xdxadmin
08-31-2004, 09:14 AM
Compressor failures are often directly attributable to a lack of lubrication. If your automobile never had an oil change, the engine wear would affect your auto's performance. Imagine your car running without oil and you would expect engine failure. An adequate supply of oil must be maintained in the crankcase at all times to insure continuous lubrication.
While a refrigeration system is sealed and isolated from the atmosphere, nevertheless contaminants can be found within the oil since oil break down and acid build-up result from heat, friction, and moisture. Oil test kits are available to consider the quality of your oil. A practice of changing filter/driers whenever a system is opened is important. Preventative Maintenance (P&M) schedules should determine oil quality and should look for moisture indication and signs of unnecessary compressor heat.
Oil travels with the refrigerant. A specific Refrigerant Oil is selected by manufacturers of refrigerants and compressors for the operating conditions of a system to make certain that sufficient viscosity for the evaporator temperature while maintaining lubrication for the compressor. The oil must have properties that are compatible with the refrigerant properties.
Many refrigeration systems are designed, installed or operated in such a way to prevent proper and regular oil return to the compressor.
Since many refrigeration systems are designed, installed or operated in such a way to prevent proper and regular oil return to the compressor, when oil finally does return, too much can return at once. The compressor is designed to operate with a predetermined oil level, and to gradually receive a trickle of returning oil. Excess oil in the system can cause harm in the form of oil slugging and damage to compressor valves. In the field, it is imperative that compressors be checked for proper manufacturer recommended oil levels once normal operating conditions have been attained. An Oil Separator can be used to reduce the amount of oil that travels throughout the system.
Certain manufacturers require that all compressors over a stated horsepower, or that all compressors with an external oil pump be provided with an oil pressure safety device.
Most Oil Pressure Safety Controls (OPC) utilize a manual reset for ***urance that the compressor cannot run without oil in the crankcase, and a common range is non-adjustable at 45 seconds through 120 seconds. Oil pressure safety switches can be purchased with adjustable delays and adjustable trip points. An alarm circuit is also available for which a set of contacts close upon activation of the oil pressure safety switch. As the control circuit opens to the compressor contactor, the alarm circuit contacts close and can be used to signal technicians through use of a light or bell.
An Oil Pressure Safety Control (OPC) will not protect against every lubrication problem. Simply, it does not detect whether or not the compressor is pumping oil or a combination of oil and refrigerant. Compressor bearing problems may occur when marginal lubrication is occurring due to liquid flood back. In this case, the oil pressure safety control may not trip, and be maintaining the proper pressure setting.
Typically, an Oil Pressure Safety Control (OPC) operates by determining the presence of adequate positive pressure differential between the crankcase and the oil pump discharge. If the differential is too low to close the compressor control circuit switch, the time delay is activated. This activates a resistive heating element that thermally triggers the safety switch. After the delay period times out, the safety is tripped. The heater circuit can typically be wired for different voltages determined by where the wires are placed. Miss-wiring of the control can cause damage to the heater.
Common diagnosis notes:
Common service issues concern the wiring of an Oil Pressure Safety Control (OPC). Since the OPC is to determine oil pressure of an operating compressor, improper circuiting can cause the safety to accurately sense a loss of crankcase to oil pump pressure differential, but improperly trip the compressor if the circuit remains energized. The circuit to the OPC should be broken by the compressor contactor or controller so that when the compressor is not energized, the safety is not energized.
Similarity is found in the improper diagnosis of a 'faulty' OPC when oil pressure and crankcase to oil pump pressure differential is satisfactory, but the compressor has difficulty with the compressor thermal motor protection. An overheating compressor, for mechanical or electrical reasons, can cycle on the thermal motor protector and cause the compressor to be off while the control circuit is indicating that it is running. In this case, the OPC will trip after its time delay period since no crankcase to oil pump pressure differential was maintained. The technician will often approach the compressor, press the reset and see the compressor start. If the oil level is satisfactory, either the OPC or the oil pump is incorrectly proclaimed the culprit, even though the problem might be excessive load, incorrect voltage, pressure control chattering, or an erratic contactor contact.
There are a few primary reasons that a compressor will suffer a loss of compressor lubrication:
Not enough oil in the system.
Poor condition of the oil (i.e.: wax, deterioration, acid)
Failure of the oil pump of a blockage in the compressor oil flow such as through an internal screen. Oil pumps are not commonly known to experience failures.
Loss of oil in the compressor crankcase due to compressor short-cycling or a shortage of refrigerant in the system. The refrigerant carries the oil from the compressor with insufficient run duration to enable it to return.
Liquid slugging or flooding of the compressor crankcase with liquid refrigerant causes thinning of the oil and a loss of lubrication with the resulting low viscosity.
Logging of oil in the evaporator coil, or suction piping or especially traps, due to improper piping installation, design, or maintenance.
Insufficient refrigerant velocities can resultant in a shortage of oil return.
Hunting of the Thermostatic Expansion Valve (TXV) can cause liquid refrigerant in high load conditions, post defrost periods, or lengths of time with poor evaporative coil heat transfer (i.e. heavy frost, poor medium circulation) to exit the evaporator and encroach the compressor inlet.
Reverse-flow Hot-Gas Defrost can cause additional oil logging over time.
Restrictive oil filter.
An inoperative compressor can fill up with oil and starve the operating system compressors of oil.
Poor oil float or feed device.
XDX helps to resolve these issues. X-STREAM® and A.R.M.E.D.® technologies from XDX work together to provide an evaporator coil with a refrigerant flow regime that aids in oil return from the evaporator. Annular flow has a greater m*** velocity and the refrigerant coats the inner wall of the evaporator tubing and prevents the oil from sitting in the bottom. RAPI-DEFROST® is a hot-gas defrost method that allows for same direction of flow through out all stages of the refrigeration cycle, which prevents the logging of oil caused by reverse-flow defrost methods.
