Student CD for Commercial Refrigeration for A/C Technicians Chapter 6 Controls and Accessories
Copyright 2006 Thomson Delmar Learning 2 Learning Objectives Temperature controls Service valves Solenoid valves CPRs and EPRs LP and HP controls Oil separators and safety controls Receivers and accumulators Filter driers and sight glasses Heat exchangers and vibration eliminators
Copyright 2006 Thomson Delmar Learning 3 Line Voltage Thermostats Primarily used in refrigeration equipment Electro-mechanical type uses a sensing bulb and bellows to operate switching Refrigeration tstats require adjustable cut-in / cut-out differentials –Most sense air temperature –Some are used to sense coil temperature
Copyright 2006 Thomson Delmar Learning 4 Remote Bulb Electro-mechanical Thermostat MAX MIN Adjustable cut-in differential 3° to 12° Cut-out set for 25° Bulb used to sense air or coil temperature
Copyright 2006 Thomson Delmar Learning 5 Cut-in Temperature Cut-out Differential Sensing Bulb Bellows Line Voltage Freezer Tstat
Copyright 2006 Thomson Delmar Learning 6 Electronic Line Voltage Thermostats Benefits of using electronic thermostats: –Accuracy –Wide range of operating temperatures
Copyright 2006 Thomson Delmar Learning 7 Line Voltage Electronic Tstat Circuit board Thermistor This tstat is sensing evaporator temperature: Cuts-out when the coil temperature drops to 25° Cuts-in when the coil temperature rises to 37°
Copyright 2006 Thomson Delmar Learning 8 Suction Service Valve Location: –Suction side (inlet) of compressor Purposes: –Check suction pressure –Check compressor valves –Isolate compressor The following slide shows the major parts of a service valve
Copyright 2006 Thomson Delmar Learning 9 Suction Service Valve Inlet Gauge Port Valve Seat Packing Packing Nut Valve Stem
Copyright 2006 Thomson Delmar Learning 10 Valve Position 1.Back seated Normal position, backed out all the way
Copyright 2006 Thomson Delmar Learning 11 Suction Valve “Back Seated”
Copyright 2006 Thomson Delmar Learning 12 Valve Position 2. Mid-seated or “cracked” Service position, opens gauge port
Copyright 2006 Thomson Delmar Learning 13 Allows pressure reading Valve “Cracked”
Copyright 2006 Thomson Delmar Learning 14 Valve Position 3. Front seated Closes suction line, run in all the way Compressor is isolated from system
Copyright 2006 Thomson Delmar Learning 15 Discharge Service Valves Location: –Discharge side of compressor Purpose: –Check discharge pressure –Isolate compressor Caution: Never front seat the discharge valve when the compressor is running.
Copyright 2006 Thomson Delmar Learning 16 Discharge Valve Front Seated Compressor now ready for service, or removal.
Copyright 2006 Thomson Delmar Learning 17 Solenoid Valves The next slide is a cutaway view of the valve. Following that is an exploded view.
Copyright 2006 Thomson Delmar Learning 18 Plunger housing Plunger / Needle Seat Magnetic Coil Solenoid Valve
Copyright 2006 Thomson Delmar Learning 19 Solenoid Valve Operation 1.Magnetic coil energized, lifts plunger 2.Fluid lifts seat, flows through valve 3.Magnetic coil de-energized, plunger falls 4.Fluid pressure on seat helps close valve
Copyright 2006 Thomson Delmar Learning 20 Pump-down Solenoid Valve Magnetic coil de-energized Plunger drops Fluid stops Plunger Seat
Copyright 2006 Thomson Delmar Learning 21 Improper installation Flow direction marked on valve –Look for an arrow or the word “in” They will leak through if installed backward
Copyright 2006 Thomson Delmar Learning 22 Solenoid Valve Installed Backward Fluid from this direction would push up the valve seat Proper flow direction marked on the valve. Fluid pressure helps to keep seat closed during pump down. Coil de-energized, plunger is down.
Copyright 2006 Thomson Delmar Learning 23 Pump-down Solenoid In Operation 1.The tstat shuts off power to the solenoid valve. 2.The valve stops the flow of liquid to the TEV. 3.Low side refrigerant is “pumped down” into the high side of the system. 4.The low pressure control shuts off the compressor.
