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Questions and Answers
What characteristic distinguishes an open drive compressor from other types of compressors?
What characteristic distinguishes an open drive compressor from other types of compressors?
Which method of lubrication is typically found in smaller compressors?
Which method of lubrication is typically found in smaller compressors?
What will occur if only one leg of power is removed from a three-phase motor?
What will occur if only one leg of power is removed from a three-phase motor?
What is the formula for calculating the compression ratio?
What is the formula for calculating the compression ratio?
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What is the primary purpose of an internal or external overload in a motor?
What is the primary purpose of an internal or external overload in a motor?
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Which cooling method involves circulating water around the compressor housing?
Which cooling method involves circulating water around the compressor housing?
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What condition can cause motor windings to deteriorate due to moisture pollution?
What condition can cause motor windings to deteriorate due to moisture pollution?
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What happens to compressor oil in high moisture environments?
What happens to compressor oil in high moisture environments?
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What is the primary function of a compressor in a refrigeration system?
What is the primary function of a compressor in a refrigeration system?
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Which component is considered the driving force of a reciprocating compressor?
Which component is considered the driving force of a reciprocating compressor?
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What distinguishes a scroll compressor from other compressor types?
What distinguishes a scroll compressor from other compressor types?
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In what way does a screw compressor differ from a reciprocating compressor?
In what way does a screw compressor differ from a reciprocating compressor?
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What happens if the compression ratio in a scroll compressor becomes too high?
What happens if the compression ratio in a scroll compressor becomes too high?
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Which of the following is a characteristic of a centrifugal compressor?
Which of the following is a characteristic of a centrifugal compressor?
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What defines a semi-hermetic compressor housing?
What defines a semi-hermetic compressor housing?
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Which type of compressor is typically used in large commercial industrial systems?
Which type of compressor is typically used in large commercial industrial systems?
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Which strategy is NOT used to prevent flooded starts in compressors?
Which strategy is NOT used to prevent flooded starts in compressors?
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What primarily causes an increase in temperature during the compression process?
What primarily causes an increase in temperature during the compression process?
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What is the correct role of the compressor in a refrigeration system?
What is the correct role of the compressor in a refrigeration system?
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Which statement accurately describes the transition of refrigerant from vapor to liquid?
Which statement accurately describes the transition of refrigerant from vapor to liquid?
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How does compression affect molecular velocity and temperature of refrigerant?
How does compression affect molecular velocity and temperature of refrigerant?
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What is the primary role of superheat in a compressor system?
What is the primary role of superheat in a compressor system?
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Which type of compressor has a separate motor component connected to it?
Which type of compressor has a separate motor component connected to it?
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What can cause compressor overheating?
What can cause compressor overheating?
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What is the effect of a larger compression ratio on a compressor?
What is the effect of a larger compression ratio on a compressor?
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Which situation might lead to flooded starts in a compressor?
Which situation might lead to flooded starts in a compressor?
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What is a critical factor for cooling most compressors?
What is a critical factor for cooling most compressors?
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How does oil circulate within the compressor system?
How does oil circulate within the compressor system?
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What defines a hermetic compressor?
What defines a hermetic compressor?
