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AIR CONDITIONING & HEAT PUMP SYSTEMS

A/C - HEAT PUMP CONTROLS & SWITCHES
A/C DATA TAGS
A/C - HEAT PUMP CRITICAL DEFECTS
A/C DIAGNOSTIC FAQs
A/C REFRIGERANTS
A/C TYPES, ENERGY SOURCE
AGE of AIR CONDITIONERS & HEAT PUMPS

AIR CONDITIONER BTU CHART
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR CONDITIONER NOT WORKING

AIR FILTERS for HVAC SYSTEMS
  Air Filter Accessibility
  Air Filter Bypass Leakage
  Air Filter Installation Procedure
  Build Large Air Filters
  Air Filter Location
  Dirty Air Filter Problems
  ENERGY SAVINGS by AIR FILTERS
  Air Filtering Strategies
  Missing or Leaky Air Filters
  AIR FILTERS, OPTIMUM INDOOR
  CONTINUOUS BLOWER FAN OPERATION
  AIR FILTER EFFECTIVENESS
  FIBERGLASS & AIR FILTERS
  SOURCES FOR AIR FILTERS
  OTHER AIR CLEANERS

AIR HANDLER / BLOWER UNITS
  ADDING A/C: RETROFIT SIZING
  BLOWER FAN CONTINUOUS OPERATION
  BLOWER FAN OPERATION & TESTING
  BLOWER LEAKS, RUST & MOLD
  COOLING COIL or EVAPORATOR COIL
  DAMAGED COOLING COIL
  DIRTY A/C BLOWERS
    Leaks, Rodents In Air Handlers
    Mold Growth in Air Handlers
  DIRTY COOLING COIL
  DIRTY COIL CLEANING PROCEDURES
  FROST BUILD-UP on AIR CONDITIONER COILS
APPLIANCE EFFICIENCY RATINGS
BACKUP HEAT for HEAT PUMPS

BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING

BOOKSTORE - Air Conditioning "How To" Books

CAPACITORS for HARD STARTING MOTORS
CAPILLARY TUBES
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
COMBUSTION GASES & PARTICLE HAZARDS

COMPRESSOR & CONDENSING COIL, A/C

CONDENSATE HANDLING, A/C
CONDENSATION or SWEATING PIPES, TANKS
CONDENSING COIL
COOL OFF HEAT Thermostat Switch
COOLING CAPACITY, RATED
COOLING COIL or EVAPORATOR COIL
COOLING LOAD REDUCTION by ROOF VENTS
DATA TAGS on AIR CONDITIONERS
COMBUSTION GASES & PARTICLE HAZARDS
CONDENSING BOILERS/FURNACES
CONDENSING BOILERS/FURNACES DAMAGE
COOLING COIL or EVAPORATOR COIL
COOLING LOAD REDUCTION by ROOF VENTS
CRITICAL DEFECTS on A/C SYSTEMS

DATA TAGS on AIR CONDITIONERS
DEFINITION of Heating & Cooling Terms

DEHUMIDIFICATION PROBLEMS
  CONDENSATION or SWEATING PIPES, TANKS

DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE

DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP

DUCT SYSTEM & DUCT DEFECTS
DUCTS - Asbestos
  AIR FILTERS for HVAC SYSTEMS
  ALLOY SYSTEMS FLEXDUCT
  ASBESTOS HVAC DUCTS
  ASBESTOS PAPER on DUCTWORK
  ASBESTOS TRANSITE DUCTWORK
  BALANCING AIR DUCT FLOW
  DUCT & AIR HANDLER ODORS
  DUCT DAMAGE, MECHANICAL
  DUCT INSULATION - Asbestos Paper
  DUCT ROUTING & SUPPORT
  DUST CONTAMINATION FROM HVAC?
  FIBERGLASS DUCT, RIGID CONSTRUCTION
  FIBERGLASS HVAC DUCTS
  FIRE DAMPERS in DUCTWORK
  FLOOD DAMAGE in DUCT WORK
  GOODMAN GRAY FLEXDUCT
  INCREASING RETURN AIR
  LEAKY DUCT CONNECTIONS
    Leaky or Missing Air Ducts
    Hidden Missing Air Conditioner Duct
    Duct Retrofit Leaks
    Rooftop Duct Leaks
    RETURN DUCT AIR LEAKS
    SUPPLY DUCT AIR LEAKS
  LOCATION OF REGISTERS & DUCTS
  MOLD in AIR HANDLERS & DUCT WORK
  NOISES in DUCT SYSTEM
  ODORS in AIR HANDLERS & DUCT WORK
  OWENS CORNING FLEXDUCT
  OWL FLEXDUCT
  RETURN AIR REGISTERS & DUCTS
  SOUNDPROOFING for DUCTWORK
  SUPPLY DUCTS & REGISTERS
  TRANSITE PIPE AIR DUCTS
  UNDERSIZED RETURN DUCTS
  UNSAFE DUCT OPENINGS
  VIBRATION DAMPENERS
  WATER & ICE IN DUCT WORK
  WET CORRODED DUCT WORK
  ZONE DAMPER CONTROLS

DUST CONTAMINATION FROM HVAC?