Copyright 2006 Thomson Delmar Learning 24 EVAPORATOR CONDENSER 1. Tstat satisfied 2.Liquid Line Solenoid De-Energized 3.Shuts off flow of refrigerant TEV 4.Suction line refrigerant stored in receiver Pump-down Solenoid Operation THERMOSTAT LIQUID LINE SOLENOID LOW PRESSURE CONTROL 5. As system pumps down suction pressure falls 6. LP control opens, compressor shuts off
Copyright 2006 Thomson Delmar Learning 25 Thermostat Energizes Solenoid 1.Power to the solenoid opens the valve. 2.Liquid refrigerant flows through the TEV. 3.Low side pressure rises. 4.The low pressure control starts the compressor.
Copyright 2006 Thomson Delmar Learning 26 EVAPORATOR CONDENSER 1.Temperature rises in box 2.Tstat closes 3. L.L.S. opens TEV 4. Pressure rises Pump-down Solenoid Energized 5. L.P. Control closes 6. Compressor starts
Copyright 2006 Thomson Delmar Learning 27 Hot Gas Bypass Used to keep suction pressure up when the evaporator load falls Protects the compressor from high compression ratios and short cycling A low pressure control opens the hot gas solenoid valve
Copyright 2006 Thomson Delmar Learning 28 On a fall in suction pressure the Hot Gas solenoid opens. The Discharge Bypass Valve acts like a TEV to lower the hot gas pressure and temperature.
Copyright 2006 Thomson Delmar Learning 29 Evaporator Pressure Regulator (EPR) valve Opens on Rise of Inlet (ORI) pressure Location: In the Suction line Senses: Evaporator pressure Purpose: Keeps evaporator pressure/temperature up Maintains set temperature of product
Copyright 2006 Thomson Delmar Learning 30 Refrigeration System Components Condenser Compressor Evaporator Metering Device Evaporator Pressure Regulator EPR
Copyright 2006 Thomson Delmar Learning 31 EPR Valve Setting The following EPR is set to maintain a minimum evaporator pressure of 59 psig On start up the pressure is 68 psig As the compressor runs the pressure falls
Copyright 2006 Thomson Delmar Learning 32 Outlet to Compressor Inlet from Evaporator 40 o 40 o O. R. I. Valve Opens on Rise of I nlet Pressure Start-Up: Box & R22 Suction 68 psig (40º F) Valve requirements: Maintain 33° minimum evaporator (59 psig for R22) Valve wide open Evaporator Pressure Regulator ORI
Copyright 2006 Thomson Delmar Learning 33 Evaporator Pressure Regulator – Design Conditions Design Conditions Evaporator down to 59# (33º F) 33 o 33 o Outlet to Compressor Inlet from Evaporator Valve starts to close down
Copyright 2006 Thomson Delmar Learning 34 Adjusting the EPR Adjust if pressure drops below 59 psig Valve will maintain this setting
Copyright 2006 Thomson Delmar Learning 35 Outlet to Compressor Evaporator Pressure Regulator Adjustment Adjustment Needed 25 o 25 o Inlet from Evaporator 33 o Evaporator temperature continues to drop Valve will now maintain 59 psig no matter how low the outlet drops
Copyright 2006 Thomson Delmar Learning 36 EPRs and Multiple Evaporators Evaporator #1: Walk-in refrigerator (25° Evaporator) Evaporator #2: Candy case (33° Evaporator) Where do you install the EPR? Near the highest temperature evaporator
Copyright 2006 Thomson Delmar Learning 37 Candy Case 50º Box EPR Application Walk-In Cooler 35º Box 49 psig Evaporator Evaporator 59 psig psig EPR keeps the pressure up Compressor tries to pull Candy Case evaporator down to 25°
Copyright 2006 Thomson Delmar Learning 38 Sporlan Electric EPR valve
Copyright 2006 Thomson Delmar Learning 39 Crankcase Pressure Regulators (CPR) by Sporlan
Copyright 2006 Thomson Delmar Learning 40 Crankcase Pressure Regulator (CPR) valve Looks like an EPR, but… –Closes on Rise of Outlet (CRO) pressure Location: –Suction line near compressor Senses: –Compressor crankcase pressure Purpose: –Keeps crankcase pressure down –Prevents compressor overload during hot pull down (after freezer defrost)
Copyright 2006 Thomson Delmar Learning 41 Crankcase Pressure Regulator Condenser Compressor Evaporator Metering Device EPR Refrigeration System Valves C.P.R.
