When lower-than-normal pressures are observed on both the high and low sides and the system does not cool properly, look for a refrigerant leak. This is done with a leak detector (see fig. 82a). Pass the probe of the detector over the suspected joints in the system. As the leak is approached, the detector gives off a piercing sound. Some leak detectors also come with a light that flashes. Some are sensitive enough to detect a leak of as little as 0.05 ounce per year.
Before getting into the repair procedures, note that there are systems of either copper or aluminum. Should you receive a call from a home owner stating that he/she has poked a hole in the evaporator in an attempt to more quickly defrost it, it may be concluded that it is a manual- or cycle-defrost refrigerator and that the evaporator is probably made of aluminum. Advise the owner to immediately unplug the unit to prevent any further damage to the compressor due to moisture penetrating the system. If the unit continues to run, the compressor will be ruined in no time.
Any repair of an aluminum evaporator is made with an epoxy instead of brazing. The high temperatures produced by brazing cannot be used on aluminum that has a low melting point.
Aluminum repair kits are available at regular supply houses. They contain a tube of resin, a tube of hardener, a vial of cleaner (acetone), emery cloth, mixing spatulas (popsicle sticks), and a piece of aluminum foil patching. These kits contain easy-to-follow instructions; but most important of all is the absolute thorough cleaning of the surface prior to applying the epoxy. It cannot be stressed too much how important it is to use the acetone to thoroughly clean the area to be repaired. Any trace of dirt, oil, or residue does not allow the repair substance to adhere.
Any time the sealed system is opened, the filter-drier must be replaced with a new one.
When a large leak is found in copper tubing, it is sometimes easier to cut the tubing and reconnect it by flaring or silver brazing. Prior to silver brazing, use a short length of copper tubing with an inside diameter equal to the outside diameter of the tube being repaired to join the two ends. This makes an excellent silver-brazed joint. Square off the ends to be joined and clean them thoroughly. Clean the inside of the piece of tubing being used
as a connector, flux the joint areas, center the short piece of tubing over the joint, and braze it.
During the preparation for charging a unit, a few drops of a liquid chemical leak detector can be placed in the inlet hose before connecting it to the compound gauge manifold. (Follow the manufacturer’s instructions on the package.) When the system is charged and resumes running, in case of a leak, the substance appears as a red ring around the hole as it escapes with the refrigerant, making the leak easy to find.