HVACR field service terminology is often confusing and misused even by the most seasoned service veterans. Two important service terms that are often misunderstood and misused are ‘flooding’ and ‘slugging.’ Each one will be thoroughly defined and explained as they apply to refrigeration and air conditioning compressors.
Systematic troubleshooting using a system check sheet is still the best method for the conscientious service technician to pinpoint hard-to-find system problems. Here we will explore how evaporators can become oil logged, and include symptoms with explanations for a system with an oil-logged evaporator.
Refrigerant migration is defined as refrigerant, either liquid or vapor, traveling to the compressor’s suction line or crankcase during the off cycle. During the off cycle, or especially during a long shutdown, refrigerant will want to travel, or migrate, to a place where the pressure is the lowest.
Many service technicians believe that if there is frost on the compressor’s head, there is cause for alarm. This is simply not true. Frost is simply frozen dew. Consider a low temperature commercial refrigeration application operating with 7° of evaporator superheat and 40° of compressor superheat.
My column in the March 8 issue of The NEWS dealt mainly with reciprocating compressors experiencing low head pressure and high suction pressure from bad valves. This column takes an in-depth look at high compression ratios that cause compressor overheating along with high compressor discharge temperatures.
Many servicemen experience service calls where the compressor has both a low head pressure and a high suction pressure. There are three main reasons why a reciprocating compressor will simultaneously have a low head pressure and a high suction pressure.
Oil safety controllers often come in two types: bellows (mechanical) and transducer (electronic). Bellows-type controllers sense crankcase pressure and oil pump discharge pressure, usually through some type of tubing, and then transmit the pressure to flexible bellows. Transducer-type controllers use a pressure transducer.
Many larger compressors in the refrigeration and air conditioning field have forced-oiling systems. These compressors are usually over 5 hp. They contain an oil pump located at the end of the compressor’s crankshaft. The crankshaft is actually connected to the oil pump and supplies power, which turns the oil pump.
The problem we are going to deal with here pertains to a restricted liquid line after the receiver. Provided is a service checklist. Assume that the refrigeration system is a TXV/receiver system, employing a filter drier and sight-glass. The system has R-134a as the working refrigerant.