Copyright 2006 Thomson Delmar Learning 42 Crankcase Pressure Regulator - CRO Inlet from Evaporator Outlet to Compressor 33# C. R. O. Valve Closes on Rise of O utlet Pressure Standard Conditions: Box & R404A Suction 33# (0º F)
Copyright 2006 Thomson Delmar Learning 43 Hot-Pull Down Defrost warms evaporator, pressures rise After defrost, compressor starts High pressures can overload compressor
Copyright 2006 Thomson Delmar Learning 44 Crankcase Pressure Regulator Hot PullDown Start up after defrost Evaporator up to 115# (55º F) 115# Outlet to Compressor "Hot Pull Down" 115# Compressor draws high current and cuts out on overload Inlet from Evaporator
Copyright 2006 Thomson Delmar Learning 45 Adjusting the CPR Valve Adjust when compressor is overloaded Install ammeter on the compressor Front seat suction service valve Start compressor Open suction valve until compressor draws 10% more than Run Load Amps (RLA) Adjust CPR until compressor draws RLA Back seat suction valve
Copyright 2006 Thomson Delmar Learning 46 Crankcase Pressure Regulator Adjustment 115# Inlet from Evaporator To lower outlet pressure 0 o Adjustment Needed Evaporator up to 115# (55º F) 115# Compressor draws normal current when pressure returns to "normal" operating range Outlet to Compressor
Copyright 2006 Thomson Delmar Learning 47 Pressure Controls Stop and Start current flow Energize or de-energize refrigeration components Typical pressure controls: 1.Low Pressure – Closes on rise 2.High Pressure – Opens on rise 3.Low Ambient fan control – Closes on rise 4.Oil Safety Switch – Opens on rise in differential - Has a time delay
Copyright 2006 Thomson Delmar Learning 48 Low Pressure Control When pressure falls, circuit opens. Adjusting the control shown on the next slide: 1.Set the cut-in pressure 2.Set the differential 3.The cut-out is the cut-in pressure minus the differential.
Copyright 2006 Thomson Delmar Learning 49 Low Pressure Control Differential Cut-in Example: Cut-in 50 psig Less Differential 20 psig Equals Cut-out 30 psig Normally closed contacts
Copyright 2006 Thomson Delmar Learning 50 Low Pressure Control The next control is easier to set: 1.Set the cut-in pressure 2.Set the cut-out pressure
Copyright 2006 Thomson Delmar Learning 51 Cut-out Cut-in Low Pressure Control
Copyright 2006 Thomson Delmar Learning 52 System Low Pressure Normal Operation Following slide, walk-in refrigerator: Tstat drops 5° before shutting off Coil temperature drops also Coil temperature is 10° below box temperature (Because walk-in evaporator TD is 10°)
Copyright 2006 Thomson Delmar Learning 53 Normal Cycle for a 35° Walk-in Refrigerator R22 Pressure Temp 35º62# Evaporator Operating Range 5º Drop 10º TD Evaporator Coil Tstat Cut-in Refrigerating Cycle 35º 42# 30º 20º 10º TD 20º Coil Temperature Tstat Cut-out 30º
Copyright 2006 Thomson Delmar Learning 54 Low Pressure Control for Safety Protects compressor due to loss of refrigerant Indoor condensing unit LP control cut-out: 20° below coil temperature when tstat is satisfied Cut-in is affected by ambient –Outdoor units, cut - in equal to winter design –Walk - in refrigerator example: Normal winter design temperature is +10° Cut-in should be 10 to 20 psig above cut - out Or 30° below coil temperature when tstat shuts off
Copyright 2006 Thomson Delmar Learning 55 Low Pressure Control R22 Pressure Temp 35º 24# 0# 0º0º -50º 62# 35º Walk-in Refrigerator (Indoor condensing unit) 20º 42# Evaporator Operating Range 35º Tstat Cut-In 20º Coil temp at tstat cut-out As a Safety control Coil temperature drops due to lack of refrigerant Indoor LP control 0 º (20 º below lowest evap temp)