EDUCATION, HVAC SCHOOLS
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRICAL POWER SWITCH FOR HEAT

ENERGY SAVINGS in buildings
EVAPORATIVE COOLING SYSTEMS
EVAPORATOR COIL or COOLING COIL
EXPANSION VALVES, REFRIGERANT

FAN, AIR HANDLER BLOWER UNIT
FAN AUTO ON Thermostat Switch
FAN CONVECTOR HEATERS - HYDRONIC COILS
FAN LIMIT SWITCH
FAN NOISES

FURNACES WARM AIR HEATING SYSTEMS

GASES, EXPOSURE, TESTING
  Carbon Dioxide - CO2
  Carbon Monoxide - CO
  METHANE GAS SOURCES
GAS MEASUREMENT TOOLS
GAUGE, REFRIGERATION PRESSURE TEST

HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION

HEAT PUMPS
HEATING SMALL LOADS
HOUSEWRAP AIR & VAPOR BARRIERS

HUMIDITY LEVEL TARGET

INDOOR AIR QUALITY IMPROVEMENT GUIDE

INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS
LEED GREEN BUILDING CERTIFICATION

LOST COOLING CAPACITY

MANUALS & PARTS GUIDES - HVAC
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK

ODORS in AIR HANDLERS & DUCT WORK
OPERATING COST
OPERATING DEFECTS
OPERATING TEMPERATURES

NOISY AIR CONDITIONER / HEAT PUMP
NOISE / SOUND DIAGNOSIS & CURE
  Air Leak Noises
  AIR CONDITIONING & HEAT PUMP NOISES

PORTABLE ROOM AIR CONDITIONERS
PRESSURE READINGS, REFRIGERANT

REPAIR GUIDE, AIR CONDITIONERS / HEAT PUMPS
REPAIR & DIAGNOSTIC FAQs for A/C

REFRIGERANTS
RETROFIT SIZING for A/C or HEAT PUMPS

SEER RATINGS & OTHER DEFINITIONS
  SEER RATING HISTORY

SOLAR ENERGY SYSTEMS

SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS
SWAMP COOLERS
SYSTEM OPERATION
  OPERATING CONTROLS
  SAFETY CONTROLS

THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES

WATER COOLED AIR CONDITIONERS

More Information

Photograph of an inadequate, mis-located single return air duct for a building apartment. Return Air Registers & Ducts for Heating / Cooling Systems
InspectAPedia®  -    

  • Defects in return air ducts & registers for heating or cooling systems
  • Return air adequacy
  • Air Conditioning (or Heating) Return Air & Duct Defects
  • Questions & answers about HVAC system return air or "makeup air" and its effect on warm or cool air delivery in the building

This HVAC ductwork article describes the inspection of the defects in return air registers & ducts for heating or cooling systems (HVAC) to help detect duct defects like missing air conditioning cool air supply or return air registers, undersized air conditioning duct openings, improper cooling duct routing, cooling (or heating) air duct corrosion, leaky air duct connections, defective heating or cooling ductwork materials.

InspectAPedia offers impartial, unbiased advice without conflicts of interest. We will block advertisements which we discover or readers inform us are associated with bad business practices, false-advertising, or junk science. Our contact info is at InspectAPedia.com/Contact.htm.

The photograph above shows a single central return air duct located outside of the apartment which the duct system intends to serve. This installation prevents recirculating of air through the air handler for heating or cooling and results in poor air flow and increased heating and cooling costs for the apartment owners. Also see our safety warnings at INCREASING RETURN AIR.

© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

The master document, of which this is a chapter, describes the inspection of residential air conditioning systems (A/C systems) to inform home buyers, owners, and home inspectors of common cooling system defects.

Steps to Inspect, Diagnose, & Improve Heating or Cooling Return Air Flow

Basement Air Handler, No Return Air Ducts, All Return Air Taken at Air Handler

Photograph of one-way return air on basement AHU also may draw flue gases from nearby gas fired equipment Photograph of one-way return air on basement AHU also may draw flue gases from nearby gas fired equipment

One-Way Cooling or Heating Systems: Some retrofit HVAC installers simply cannot figure out where to place return ducts, so they are just omitted such as shown in the two photographs here. For example a basement or crawl space air handler may be found with no return duct connections at all.

Rather you'll see that the return plenum is simply open to the basement or crawl space. The second photograph confirms that wet, possibly moldy debris enters the HVAC system at this single point basement air return to the blower unit. In the foreground of the photograph you can see our Burkard (TM) air sampling machine being used to take a look at what the basement is sending into the home's ductwork and living space.

