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BASIC REFRIGERATION & CHARGING PROCEDURES. SECTION ONE. REFRIGERANT PRESSURES, STATES & CONDITIONS. Load out to ambient. Load in from house. Heat flows from hot to cold. Evaporator Side Terms. Evaporating Pressure. Low Side Pressure. Suction Pressure. Back Pressure.
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BASIC REFRIGERATION & CHARGING PROCEDURES
SECTION ONE REFRIGERANT PRESSURES, STATES & CONDITIONS
Load out to ambient Load in from house
Evaporator Side Terms • Evaporating Pressure • Low Side Pressure • Suction Pressure • Back Pressure
Condenser Side Terms • Condensing Pressure • Head pressure • High side pressure • Discharge pressure
Compressor • Pumps refrigerant vapor only! • Divides low and high side.
Discharge Line • Connects the compressor to the condenser.
Condenser • Rejects heat from the refrigerant.
Liquid Line • Supplies liquid refrigerant from the condenser to the metering device.
Metering Device • Controls the flow of refrigerant. • Divides low and high side.
Evaporator • Absorbs heat into the refrigerant. • Removesmoisture from the air
Suction Line • Returns superheated vapor from the evaporator to the compressor
Receiver • An accessory added in the liquid line to store refrigerant for different loads placed on the system.
CONDENSER Temperatures Pressures States
CONDENSER INLET • High Pressure • High Temperature • Superheated Vapor • Saturation Point (vapor changing to a liquid as heat is removed) • Near Ambient Temperature • High Pressure • Subcooled Liquid OUTLET
EVAPORATOR Temperatures Pressures States
Evaporator inlet Low Pressure Low Temperature About 80% Liquid, 20% Vapor Saturated vapor (Temperature in which liquid is changing to a vapor) • Low Pressure Low Temperature Superheated Vapor Evaporator Outlet
SECTION TWO SUBCOOLING & SUPERHEAT
Subcooling and Superheating The concepts of subcooling and superheating are the two most important principles that the service technician must understand before attempting to systematically troubleshoot hvac/r systems.
210 psig = 105 ºF -100 ºF Subcooling 5 ºF R-22 Condenser Subcooling
TOTAL SUBCOOLING 210 psig = 105 ºF -95 ºF Subcooling 10 ºF
Superheat Superheat is any heat added to completely saturated vapor that results in a rise in temperature (sensible heat change) of the gas.
60 °F 76 psig = 45 °F 15 °F superheat Evaporator Superheat
Total or System Superheat Suction line Temperature 60°F 76 psig = 45°F Superheat 15°F
SECTION THREE METERING DEVICES
Thermostatic Expansion Valve CapillaryTube Automatic Expansion Valve Fixed –Bore Piston
CapillaryTubes • Low Cost device • Have no moving parts • Can be used on a wide range of applications
Thermostatic Expansion Valve • Most efficient • Maintains a constant evaporator superheat • Helps prevent compressor flooding
TXV Types • Pressure Limiting • Balance Port • Externally equalized • Internally Equalized • Electric operated
Automatic Expansion Valves • Maintain a constant evaporator pressure • Used on small systems which have constant loads
Fixed-Bore Metering Devices • Most common today on Residential systems • Dual purpose device Works as metering a device Works as a check valve • Critical charge
SECTION FOUR System CHARGE
Is The Refrigerant Charge Correct? • All refrigeration systems differ in the amount of charge they hold. • There are guidelines, charts, and techniques to follow. • System design & layout must be known
How long & what size is the line set? What’s the volume of the filter drier?
TXV CHARGING RULES 1. Charge system under a high load 2. Charge as a liquid when possible 3. Throttle liquid blends into low side 4. Record evaporator & compressor superheat & Condenser subcooling
AIRCONDITIONING SYSTEMS Capillary Tube or Fixed Orifice #1 Weigh in the correct charge #2 Manufacture's charging charts #3 Use system superheat method
Requirements for system superheat charging • Proper evaporator air flow • Accurate remote bulb temperature tester • Accurate gauge manifold set
System Superheat Suction line Temperature 60 °F 76 psig = 45 °F Superheat 15 °F
AIR FLOW Can be measured in many ways 1. Equipment data charts 2. Air flow meters 3. Combination of meter readings and formulas
Sensible Heat Formula Sensible heat BTU’s CFM = 1.08 X temperature difference
Sensible Heat Formula Electric Heat BTU’s = Heater amps X volts X 3.41 Sensible heat BTU’s CFM = 1.08 X temperature difference
Sensible Heat Formula 3 Phase Electric Heat BTU’s = Heater amps X volts X 3.41 X 1.73 Sensible heat BTU’s CFM = 1.08 X temperature difference
Sensible Heat Formula Fossil Fuel Heat BTU’s = Heater input X Efficiency or Bonnet capacity Sensible heat BTU’s CFM = 1.08 X temperature difference
Measuring Duct Velocity CFM = Velocity X Area in square feet
SAMPLE QUESTIONS
The high and low pressures in a refrigeration system are separated by: a. The compressor. b. The evaporator. c. The metering device. d. The filter drier. The metering device.