While a refrigeration system is sealed and isolated from the atmosphere, nevertheless contaminants can be found within the oil since oil break down and acid build-up result from heat, friction, and moisture. Oil test kits are available to consider the quality of your oil. A practice of changing filter/driers whenever a system is opened is important. Preventative Maintenance (P&M) schedules should determine oil quality and should look for moisture indication and signs of unnecessary compressor heat.
Oil travels with the refrigerant. A specific Refrigerant Oil is selected by manufacturers of refrigerants and compressors for the operating conditions of a system to make certain that sufficient viscosity for the evaporator temperature while maintaining lubrication for the compressor. The oil must have properties that are compatible with the refrigerant properties.
Many refrigeration systems are designed, installed or operated in such a way to prevent proper and regular oil return to the compressor.
Since many refrigeration systems are designed, installed or operated in such a way to prevent proper and regular oil return to the compressor, when oil finally does return, too much can return at once. The compressor is designed to operate with a predetermined oil level, and to gradually receive a trickle of returning oil. Excess oil in the system can cause harm in the form of oil slugging and damage to compressor valves. In the field, it is imperative that compressors be checked for proper manufacturer recommended oil levels once normal operating conditions have been attained. An Oil Separator can be used to reduce the amount of oil that travels throughout the system.
Certain manufacturers require that all compressors over a stated horsepower, or that all compressors with an external oil pump be provided with an oil pressure safety device.
Most Oil Pressure Safety Controls (OPC) utilize a manual reset for ***urance that the compressor cannot run without oil in the crankcase, and a common range is non-adjustable at 45 seconds through 120 seconds. Oil pressure safety switches can be purchased with adjustable delays and adjustable trip points. An alarm circuit is also available for which a set of contacts close upon activation of the oil pressure safety switch. As the control circuit opens to the compressor contactor, the alarm circuit contacts close and can be used to signal technicians through use of a light or bell.
An Oil Pressure Safety Control (OPC) will not protect against every lubrication problem. Simply, it does not detect whether or not the compressor is pumping oil or a combination of oil and refrigerant. Compressor bearing problems may occur when marginal lubrication is occurring due to liquid flood back. In this case, the oil pressure safety control may not trip, and be maintaining the proper pressure setting.
Typically, an Oil Pressure Safety Control (OPC) operates by determining the presence of adequate positive pressure differential between the crankcase and the oil pump discharge. If the differential is too low to close the compressor control circuit switch, the time delay is activated. This activates a resistive heating element that thermally triggers the safety switch. After the delay period times out, the safety is tripped. The heater circuit can typically be wired for different voltages determined by where the wires are placed. Miss-wiring of the control can cause damage to the heater.
Common diagnosis notes:
Common service issues concern the wiring of an Oil Pressure Safety Control (OPC). Since the OPC is to determine oil pressure of an operating compressor, improper circuiting can cause the safety to accurately sense a loss of crankcase to oil pump pressure differential, but improperly trip the compressor if the circuit remains energized. The circuit to the OPC should be broken by the compressor contactor or controller so that when the compressor is not energized, the safety is not energized.
Similarity is found in the improper diagnosis of a 'faulty' OPC when oil pressure and crankcase to oil pump pressure differential is satisfactory, but the compressor has difficulty with the compressor thermal motor protection. An overheating compressor, for mechanical or electrical reasons, can cycle on the thermal motor protector and cause the compressor to be off while the control circuit is indicating that it is running. In this case, the OPC will trip after its time delay period since no crankcase to oil pump pressure differential was maintained. The technician will often approach the compressor, press the reset and see the compressor start. If the oil level is satisfactory, either the OPC or the oil pump is incorrectly proclaimed the culprit, even though the problem might be excessive load, incorrect voltage, pressure control chattering, or an erratic contactor contact.
There are a few primary reasons that a compressor will suffer a loss of compressor lubrication:
Not enough oil in the system.
Poor condition of the oil (i.e.: wax, deterioration, acid)
Failure of the oil pump of a blockage in the compressor oil flow such as through an internal screen. Oil pumps are not commonly known to experience failures.
Loss of oil in the compressor crankcase due to compressor short-cycling or a shortage of refrigerant in the system. The refrigerant carries the oil from the compressor with insufficient run duration to enable it to return.
Liquid slugging or flooding of the compressor crankcase with liquid refrigerant causes thinning of the oil and a loss of lubrication with the resulting low viscosity.
Logging of oil in the evaporator coil, or suction piping or especially traps, due to improper piping installation, design, or maintenance.
Insufficient refrigerant velocities can resultant in a shortage of oil return.
Hunting of the Thermostatic Expansion Valve (TXV) can cause liquid refrigerant in high load conditions, post defrost periods, or lengths of time with poor evaporative coil heat transfer (i.e. heavy frost, poor medium circulation) to exit the evaporator and encroach the compressor inlet.
Reverse-flow Hot-Gas Defrost can cause additional oil logging over time.
Restrictive oil filter.
An inoperative compressor can fill up with oil and starve the operating system compressors of oil.
Poor oil float or feed device.
XDX helps to resolve these issues. X-STREAM® and A.R.M.E.D.® technologies from XDX work together to provide an evaporator coil with a refrigerant flow regime that aids in oil return from the evaporator. Annular flow has a greater m*** velocity and the refrigerant coats the inner wall of the evaporator tubing and prevents the oil from sitting in the bottom. RAPI-DEFROST® is a hot-gas defrost method that allows for same direction of flow through out all stages of the refrigeration cycle, which prevents the logging of oil caused by reverse-flow defrost methods.