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 1 Suction Service Valve Inlet Valve Seat Gauge Port Packing Packing Nut Valve Stem Copyright 2006 Thomson Delmar Learning 2 Valve Position 1. Back seated • Normal position, backed out all the way Copyright 2006 Thomson Delmar Learning 3 Suction Valve “Back Seated” Copyright 2006 Thomson Delmar Learning 4 Valve Position 2. Mid-seated or “cracked” • Service position, opens gauge port Copyright 2006 Thomson Delmar Learning 5 Allows pressure reading Valve “Cracked” Copyright 2006 Thomson Delmar Learning 6 Valve Position 3. Front seated • Closes suction line, run in all the way • Compressor is isolated from system Copyright 2006 Thomson Delmar Learning 7 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 8 Discharge Valve Front Seated Compressor now ready for service, or removal. Copyright 2006 Thomson Delmar Learning 9 Solenoid Valves The next slide is a cutaway view of the valve. Following that is an exploded view. Copyright 2006 Thomson Delmar Learning 10 Solenoid Valve Magnetic Coil Plunger housing Plunger / Needle Seat Copyright 2006 Thomson Delmar Learning 11 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 12 Pump-down Solenoid Valve Magnetic coil de-energized Plunger drops Fluid stops Plunger Seat Copyright 2006 Thomson Delmar Learning 13 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 14 Solenoid Valve Installed Backward Coil de-energized, plunger is down. 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. Copyright 2006 Thomson Delmar Learning 15 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 16 Pump-down Solenoid Operation 6. LP control opens, compressor shuts off LOW PRESSURE CONTROL 4.Suction line refrigerant stored in receiver CONDENSER 5. As system pumps down suction pressure falls 2.Liquid Line Solenoid De-Energized 3.Shuts off flow of refrigerant LIQUID LINE SOLENOID TEV EVAPORATOR Copyright 2006 Thomson Delmar Learning THERMOSTAT 1. Tstat satisfied 17 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 18 Pump-down Solenoid Energized 6. Compressor starts 5. L.P. Control closes CONDENSER 4. Pressure rises 1.Temperature rises in box 3. L.L.S. opens TEV EVAPORATOR Copyright 2006 Thomson Delmar Learning 2.Tstat closes 19 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 20 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 21 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 22 Refrigeration System Components Evaporator Pressure Regulator Compressor Evaporator Condenser Metering Device EPR Copyright 2006 Thomson Delmar Learning 23 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 24 Evaporator Pressure Regulator ORI O.R.I. Valve Start-Up: Box & R22 Suction Gas @ 68 psig (40º F) Opens on Rise of Inlet Pressure Valve requirements: 68# @ 40o Maintain 33° minimum evaporator (59 psig for R22) Outlet to Compressor Valve wide open Inlet from Evaporator 68# @ 40o Copyright 2006 Thomson Delmar Learning 25 Evaporator Pressure Regulator – Design Conditions Evaporator down to 59# (33º F) Design Conditions Valve starts to close down Inlet from Evaporator 59# @ 33o Outlet to Compressor 59# @ 33o Copyright 2006 Thomson Delmar Learning 26 Adjusting the EPR • Adjust if pressure drops below 59 psig • Valve will maintain this setting Copyright 2006 Thomson Delmar Learning 27 Evaporator Pressure Regulator Adjustment Adjustment Needed 49# @ 25o Evaporator temperature continues to drop Inlet from Evaporator 49# 59# @ 33 25oo @ Copyright 2006 Thomson Delmar Learning Outlet to Compressor Valve will now maintain 59 psig no matter how low the outlet drops 28 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 29 EPR Application 25º @ 49 psig Evaporator 25º @ 49 psig Compressor tries to pull Candy Case evaporator down to 25° Candy Case 50º Box Walk-In Cooler 35º Box EPR keeps the pressure up Copyright 2006 Thomson Delmar Learning Evaporator 33º @ 59 psig 30 Sporlan Electric EPR valve Copyright 2006 Thomson Delmar Learning 31 Crankcase Pressure Regulators (CPR) by Sporlan Copyright 2006 Thomson Delmar Learning 32 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 33 Refrigeration System Valves Crankcase Pressure Regulator C.P.R. Compressor Evaporator Condenser Metering Device