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Study Notes
Compressors I - Learning Objectives
- Demonstrate knowledge of compressors, their components, and operation
- Demonstrate knowledge of the fundamental principles of compressors
Heart of the System
- The compressor is the heart of the refrigeration system
- It creates a pressure difference, allowing refrigerant to flow from high pressure to low pressure
- It increases suction pressure to discharge pressure, e.g., 5 PSIG suction pressure to 170 PSIG discharge pressure, a 165 PSIG pressure increase
- Liquid is not compressible; compressors pump vapor
Positive Displacement
- Most compressors are positive displacement type
- A compressor draws suction vapor into a cylinder/chamber
- Reducing chamber volume increases vapor pressure and temperature through compression
Reciprocating Compressor Basics
- Positive displacement
- Piston creates pressure
- Crankshaft drives the piston
- Connecting rod transfers rotational motion to linear motion
- Not the most efficient due to clearance volume
Scroll Compressor Basics
- Fixed scroll stays stationary and attached to compressor body
- Orbiting scroll orbits during operation, creating compression
- Discharge check valve stops refrigerant from entering during the off cycle
- Handles small liquid amounts because the orbiting scroll can lift axially
- Orbiting scroll also separates axially if compression ratio is too high
Rotary Compressor Basics
- Crankshaft fully rotates rollers unlike scroll that orbits
- Vane separates high and low sides in compression chamber
- Positive displacement
Screw Compressor Basics
- Instead of a piston and cylinder, two screw type gears squeeze refrigerant vapor
- Positive displacement
- Used in large commercial/industrial systems
Centrifugal Compressor Basics
- Non-positive displacement
- Compresses refrigerant using an impeller that spins refrigerant outward
- Inlet guide vanes draw gas into the impeller center
- Impeller spins gas outward with centrifugal force
Semi Hermetic Housing
- Semi hermetic- serviceable
- Bolt on heads allow for gasket and plate replacement
Hermetic Housing
- Hermetic compressor housing is welded
- Also known as tin can type compressor
- Usually never repaired, only replaced
Open Drive Compressor
- Open drive compressor is mechanically sealed
- Drive motor is attached to the shaft end
- Designed to be repaired
- Needs shaft seal
- Can be belt or direct drive
Motor Windings Single Phase (PS)
- Start, Common, Run windings
- Start to run reading has highest resistance
- Start to common has second-highest resistance
- Run to common has lowest resistance
- Start to common + run to common = start to run
Motor Windings PSC
- 6 ohms (2nd highest) - Start
- 7.5 ohms (highest) - Common
- 1.5 ohms (lowest) - Run
Internal/External Overloads
- Internal/external overloads break common winding, killing power to motor
- Resistance readings from start to run, but OL from R to C or S to C
Motor Windings 3 Phase
- All resistance values from each winding are equal (e.g., T1 to T2 = 1.8 ohms, T2 to T3= 1.8 ohms, T1 to T3= 1.8 ohms)
- Overloads break each leg of power, single phasing and damage if a leg is removed
Compression Ratio
- Absolute Discharge / Absolute Suction
- Discharge pressure + 14.7 PSI = absolute discharge
- Suction pressure + 14.7 PSI = absolute suction
- Higher ratio requires more work for the compressor to move the refrigerant
- Example: 418 PSIG discharge, 118 PSIG suction, ratio is 3.2:1
Splash Lubrication
- Found in smaller compressors without oil pumps/delivery systems
- Compressor oil is splashed around by using crankshaft/connecting rods to scoop oil from sump
Oil Pump Feed System
- Used in larger compressors
- Pump used to force feed oil
- Lubricates bearings, crankshaft/connecting rods
- Typically mounted to the end of the compressor crankshaft
- Can be electronically driven
Cooling the Compressor
- Suction gas returning to the compressor cools motor
- Air cooled uses a fan blowing air over the compressor housing
- Water cooled uses copper coil piping around the compressor housing with water circulating to cool the compressor
Common Electrical Failures
- Shorted/grounded winding
- Moisture contamination (oil turns acidic and eats motor windings) - proper evacuation is critical
- Overheating of motor windings due to lack of suction gas
- Example: T1 to G = 142 ohms
Common Mechanical Failures
- Oil return issues resulting in mechanical failure
- Springs in reciprocating compressors causing motor knock
- Reed valves faulty, causing high discharge pressure into low-pressure suction chamber
- Scroll plate wearing from lack of oil
- Discharge check valve worn, causing flooded starts
Compressors Recap
- Air Conditioning Compressor Basics
- Diagnosing a Locked Compressor 3D
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Description
This quiz covers the fundamental principles and components of compressors, focusing on their operation and significance within refrigeration systems. Understand the functionality of positive displacement compressors and the mechanics behind reciprocating compressors.
