Learning Objectives Describe the purpose of the compressor, condenser, metering valve, and evaporator. Explain the construction of the compressor, condenser, metering valve, and evaporator. Illustrate the operation of service valves and Schrader valves. Describe the purpose and construction of a vibrasorber.
Copyright 2014 Delmar, Cengage Learning Learning Objectives (continued) Demonstrate the operation of a thermostatic expansion valve. Explain the superheat setting of the TXV. Describe the mounting location of a sensing bulb. Determine the superheat setting of the TXV. Explain the purpose of the distributor.
Describe the purpose of the receiver tank. Copyright 2014 Delmar, Cengage Learning Learning Objectives (continued) Compare the drier materials and explain the purpose of the filter dryer. Describe the purpose and operation of the heat exchanger Describe the purpose and operation of the accumulator.
Explain the purpose of pressure regulating devices. Describe the purpose and operation of the different types of refrigerant safety valves. Copyright 2014 Delmar, Cengage Learning The Four Basic Component
The Compressor The Condenser The Metering Device The Evaporator Refrigerant, the fifth basic component Copyright 2014 Delmar, Cengage Learning
Four Cylinder Compressor Copyright 2014 Delmar, Cengage Learning The Compressor
Pumps refrigerant through the system Pressurizes the vapor refrigerant Raises the temperature of the refrigerant Draws a very low suction pressure High discharge and low suction pressures help control the boiling of the refrigerant Copyright 2014 Delmar, Cengage Learning
Compressor Operation Refrigerant passes through suction throttling valve (if equipped) into compressor crankcase. Piston moves down cylinder, refrigerant is drawn in through suction reed valve. Piston moves upward, refrigerant compresses to 50:1 ratio. Compressed vapor exits through the discharge valve plate to discharge manifold.
Copyright 2014 Delmar, Cengage Learning Compressor Cycle Copyright 2014 Delmar, Cengage Learning Service Valves Located on compressor suction and discharge ports Allows service manifold connection
Can isolate the compressor for service or repairs Back seated- isolates service port Mid seat- opens service ports Front seat- isolates compressor from system Copyright 2014 Delmar, Cengage Learning Service Valves Copyright 2014 Delmar, Cengage Learning
CAUTION Care must be taken to NEVER front seat the discharge service valve while the compressor is operating. Even thought the high pressure cut-out switch might be positioned below the valve, it would not operate fast enough to prevent major damage to the compressor and prevent possible personal injury. Copyright 2014 Delmar, Cengage Learning
Schrader Service Valves Copyright 2014 Delmar, Cengage Learning Vibrasorbers Flexible suction and discharge lines Positioned at the compressor Prevent engine and compressor vibrations from reaching the copper piping of the refrigerant system
There are two types of vibrasorbers Typical discharge vibrasorbers are made up of bellows shaped stainless steel center and a covering of braided stainless steel wire Typical suction vibrasorber made up of reinforced fabric covered hoses, often using replaceable mechanical fittings Copyright 2014 Delmar, Cengage Learning Vibrasorbers
Copyright 2014 Delmar, Cengage Learning Condenser Located outside of controlled space Releases heat from controlled space to outside air Consists of copper tubing running through aluminum cooling fins Refrigerant changes state from a high pressure
hot vapor to high pressure cooler liquid Copyright 2014 Delmar, Cengage Learning Condenser Copyright 2014 Delmar, Cengage Learning Receiver Tank
Acts as storage tank for refrigerant Usually contains one or two sight glasses Usually have inlet and outlet service valve Refrigerant can be isolated between receiver and compressor for downstream service
Copyright 2014 Delmar, Cengage Learning Receiver Tank Copyright 2014 Delmar, Cengage Learning Filter Dryer Filters and dries refrigerant Located in liquid line between receiver outlet and TXV
May be between compressor and condenser May be between evaporator and compressor Three different materials commonly used 1. Silica Gel 2. Activated Alumina 3. Molecular Sieve Copyright 2014 Delmar, Cengage Learning Filter Dryer
Copyright 2014 Delmar, Cengage Learning Moisture Indicator Copyright 2014 Delmar, Cengage Learning Heat Exchanger Located in liquid line between receiver and TXV or outlet of evaporator Two important functions:
