Oil return to the compressor by means of suction line critical problems in the cooling system.
Returning oil is a mixture of oil and refrigerant.
The mixture thickens as the temperature drops.
Mixture travels, mainly along the inner wall of the pipe or tube.
Mixture travels in severity and actions (speed) of the refrigerant vapor.
Observe these warnings;
Keep the mixture as smoothly as you can,
Slope down to the horizontal suction line of the compressor.
It is important to leave enough of the refrigerant vapor speed make the mixture along the pipe.
Speed horizontal should be not less than 500 ft./min 750 ft./min If the refrigerant vapor should flow up the suction line, speed in vertical pipes or pipes should be not less than 1000 ft/min 1500 ft/min (He must overcome gravity and viscosity.) Be sure to install a small U traps on the basis of vertically upwards flow suction line. These traps prevent a large gulp of oil returning to the compressor during system startup.
Viscosity of oil, refrigerant determines how easily it flows.
Viscosity is measured using a device called Universal viscometer, and is expressed in the pas (Saybolt Seconds Universal) units. Oils containing dissolved refrigerant has a lower viscosity (threads easier). As oil goes into the suction line is getting warmer (suction superheat). She also loses some of the dissolved refrigerant. Tests have shown that the viscosity of the oil, actually increases as you move through the line suction side of the compressor. The longer the suction line, the more you should be careful to ensure proper suction line speeds and oil traps. In the low-temperature systems, the refrigerant dissolved in oil is the most important factor that will help viscosity low enough to return oil.
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