Copyright 2006 Thomson Delmar Learning 56 LP Control on Outdoor Units Cut-out is 20° below cut-in Cut-in is affected by outdoor ambient: –Cut-in should be equal to “winter design” Following slide example: –Walk-in refrigerator located in Washington, DC –Normal winter design temperature is +10° –LP control cut-in set at +10° –LP control cut-out is 20° lower, or -10°
Copyright 2006 Thomson Delmar Learning 57 Low Pressure Control R22 Pressure Temp 35º 33# 0# 10º -50° 62# 35º Walk-in Refrigerator, Outdoor Unit (Washington, DC winter design +10° F) 20º 42# Evaporator Operating Range 35º Tstat Cut-In 20º Coil temp at tstat cut-out As a Safety control LP control +10° Normal winter design temp Outdoor LP control -10° (20 ° below cut-in) 17#-10º
Copyright 2006 Thomson Delmar Learning 58 Low Pressure Control Used as a Thermostat Thermostats sense box temperature LP Control senses pressure Pressure equals evaporator temperature LP Control is both a temperature and safety control: –Cut-in: At a pressure equal to the maximum box temperature –Cut-out: At a pressure equal to 5° below maximum box temperature, Less the coil TD Less 2° (Allowance for coil pressure drop)
Copyright 2006 Thomson Delmar Learning 59 Low Pressure Control As a Temperature Control Compressor On Reach-in 38º Box Temperature Using a 20º TD Evaporator Coil With a TEV Cut In 66# 39# 63# 38º 16º 36º After the compressor starts the box temperature begins to drop The evaporator temperature also drops, but 20° lower than the box
Copyright 2006 Thomson Delmar Learning 60 Low Pressure Control As a Temperature Control R22 Pressure Temp Compressor On Reach-in 38º Box Temperature Using a 20 º TD Evaporator Coil With a TEV Cut In 66# = 38 º Pressure and temperature continue to drop 66# 37# 60# 38º 14º 34º
Copyright 2006 Thomson Delmar Learning 61 Reach-in 38º Box Temperature Using a 20 º TD Evaporator Coil With a TEV Low Pressure Control As a Temperature Control R22 Pressure 35# Temp 38º Compressor On Cut In 38° Cut Out 11° 2 # Coil Pressure Drop 5º5º 2º2º 35# 20º TD 36#13º Pressure and temperature fall to cut-out point 38º 66# 59# 33º 34# 11º
Copyright 2006 Thomson Delmar Learning 62 Low Pressure Cuts Out, Now What? Pressure (and coil temperature) slowly rise Evaporator defrosts automatically Note: good remedy for boxes with thermostats that freeze up often
Copyright 2006 Thomson Delmar Learning 63 Reach-in 38º Box Temperature Using a 20 º TD Evaporator Coil With a TEV Low Pressure Control As a Temperature Control R22 Pressure 35# Temp 38º Compressor On Cut In 38° Cut Out 11° 35# 38º 66# 34# 11º 27º 11º 38º Compressor Off Cycle LP Control ready to start another cycle
Copyright 2006 Thomson Delmar Learning 64 High Pressure Control Protects compressor from high head –Opens compressor circuit High Pressure Control cut-out setting: –155° Condensing temperature, or –60° above normal maximum ambient Example: If normal maximum ambient is 90° Cut - out is 90°+ 60°= 150° Equivalent pressure: 382 psig for R psig for R404A
Copyright 2006 Thomson Delmar Learning 65 Manual Reset Note: Pressure has to drop at least 50 psig before it can be reset Most have Auto Reset Cut-out High Pressure Control
Copyright 2006 Thomson Delmar Learning 66 Oil Separators Location: –On the discharge line –Close to crankcase –In a warm location Purpose: –Separates oil from discharge gas –Returns oil to the compressor crankcase
Copyright 2006 Thomson Delmar Learning 67 CONDENSER Oil Separator Discharge Gas Enters Separator Oil is separated from the Gas Oil is pulled into the Compressor Crankcase Discharge gas to the condenser As oil rises float opens the tube
Copyright 2006 Thomson Delmar Learning 68 Oil Pressure Safety Control Protects compressor from lack of lubrication Operates on pressure differential: –Oil pump discharge pressure –Minus suction pressure (pump inlet) –Net Oil Pressure must be above 10 psig
Copyright 2006 Thomson Delmar Learning 69 To crankcase To oil pump Wiring diagram M L 2 1 A Ranco Oil Safety Control