1. Subcools liquid refrigerant before TXV 2. Evaporates any liquid refrigerant before it reaches the compressor Copyright 2014 Delmar, Cengage Learning Heat Exchanger Copyright 2014 Delmar, Cengage Learning
Thermal Expansion Valve Division between high and low side of system Modulates the flow of refrigerant to the evaporator Monitors evaporator outlet temperature Internal or external equalization Copyright 2014 Delmar, Cengage Learning Thermal Expansion Valve
Copyright 2014 Delmar, Cengage Learning Thermal Expansion Valve Operation Sensing bulb pressure applied to one side of the diaphragm tries to open valve against spring pressure. Evaporator outlet or compressor suction pressure applied to the opposite side of the diaphragm helps to make the valve responsive
to compressor suction pressure. Spring pressure, which is applied to the needle assembly and diaphragm on the evaporator side, constantly tries to close the valve. Copyright 2014 Delmar, Cengage Learning Determining Superheat 1. Determine the suction pressure at the compressor suction service valve. 2. Using a refrigerant pressure temperature chart,
determine the saturation temperature at the observed pressure. 3. Measure the temperature of the suction gas at the evaporator outlet. 4. Subtract the saturated temperature read from the chart in Step 2 from the temperature measured in Step 3. The difference between the two is the superheat of the suction gas returning to the compressor. Copyright 2014 Delmar, Cengage Learning
TXV Sensing Bulb TXV sensing bulb regulates the flow of refrigerant to the evaporator Bulb is normally filled with same refrigerant used in the system Charge can be vapor or liquid Some are designed to control the maximum opening pressure of the TXV to prevent compressor slugging
Sensing bulb must have good mechanical connection with the evaporator outlet Copyright 2014 Delmar, Cengage Learning TXV Sensing Bulb (continued) Sensing bulb must be positioned on the suction line so it can monitor actual vapor or line temperature, follow manufacturers recommendations If mounted at 6 oclock, refrigerant oil can
provided insulation from true vapor temperature If mounted at 12 oclock bulb would be in direct contact with line possibly causing incorrect sensing of vapor temperature Copyright 2014 Delmar, Cengage Learning Distributor Tube Distributor and header are located between the TXV outlet and evaporator inlet
Divides the refrigerant flow into several routes to the evaporator for greater efficiency Equipped with a passage so that during the heating and defrost cycle, hot gas is pumped into the evaporator, bypassing the TXV Copyright 2014 Delmar, Cengage Learning Evaporator Receives boiling refrigerant from the distributor
As refrigerant boils it absorbs heat through the cooling fins which cools the air as it passes through them Refrigerant boils because of the pressure of the refrigerant is significantly lowered by the TXV Moist air can freeze on the fins reducing efficiency, a defrost cycle is needed to prevent this Most evaporators are constructed of copper tubing swedged into aluminum fins. Tubing configuration and number of tubes determine
the BTU rating of evaporator Copyright 2014 Delmar, Cengage Learning Evaporator Copyright 2014 Delmar, Cengage Learning Accumulator Separates liquid refrigerant from vaporous refrigerant before entering the compressor
When system is operating intermittently or as heat pump, large quantities of liquid refrigerant can pass through suction line and enter the compressor Liquid refrigerant can cause broken pistons, bent connecting rods, broken valves, blown head gaskets, and damaged bearings Accumulator normally has the capacity to hold the entire refrigerant charge to prevent compressor damage Copyright 2014 Delmar, Cengage Learning
Accumulator Copyright 2014 Delmar, Cengage Learning Accumulator Operation Liquid and vapor enter accumulator and drop to the bottom Vapor returns through U shaped tube to compressor As vapor passes U tube it picks up liquid refrigerant
and oil through metering hole in bottom of U tube To prevent to much liquid refrigerant from returning to compressor an anti-siphon hole is placed at the top of the U tube To aid in the evaporation process of the accumulator a device to heat the shell of the may be added Copyright 2014 Delmar, Cengage Learning Evaporator Pressure Regulator Evaporator pressure regulator controls evaporator