EPR Copyright 2006 Thomson Delmar Learning 34 Crankcase Pressure Regulator - CRO C.R.O. Valve Standard Conditions: Box & R404A Suction Gas @ 33# (0º F) Closes on Rise of Outlet Pressure 33# Outlet to Compressor Inlet from Evaporator 33# Copyright 2006 Thomson Delmar Learning 35 Hot-Pull Down • Defrost warms evaporator, pressures rise • After defrost, compressor starts • High pressures can overload compressor Copyright 2006 Thomson Delmar Learning 36 Crankcase Pressure Regulator Hot PullDown Evaporator up to 115# (55º F) Start up after defrost "Hot Pull Down" Compressor draws high current and cuts out on 115# Inlet from Evaporator overload Outlet to Compressor 115# Copyright 2006 Thomson Delmar Learning 37 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 38 Crankcase Pressure Regulator Adjustment Evaporator up to 115# (55º F) To lower outlet pressure Adjustment Needed Compressor draws normal current when pressure returns to "normal" operating range Outlet to Compressor 115# Inlet from Evaporator 115# 33# @ 0o Copyright 2006 Thomson Delmar Learning 39 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 R22 455 psig for R404A Copyright 2006 Thomson Delmar Learning 40 High Pressure Control Manual Reset Cut-out Note: Pressure has to drop at least 50 psig before it can be reset Most have Auto Reset Copyright 2006 Thomson Delmar Learning 41 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 42 Oil Separator Discharge Gas Enters Separator CONDENSER Oil is pulled into the Compressor Crankcase Discharge gas to the condenser As oil rises float opens the tube Oil is separated from the Gas Copyright 2006 Thomson Delmar Learning 43 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 44 Ranco Oil Safety Control To crankcase 1 A 120 2 240 L M To oil pump Wiring diagram Copyright 2006 Thomson Delmar Learning 45 Copeland’s Solid-state oil pressure control Pressure transducer Same terminal markings Copeland’s Solid-state oil pressure control Copyright 2006 Thomson Delmar Learning 46 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 47 Compressor and Contactor L1 Adding an Oil Safety Control L2 L3 Common wire needed for timer SENTRONIC 120v 240v Oil failure! CC Contacts open Compressor off CC Timing 2 “Times Out” CC Circuit M L 2 Alarm contacts close A 1 3 Operating Controls CC Standard compressor operation A Copyright 2006 Thomson Delmar Learning 48 “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 49 Current Sensing Relay One compressor wire through here Wires to oil control Compressor current closes relay contacts Prevents “nuisance” trips of oil control if compressor is off on internal overload Copyright 2006 Thomson Delmar Learning 50 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 51 Refrigeration System Components Receiver Compressor Evaporator + + Condenser RECEIVER Copyright 2006 Thomson Delmar Learning 52 Receiver with Top Removed 1.Liquid from condenser 5.To TEV 2.Collects in cylinder 4.Through King Valve 3.Forced up dip tube Copyright 2006 Thomson Delmar Learning 53 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 54 Receiver + King Valve + Dip Tube Copyright 2006 Thomson Delmar Learning 55 Receiver and King Valve Operation Liquid from Condenser Liquid to Evaporator The receiver stores liquid Copyright 2006 Thomson Delmar Learning Liquid is forced up the dip tube 56 King Valve Cracked to Read System Pressure Liquid from Condenser Liquid to Evaporator Copyright 2006 Thomson Delmar Learning 57 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 58 King Valve Back Seated – Normal Operation Purge Hoses Before Disconnecting Liquid level drops as liquid flows to evaporator Pssst Liquid from Condenser Liquid to Evaporator Copyright 2006 Thomson Delmar Learning 59 Suction Line Accumulator Copyright 2006 Thomson Delmar Learning 60 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 61 Suction Line Accumulator Suction Gas In Liquid boils off in the accumulator Copyright 2006 Thomson Delmar Learning Suction Gas Out Only vapor goes to compressor 62 Suction Line Accumulator Oil is returned to the compressor Oil falls to bottom of accumulator Copyright 2006 Thomson Delmar Learning OIL drawn into P-trap 63 Small Accumulator for Reach-in