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COP = Energy Out Energy In COP = Btus Out Btus In

Btus Out = Btus in times COP

COP = Watts Out Watts In Btus divide 3.413 = Watts Watts times 3.413 = Btus Btus divide 3413 = Kilowatts

Bristol TS Technology Twin-Single 2 Stage Compressor

Variable Capacity Oil Return

Oil return is a major issue in variable capacity multiple evaporator systems. Current technologies use an oil separator and/or complicated oil return cycle to ensure oil return after some period of operation. The Digital Scroll is a unique compressor it does not require an oil separator or an oil return cycle. There are 2 factors that make the oil return easy. First, the oil leaves the compressor only during the loaded cycle. So at low capacities, very little oil leaves the compressor. Second, as explained before, the compressor operates at full capacity during the loaded cycle. The gas velocity in the loaded cycle is sufficient to return oil back to the compressor. Our testing has shown that oil is able to return back to the compressor even in the worst operating conditions low modulation, 100 meter pipe length and 30 meter elevation (with standard oil traps), both straight and reverse elevation.

Ultra Tech Scroll

Copeland Ultra-Tech

A piston is fixed to the top scroll to ensure that when the piston moves up, the top scroll also moves up. There is a modulation chamber at the top of the piston that is connected to the discharge pressure through a bleed hole of diameter 0.6 mm. An external solenoid valve connects the modulation chamber with the suction side pressure. When the solenoid valve is in the normally closed position, the pressure on either side of the piston is discharge pressure and a spring force ensures that the two scrolls are loaded together. When the solenoid valve is energized, the discharge gas in the modulation chamber is relieved to the low pressure. This causes the piston to move up and consequently the top scroll also moves up. This action separates the scrolls and results in no mass flow through the scrolls. Deenergizing the external solenoid valve again loads the compressor fully and the compression is resumed. It should be noted that the movement of the top scroll is very small - 1.0 mm and consequently the amount of high-pressure gas that is bled from the high side to the low side is very little.

Copeland Semi-Hermetic Screw Compressor

Three Phase Voltage Monitor

To test if the compressor is pumping properly, the compressor current draw must be compared to published compressor performance curves using the operating pressures and voltage of the system. If the average measured current deviates more than 15% from published values, a faulty compressor may be indicated. A current imbalance exceeding 15% of the average on the three phases may indicate a voltage imbalance and should be investigated further. A more comprehensive troubleshooting sequence for compressors and systems can be found in Section H of the Copeland Electrical Handbook.


Most compressors fail due to system malfunctions which must be corrected to prevent repeat failures. After a compressor fails, field examination of the failed compressor often will reveal symptoms of system problems. Proper corrections will help eliminate future failures.
REFRIGERANT FLOODBACK This is a result of liquid refrigerant returning to the compressor during the running cycle. The oil is diluted with refrigerant to the point it cannot properly lubricate the load bearing surfaces. The liquid washed the oil off the pistons and cylinders during the suction stroke causing them to wear during the compression stroke. The liquid dilutes the oil in the crankcase and the refrigerant rich oil will be pumped to the rods and the bearings through the crankshaft. As the refrigerant boils off, there will not be enough oil for sufficient lubrication at the bearings farthest from the oil pump. The center and rear bearings may seize or may wear enough to allow the rotor to drop and drag on the stator causing it to short. Correction: (1) Maintain proper evaporator and compressor superheat. (2) Correct abnormally low load conditions. (3) Install accumulators to stop uncontrolled liquid return.

IDENTIFYING COMPRESSOR MECHANICAL FAILURES FLOODED STARTS This is the result of refrigerant vapor migrating to the crankcase oil during the off cycle. When the compressor starts, the diluted oil cannot properly lubricate the crankshaft load bearing surface causing an erratic wear or seizure pattern. Correction: (1) Locate compressor in warm ambient or install continuous pump down. (2) Check crankcase heater operation. SLUGGING This is the result of trying to compress liquid refrigerant and/or oil, in the cylinders. Slugging is an extreme floodback in air cooled compressors and a severe flooded start on refrigerant cooled compressors. Correction: (1) Maintain proper evaporator and compressor superheat. (2) Correct abnormally low load conditions. (3) Install accumulators to stop uncontrolled liquid return. (4) Locate compressor in warm ambient or install continuous pump down.

IDENTIFYING COMPRESSOR MECHANICAL FAILURES HIGH DISCHARGE TEMPERATURE This is the result of temperatures in the compressor head and cylinders becoming so hot that the oil loses its ability to lubricate properly. This causes rings, pistons and cylinders to wear resulting in blow by, leaking valves, and metal debris in the oil. Correction: (1) Correct abnormally low load conditions. (2) Correct high discharge pressure conditions. (3) Insulate suction lines. (4) Provide proper compressor cooling. LOSS OF OIL This is a result of insufficient oil in the crankcase to properly lubricate the load bearing surfaces. When there is not enough refrigerant mass flow in the system to return oil to the compressor as fast at it is pumped out, there will be a uniform wearing or scoring of all load bearing surfaces. Correction: (1) Check oil failure control operation if applicable. (2) Check system refrigerant charge. (3) Correct abnormally low load conditions or short cycling. (4) Check for incorrect pipe sizes and/or oil traps. (5) Check for inadequate defrosts.

R-717 System Corrosion Failure