pressure regardless of compressor suction pressure The pressure setting is that which is equal to 30 to 32 degrees Fahrenheit inside the evaporator coil Oil by pass line between the base of the evaporator to the compressor suction is required This type of valve not used in many application because many cargos require the evaporator to reach very low pressures in order to obtain low box temperatures
Copyright 2014 Delmar, Cengage Learning Suction Pressure Regulator Designed to limit crankcase suction pressure during heat and defrost cycle or startup During startup when evaporator and crankcase pressures are high, valve is closed When the crankcase internal suction pressure is below the set point of the valve, it begins to open and lower evaporator pressure
As the pressure of the evaporator is lowered the valve setting, it opens still more Copyright 2014 Delmar, Cengage Learning Suction Pressure Regulator (continued) During defrost/heat cycle high pressure vapor is pumped from compressor to the distributor and evaporator, suction pressure rises. High pressure overcomes spring pressure in the valve and closes the inlet cutting off inlet
flow of refrigerant The restriction caused by the valve provides needed restriction for compressor to pump against during heat/defrost cycle Copyright 2014 Delmar, Cengage Learning Suction Pressure Regulator (continued) This process causes compressor to pump highpressure (temperature) refrigerant to evaporator for heating/defrost cycle Suction pressure regulators do not totally
restrict refrigerant flow, they do not require oil bypass line These valves are adjustable by increasing or decrease spring pressure Copyright 2014 Delmar, Cengage Learning Pressure Regulating Devices Copyright 2014 Delmar, Cengage Learning
Safety Valves Most refrigeration units with more than 1 pound of refrigerant are equipped with a pressure relieving safety device Prevent possible explosion by relieving pressure caused by fire, coil blockage, or overheating of unit 2 types currently used, spring loaded and fusible metal plug Spring loaded type has spring loaded piston that
excessive refrigerant pressure must overcome and vent through an exhaust port passage Copyright 2014 Delmar, Cengage Learning Safety Valves (continued) Piston type may have slight refrigerant leak after venting but should reseal itself Fusible metal plug work on temperature only, usually 200 to 22 degree Fahrenheit or about 415 to 450 psi
The core material is designed to melt away, allowing refrigerant to escape Once a fusible plug releases pressure they must be replaced Copyright 2014 Delmar, Cengage Learning Safety Valves Fusible Plug Spring-loaded Piston
Copyright 2014 Delmar, Cengage Learning Summary There are four main components used in a refrigeration system There are many other components that improve the efficiency of the system but not necessary From the compressor superheated refrigerant passes service valves through the vibrasorber
Vibrasorbers isolates system from vibration caused by engine and compressor Copyright 2014 Delmar, Cengage Learning Summary (continued) Refrigerant then enters the condenser and gives up heat to ambient air Refrigerant cools in the condenser and condenses from gas to liquid Liquid refrigerant then enters the receiver where it
is stored until needed Refrigerant leaves receiver and passes through the filter dryer which removes moisture and contaminants Refrigerant enters the heat exchanger which further removes heat from liquid refrigerant Copyright 2014 Delmar, Cengage Learning Summary (continued) Refrigerant enters TXV and is metered to the
distributor and then evaporator TXV balances inlet flow to outlet temperature and pressure of refrigerant so it all has time to change state from liquid to a gas before exiting evaporator Refrigerant then enters the accumulator if system is equipped Accumulator separates vapor to prevent liquid from entering the compressor Copyright 2014 Delmar, Cengage Learning
Summary (continued) Refrigerant flows from accumulator through suction line, through suction vibrasorber, through suction service valve, then through suction pressure regulator if equipped Regulator controls the load placed on the engine or electric motor Refrigerant flows out suction pressure regulator into suction side of compressor
The refrigerant is then compressed and starts the journey again Copyright 2014 Delmar, Cengage Learning
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