Freezer Small Accumulator for Reach-in Freezer Copyright 2006 Thomson Delmar Learning 64 Liquid line filter drier by Sporlan Cut-away picture of Liquid line filterdrier Copyright 2006 Thomson Delmar Learning 65 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 66 Liquid Line Filter Drier - Sporlan 100 Mesh Screen Shockproof Assembly Desiccant Core is a Blend of Molecular Sieve and Activated Alumina Copyright 2006 Thomson Delmar Learning Fiberglass Pad Strainer 67 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 68 Liquid Line Filter Drier - Sporlan - Filter Driers Clean Contaminants and Moisture from the Refrigerant Copyright 2006 Thomson Delmar Learning 69 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 70 Suction Filter Driers by Sporlan Copyright 2006 Thomson Delmar Learning 71 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 72 Copyright 2006 Thomson Delmar Learning 73 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 74 Sight Glass - Sporlan DOT MOISTURE INDICATOR Yellow indicates wet system Bubbles = Lack of refrigerant Green indicates dry system Low load Restriction Copyright 2006 Thomson Delmar Learning 75 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 76 Refrigeration System Accessories Heat Exchanger Compressor Evaporator + + Condenser RECEIVER Heat Exchanger Copyright 2006 Thomson Delmar Learning 77 Heat Exchanger Liquid In From the Receiver Liquid Out To Metering Device Liquid is cooled by suction vapor Suction Vapor To Compressor Courtesy of Packless Industries From Evaporator Ribbed Inner Pipe for Better Heat Transfer Copyright 2006 Thomson Delmar Learning 78 Heat exchanger on a Walk-in Freezer Copyright 2006 Thomson Delmar Learning 79 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 80 Vibration Eliminators Braided Wire Cover Protects Inner Pipe Copyright 2006 Thomson Delmar Learning Flexible Inner Pipe Absorbs Vibrations 81 Installation of Vibration Eliminator Must Be Installed Parallel to Compressor Crankshaft Vibration Eliminators Crankshaft Compressor Evaporator Condenser Metering Device Copyright 2006 Thomson Delmar Learning 82 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 83 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 84 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 85 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 86 Low Pressure Control As a Safety control R22 Temp Pressure 62# 35º 35º Walk-in Refrigerator, Outdoor Unit (Washington, DC winter design +10° F) 35º Tstat Cut-In Evaporator Operating Range 20º 20º Coil temp at tstat cut-out 33# 10º LP control cut-in @ +10° Normal winter design temp 17# -10º 0# -50° 42# Outdoor LP control cut-out @ -10° (20 ° below cut-in) Copyright 2006 Thomson Delmar Learning 87 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 88 Low Pressure Control As a Temperature Control Reach-in Refrigerator @ 38º Box Temperature Using a 20º TD Evaporator Coil With a TEV 66# 63# 38º 36º 39# 16º After the compressor starts the box temperature begins to drop The evaporator temperature also drops, but 20° lower than the box Compressor On Cut In Copyright 2006 Thomson Delmar Learning 89 Low Pressure Control As a Temperature Control R22 Pressure Temp 66# 60# 38º 34º Reach-in Refrigerator @ 38º Box Temperature Using a 20 º TD Evaporator Coil With a TEV Pressure and temperature continue to drop 37# 14º Compressor On Cut In 66# = 38º Copyright 2006 Thomson Delmar Learning 90 Low Pressure Control As a Temperature Control R22 Pressure Temp 35# 66# 38º 38º Reach-in Refrigerator @ 38º Box Temperature Using a 20 º TD Evaporator Coil With a TEV 5º 59# 33º Pressure and temperature fall to cut-out point 20º TD 36# 34# 13º 11º 2 # Coil Pressure Drop 2º Compressor On Cut Out 11° Cut In 38° Copyright 2006 Thomson Delmar Learning 91 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 92 Low Pressure Control As a Temperature Control R22 Pressure Temp 35# 66# 38º 38º Reach-in Refrigerator @ 38º Box Temperature Using a 20 º TD Evaporator Coil With a TEV 38º 27º 34# Compressor Off Cycle 11º 11º LP Control ready to start another cycle Compressor On Cut Out 11° Cut In 38° Copyright 2006 Thomson Delmar Learning 93
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