The first thing you must establish in changing a compressor was the nature of the failure. Of course if it was a mechanical problem such as a broken connecting rod, the changing of the compressor is relatively simple. In the case of an electrical failure, the clean-up is rather specific. Many times a service company can’t seem to keep a compressor operational in a certain installation. The reason is the improper procedure was followed.
The severity of the burn-out is apparent sometimes when the refrigerant lines are bled. The stench of burned refrigeration oil is unmistakably pungent. Exercise extreme caution in regard to the exhausting vapor; keep if from your skin and eyes. In Chapter 14 you were told about the acid formation in refrigeration systems. Always assume the oil has acidity, and you won’t get into any trouble.
When the system pressure is equalized with the atmosphere, begin taking the compressor loose from its mountings and piping. Assume nothing, spill some oil from the old compressor into a clean jar. Perform an acid test with the acid kit. The directions come in each kit. Even when there is not a foul smell to the refrigeration oil, acid still could be present in the system. If this is not done and acid is present, the insulation on the new compressor’s winding will be attacked and destroyed causing electrical failure. The time between the installation and the failure is governed by the concentration of acid in the oil.
The number one thing to do is rid the system of the acid. On most commercial units using a semi-hermetic compressor changmg oil is comparatively easy. There are two schools of thought about acid clean-up in a system. One is to change the suction line filter driers often, and the other is change the oil often. I’ve found that changing the oil and the filters is the only way to do a thorough job. Oil acts like a sponge soaking up moisture and acid. It might take several oil changes with several hours of compressor running before all traces of acid are removed.
In some commercial units, when the evaporator coil is lower than the condensing unit, it helps to place a drain valve in the lowest point of the coil. This valve is used to release any oil that might be trapped in the evaporator. With the new compressor in operation,
the oil level milflt be AeM and IWHlflht tfl tllfi WW M TlUS is done on most semi-hermetic compressors with the crankcase sight glass.
When working on a hermetic compressor installed in a residence, the clean-up procedure is somewhat different. All manufacturers of compressors place an oil charge in the compressor when it is shipped from the factory. The compressor you are to change also has a factory oil charge in it. Oil amounts measured in ounces is not very much, yet a few more ounces than needed can create problems in a compressor. For this reason, care must be taken to measure the amount of oil reclaimed during the compressor change out.
I carried a kitchen measuring cup with a 32-ounce capacity. When the compressor was removed from the cabinet of the unit, I would pour the oil from the compressor into the measuring cup. If a compressor had a 14-ounce capacity, and only eight ounces were in the cup, six ounces were still in the system. With the use of nitrogen enough pressure can be placed into and through the piping to remove the sue ounces. R-12 refrigerant can also be used as a flushing agent to remove contaminated oil from the system.
After all of that, install a suction line drier filter. In most cases, residential units were not equipped with them. Some have liquid line driers. If the unit you are working on has a liquid line drier on it, change it and then install a suction line drier. I also recommend the use of flare fittings on the suction drier, if possible. The suction line drier should be changed after running in the unit for a few days. There should be about 40 hours running time on the filter. Of course this is only an average. Clean-up of a real bad bum requires that the filter drier be changed after several hours of initial start-up of the new compressor.
It is difficult to get an oil sample from a small hermetic residential unit. For this reason, make your clean-up a proper one. Oil can be felt in the hot gas of the discharge line. This oil should only present itself in a vaporized mist. If it is experienced as oil droplets, the system has an overcharge of oil in it. This is a situation that can cause problems with the compressor, depending upon the amount of the excessive oil. The only way to remove some of it is by letting it escape from the discharge line. Of course this method requires you to top off the charge before you leave the unit.
Acid test kits are a valuable tool and not used enough by many technicians. In many commercial preventive maintenance programs that you implement, it should become standard procedure to take an acid test of a unit once a year. In many cases, a compressor could be saved by an oil change. When acid starts to form, but is removed before attacking the motor windings of the compressor, it does no harm. Years ago, an acid sight glass was used on large commercial units. This sight glass had a fine piece of copper placed where the moisture indicator is. When the service technician checked the refrigerant level in the sight glass, he was also able to see if any deterioration was taking place with the fine copper wire. If so, it alerted him to start a neutralization program. He immediately instituted oil changing keeping a constant eye on the acid sight glass to see if it progressed or ceased. I’ve not seen this type sight glass in parts houses for a long time. Stopping things before they happen is a big part of your job. A few drops of grease or oil in a motor bearing stops a growl, and prolongs the life of the motor.