisable to keep the tube length within a range of no less than 5 feet and no more than 16 feet.
- While exceptions may exist, adhering to this guideline for daily operations will help minimize many potential issues.”
What capillary does a 1/4 HP compressor have with R134a?
| diameter in | length m | |
| HBP | 0.042 | 1.8 |
| MBP | 0.042 | 2.0 |
Capillary for 1/4 HP motor with R-410A?
| T= -10°F -23.3°C Diameter/ length | T= 25°F -3.89°C Diameter/ length | T= 45°F 7.2°C Diameter/ length |
| 0.031 in 73″ | 0.031 in 40″ | 0.042 in 101″ |
What capillary does a 1/4 compressor use for R404A?
| Power | Condition | Diameter and Length |
| 1/4 HP | Evaporation temperature =-23°C ONLY When the compressor reaches a cooling capacity of 1000 Btu/h | 0.031″ – 4½ ft |
| 1/4 HP | Evaporation temperature =-6.7°C ONLY When the compressor reaches a cooling capacity of 1000 3000 Btu/h | 0.052″ – 8½ ft |
Table of capillary tube compressor 1/4 HP for R22
| HP | diameter in | length m | |
| 1/4 | HBP | 0.050 | 3.0 |
| 1/4 | MBP | 0.036 | 2.5 |
Table of Capillary Tube R407C Compressor 1/4HP:
| Low Temperature Diameter in Length in | Average Temperature Diameter in Length in | High Temperature Diameter in Length in |
| 0.031 56″ | 0.031 31″ | 0.042 79″ |