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Service technicians will often spend countless hours leak checking refrigeration or air conditioning systems and not find the leak. When a refrigeration system has lost most of its refrigerant charge in a short period of time, the leak is probably significant and should be easy to find.
Locating the Leak
Today’s sensitive electronic leak-detection systems can pick up a leak of less than one ounce per year. Even bubble solutions are getting so chemically sophisticated that even the smallest leaks will show up as small white “cocoons” of bubbles or foam.
If the system has lost all of its refrigerant charge, a trace gas of refrigerant backed by pressurized dry nitrogen can help the service technician find the leak with the added nitrogen pressure. The trace gas of system refrigerant is simply used to help electronic leak detectors discover the leak. Safety precaution: Never pressurize the system any higher than the system’s nameplate low-side test pressure to prevent tubing rupture. The trace gas should be the same refrigerant that is employed in the system. After leak checking, the mixture of nitrogen and refrigerant trace gas can be vented to the atmosphere.
Many technicians will simply top off a leaky refrigeration system with refrigerant if a leak cannot be found. If a system contains less than 5 pounds of refrigerant, topping off is legal. However, an environmentally conscious service technician should spend the extra time to find the leak, recover and/or pump down the system, fix the leaky troubled spot, evacuate the system to 500 microns, and recharge the system.
Many times, service technicians will encounter water-cooled condensers in their service ventures. Let’s consider a tube-within-a-tube or double-tube water-cooled condenser (Figure 1). These condensers are also often referred to as coaxial condensers. They are often used indoors and are controlled by a water regulating valve which receives a pressure signal from the high side of the system. The water-regulating valve delivers water first to a water jacket wrapped around the compressor’s motor barrel. This happens because the compressor is an air-cooled compressor, but has no condenser fan to deliver air across it because the system is water cooled. Water from the water jacket now travels through the double-tube condenser, which is nothing but a copper water tube inside a steel shell with refrigerant desuperheating, condensing, and subcooling inside the outer shell. However, if the inside copper water tube develops a leak, higher-pressure refrigerant will leak inside the water system and will end up flowing down the water drain pipe as a vapor.
A service technician can use an electronic leak detector in the water drain area for the water-cooled condenser (Figures 2 and 3). When the refrigeration system tonnage is small enough, many municipalities will allow for the water to simply flow down a drain instead of having a cooling-tower loop to conserve water.
In the instance referenced, of the technician using the detector in the water drain area, he actually spent three hours leak checking the entire system before thinking to move to the next room where the water drain was located. The leak was finally found simply by placing the electronic detector near the water drain area for the water-cooled condenser. The technician never thought that the double-tube condenser may be the suspect because of its rugged construction. The double-tube condenser will have to be replaced because of the leaking inside tube. These leaks often go overlooked and service technicians give up trying to find the leak. The end result usually ends up with the technician topping off the system, which is a very environmentally unfriendly remedy with systems with less than 5 pounds of refrigerant.
Why is it Leaking?
Technicians may often recover refrigerant from a system having a water-cooled condenser. During the recovery process, much of the liquid refrigerant will vaporize, creating an evaporator or cooling effect inside the refrigeration tubing. If this evaporator effect is severe enough, the water inside the copper inner tube of the double-tube evaporator will freeze. As ice forms, expansion takes place and the inner tube may crack and form a small fracture or fissure. The system now has a place for high-pressure refrigerant to enter. The remedy for this is to always keep the water flowing through a water-cooled condenser while recovering refrigerant. This will add enough heat load from the flowage of water to prevent water from freezing inside the inner tube of the double-tube condenser.
If a water regulating valve is experiencing water hammer from being either oversized or undersized, the shock from the water hammer may often rupture water tubes in condensers, causing the same problems.
Publication date: 6/3/2013