Copyright 2006 Thomson Delmar Learning 70 Pressure transducer Same terminal markings Copeland’s Solid-state oil pressure control
Copyright 2006 Thomson Delmar Learning 71 Oil Pressure Control Sequence Net Oil Pressure drops below 10 psig: Contacts close to start timer If pressure is low for 120 seconds it trips reset Alarm contacts close
Copyright 2006 Thomson Delmar Learning 72 Adding an Oil Safety Control Operating Controls Timing Circuit A L 2 M SENTRONIC 120v 240v Timing Circuit “Times Out” CC Oil failure! Contacts open Compressor off Alarm contacts close L1L2 L3 Common wire needed for timer Standard compressor operation Compressor and Contactor CC A
Copyright 2006 Thomson Delmar Learning 73 “Nuisance” Trips on Oil Safety Control “Brown out”, low voltage to compressor: –Compressor goes off on internal overload –But control still has voltage –The control trips because of no oil pressure Solution: Use a current sensing relay. –If the compressor is not drawing current it shuts off voltage to the control –Now the control only trips due to oil failure, not low voltage problems
Copyright 2006 Thomson Delmar Learning 74 Prevents “nuisance” trips of oil control if compressor is off on internal overload Compressor current closes relay contacts One compressor wire through here Wires to oil control Current Sensing Relay
Copyright 2006 Thomson Delmar Learning 75 Receivers Located in the liquid line Storage tank for liquid refrigerant Sized to hold 20% more than full charge Liquid from condenser enters the top Liquid leaves from bottom through dip tube Used on systems with expansion valves
Copyright 2006 Thomson Delmar Learning 76 Refrigeration System Components Condenser Compressor Evaporator Receiver RECEIVER + +
Copyright 2006 Thomson Delmar Learning 77 1.Liquid from condenser 2.Collects in cylinder 3.Forced up dip tube 4.Through King Valve 5.To TEV Receiver with Top Removed
Copyright 2006 Thomson Delmar Learning 78 The King Valve on the Receiver Location: –Receiver outlet in liquid line Purpose: –As a service port –Used to pump down system Valve positions: 1.Cracked: check system pressure 2.Front seat: pump down system 3.Back seat: normal operation
Copyright 2006 Thomson Delmar Learning Dip Tube Receiver King Valve
Copyright 2006 Thomson Delmar Learning 80 Receiver and King Valve Operation The receiver stores liquid Liquid is forced up the dip tube Liquid to Evaporator Liquid from Condenser
Copyright 2006 Thomson Delmar Learning 81 King Valve Cracked to Read System Pressure Liquid from Condenser Liquid to Evaporator
Copyright 2006 Thomson Delmar Learning 82 King Valve Front Seated -"Pumping Down" System Refrigerant from evaporator and suction line is stored as liquid in receiver. Liquid from Condenser Vapor to Evaporator
Copyright 2006 Thomson Delmar Learning 83 Liquid from Condenser Purge Hoses Before Disconnecting King Valve Back Seated – Normal Operation Liquid level drops as liquid flows to evaporator Pssst Liquid to Evaporator
Copyright 2006 Thomson Delmar Learning 84 Suction Line Accumulator
Copyright 2006 Thomson Delmar Learning 85 Suction Line Accumulators Location: –In the suction line near compressor Purpose: –Prevent liquid from slugging compressor Operation: –Liquid boils off before getting to compressor –Any trapped oil is also returned to compressor Notes: –Should not be insulated –May have liquid line coiled in bottom –Rusting may develop leaks over time
Copyright 2006 Thomson Delmar Learning 86 Suction Gas Out Suction Gas In Liquid boils off in the accumulator Suction Line Accumulator Only vapor goes to compressor
Copyright 2006 Thomson Delmar Learning 87 Oil is returned to the compressor Suction Line Accumulator Oil falls to bottom of accumulator OIL drawn into P-trap
