The Case of Flooded Start
Sure, the compressor failed. But in The Case of the Flooded Start, the real culprit was a system failure. Unfortunately, that doesn't let the compressor completely off the hook. System problems like flooded starts can lead to compressor and other damage. What follows is a line-up of the causes and effects of flooded starts on both reciprocating and scroll compressors, and how you can identify and resolve the case.
| Section 1: Identifying the Problem |
| Flooded starts result from migration and can lead to liquid slugging. As the compressor sits idle between cycles, refrigerant vapor travels through the suction line from the evaporator to the compressor. Once in the compressor, the vapor will condense and settle under the oil in the crankcase. This refrigerant migration will continue until the compressor is started for the next cooling cycle. Just as the compressor starts, the liquid refrigerant in the crankcase will explode up out of the oil and will wash away oil from the compressor components in the crankcase. |
| Section 2: The Effects of Flooded Starts On Reciprocating Compressors |
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Flooded starts in a reciprocating compressor can end up damaging various parts in the compressor. Among the parts most often damaged are the crankshaft journals, bearings, and the rods. This crankshaft taken from a refrigerant cooled semi-hermetic reciprocating compressor shows the damage caused by flooded start as the result of migration. |
 As you can see, the shaft shows significant scoring and wear due to the liquid  refrigerant migration. In extreme cases, some liquid refrigerant can get into the cylinders of the compressor. The liquid in the compressor can cause slugging damage, which can do serious damage to the valve plate, discharge reeds, and cantilever backers. In this example, the discharge reeds have all been broken, and the cantilever backer tip has been bent upwards from the liquid slug. |
 This is the side view of the same valve plate. As you can see, the cantilever backer tips have been bent upwards from the liquid slug, making the tips appear higher than the rest of the plate. |
| Section 3: The Effects of Flooded Starts On Scroll Compressors |
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Flooded starts can also adversely affect scroll compressors, causing slugging damage that can possibly break the fixed and orbiting scrolls. As you can see, the liquid slug in this compressor broke off parts of the scroll vanes, destroying the compressor. The probability of liquid migration increases with longer off cycles, faulty crankcase heaters, and wider temperature differentials between evaporator and compressor. |
| This shows another scroll set that was exposed to liquid migration before the compressor was started again. The liquid failed to evaporate, and caused a liquid slug, breaking off almost all of the scroll vanes. To minimize migration, and thus the possibility of a flooded start and the subsequent slugging damage, there are several things that you can do. First, try to locate the compressor in warmer area, then keep the refrigerant charge to the minimum requirement (refrigerant to oil ratio). You should also check the crankcase heater to make sure that it is working properly. A faulty crankcase heater, as mentioned above, can increase the possibility of liquid migration. The ultimate solution would be to try and use continuous pump down. |
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| Section 4: For More Information
More detailed compressor technical information and technical bulletins can be found in our ONLINE PRODUCT INFORMATION, which you can access through the Detailed Product Information link at the top of this page. The following bulletins found here offer more detailed information about refrigerant control and compressor operation: 4-1301, 4-1311, 4-1312, 17-1238, 17-1243, 22-1182. The Copeland Compressor Service and Operating Seminar (COSS) and Copeland's A/C Training courses can also help walk you through identifying and repairing floodback problems.
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