Copyright 2006 Thomson Delmar Learning 88 Small Accumulator for Reach-in Freezer Small Accumulator for Reach-in Freezer
Copyright 2006 Thomson Delmar Learning 89 Cut-away picture of Liquid line filter- drier Liquid line filter drier by Sporlan
Copyright 2006 Thomson Delmar Learning 90 Liquid Line Filter Driers Located in liquid line: –Close to metering device for protection, or –Close to King Valve for convenience Desiccant: –Filter material in beads or block –Removes debris, moisture, and acid
Copyright 2006 Thomson Delmar Learning 91 Liquid Line Filter Drier - Sporlan Mesh Screen Fiberglass Pad Strainer Shockproof Assembly Desiccant Core is a Blend of Molecular Sieve and Activated Alumina
Copyright 2006 Thomson Delmar Learning 92 Liquid Line Filter Driers Desiccant types: Activated Alumina –High acid removal, moderate moisture capacity Molecular Sieve –High water capacity, low acid removal Silica Gel –High water capacity only
Copyright 2006 Thomson Delmar Learning 93 Liquid Line Filter Drier - Sporlan - Filter Driers Clean Contaminants and Moisture from the Refrigerant
Copyright 2006 Thomson Delmar Learning 94 Suction Line Filter Driers Location: –In the suction line Purpose: –Remove debris, moisture, acid, and wax from system Notes: –Always install one after a compressor burnout –Check pressure drop –Do not leave in the system
Copyright 2006 Thomson Delmar Learning 95 Suction Filter Driers by Sporlan
Copyright 2006 Thomson Delmar Learning 96 When to Replace a Filter Drier Whenever the system is opened for service. When the temperature drop between filter inlet and outlet is more than 3°. When there is evidence of moisture in the system. “When in doubt, change it out.”
Copyright 2006 Thomson Delmar Learning 97 Sight Glasses Location and purpose: –In the liquid line To indicate amount of liquid refrigerant flowing –Before TEV To check for liquid to TEV –After liquid line filter-drier To check for stopped up drier Types: Plain glass –only shows refrigerant flow Sight Glass with moisture indicator –Shows refrigerant flow and moisture content
Copyright 2006 Thomson Delmar Learning 98 Sight Glass - Sporlan Bubbles = Lack of refrigerant Low load Restriction Yellow indicates wet system DOT MOISTURE INDICATOR Green indicates dry system
Copyright 2006 Thomson Delmar Learning 99 Heat Exchangers Location: –Installed in the suction line leaving the evaporator How it operates: –Heat from liquid line is transferred to the suction line Benefits: 1.Subcools liquid before entering TEV Prevents “flash gas” in TEV 2.Improves evaporator efficiency May allow use of smaller evaporator Note: A capillary tube soldered to a suction line is also a type of heat exchanger
Copyright 2006 Thomson Delmar Learning 100 Refrigeration System Accessories Condenser Compressor Evaporator Heat Exchanger RECEIVER + + Heat Exchanger
Copyright 2006 Thomson Delmar Learning 101 Heat Exchanger Liquid Out To Metering Device Liquid In From the Receiver Suction Vapor From Evaporator To Compressor Ribbed Inner Pipe for Better Heat Transfer Liquid is cooled by suction vapor Courtesy of Packless Industries
Copyright 2006 Thomson Delmar Learning 102 Heat exchanger on a Walk-in Freezer
Copyright 2006 Thomson Delmar Learning 103 Vibration Eliminator Location: –Near compressor (semi - hermetic) –In line with compressor crankshaft Purpose: –Protect tubing Construction: –Inside is like a series of bellows –Outside is woven copper wire
Copyright 2006 Thomson Delmar Learning 104 Vibration Eliminators Flexible Inner Pipe Absorbs Vibrations Braided Wire Cover Protects Inner Pipe
Copyright 2006 Thomson Delmar Learning 105 Installation of Vibration Eliminator Condenser Compressor Evaporator Metering Device Vibration Eliminators Must Be Installed Parallel to Compressor Crankshaft Crankshaft
Copyright 2006 Thomson Delmar Learning 106