This forms a "one way" cooling or heating system - 100% of the air is drawn from the area around the air handler, cooled (or heated) and blown "one way" into the occupied space. This is the most inefficient design possible as well as possibly a dangerous one (see "Flue Gases" above).

Preferably return air is drawn from the heated or cooled space. Taking "new" makeup air from an unheated space, heating it, and blowing it "one way" into the heated area has to be a more costly way to heat a building. For better indoor air quality and as recommended by ASHRAE, commercial and large residential heating and cooling systems may include apportion of outdoor fresh air input to the duct system as well.

Attic Air Handler Air Conditioner Return Duct Defects

Photograph of one-way return air on basement AHU also may draw flue gases from nearby gas fired equipment

This photograph shows a typical black, large-diameter return flex-duct moving building air to the air conditioning system air handler unit located in an attic.

Notice the loose fiberglass insulation around the base of the large-diameter black flex-duct carrying return air? Poor connections at this location were pulling loose fiberglass insulation fragments and attic dust and debris into the air handler system.

In addition, this poor return duct connection, by leaking attic air into the duct system, increased the air conditioning operating cost by feeding it hot attic air instead of building living space air.

This photograph has a couple of other interesting details. Notice that the return duct is partly crimped and thus obstructed as it passes through the site-built building truss?

Also, what's that electric motor doing lying askew in the insulation next to the flex-duct? Perhaps the central air return, located in the ceiling of the space below, was placed where previously there had been a ceiling-mounted whole house fan, for which we see the motor, abandoned in the attic floor.

Understanding the history of changes made to a building can help interpret the meaning of clues about the building condition. It would be a safer practice to remove the still-connected but un-used fan motor.

Either remove the un-used fan circuit wiring completely, or enclose the termination of the un-used wires in a junction box.

HVAC Return Air Duct Leaks & Obstructions - Theory & Practice

Technical note: The D'Arcy-Weisbach equation for pressure and head loss can be used to calculate the actual pressure loss due to friction in a building piping or air duct system. The Engineering Toolbox provides the D'Arcy-Weisbach formula: Δp = λ (l / dh) (ρ v2 / 2)  where Δp = pressure loss (Pa, N/m2), and l = length of duct or pipe (m) and dh = hydraulic diameter (m) and finally, ρ = density (kg/m3).

Watch out: But keep in mind that even this apparently accurate calculation of the effect of piping on air pressure and airflow loss will not include the effects of obstructions in the building return air or supply air duct system such as

  • Air filter or other item that has been sucked into the duct system will block air flow and can risk a fire if drawn into the blower assembly fan, Dirty Air Filter Problems are perhaps the most common cause of unsatisfactory airflow in an HVAC system.
  • Blower Fan: dirty blades on a squirrel cage blower assembly fan significantly reduce the blower fan's ability to move air into the HVAC system from the return-air side as well as reducing its ability to push conditioned air into the occupied space. DIRTY A/C BLOWERS
  • Fire damper that has become stuck in the closed or partly-closed position interferes with proper airflow through the system FIRE DAMPERS in DUCTWORK
  • Flex duct defects: Collapsed sections of flex duct block or stop airflow in either supply or return air systems DUCT ROUTING & SUPPORT
  • Insulation loose in air ducts: Collapsed duct interior insulation, (FIBERGLASS DUCT, RIGID CONSTRUCTION
  • Leaks in the supply air duct system are a very common HVAC duct defect that results in poor heating or cooling air flow. LEAKY DUCT CONNECTIONS
  • Return air inlets: Return air inlet grilles that are obstructed with dirt, debris, or furniture or that are improperly located or are just too small mean that because the heating or cooling system is "starved for air", the supply air flow into occupied spaces will also be reduced. RETURN AIR REGISTERS & DUCTS
  • Transite air ducts: Crushed or collapsed transite duct TRANSITE PIPE AIR DUCTS
  • Zone dampers that are stuck partly closed obstruct air supply into that building area, or if stuck "open" when the zone damper should be closed, airflow to other building areas will be reduced. ZONE DAMPER CONTROLS
  • Also see UNDERSIZED RETURN DUCTS.

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  • InspectAPedia.com® - Daniel Friedman - Publisher & Editor.
  • InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also include a list of recommended books for the specific article topic as well as other references, and information sources.
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  • Additional technical contributors & reference sources for this article are listed below.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

AIR CONDITIONING & HEAT PUMP SYSTEMS
AIR FILTERS for HVAC SYSTEMS
  Air Filter Accessibility
  Air Filter Bypass Leakage
  Air Filter Installation Procedure
  Build Large Air Filters
  Air Filter Location
  Dirty Air Filter Problems
  ENERGY SAVINGS by AIR FILTERS
  Air Filtering Strategies
  Missing or Leaky Air Filters
  AIR FILTERS, OPTIMUM INDOOR
  CONTINUOUS BLOWER FAN OPERATION
  AIR FILTER EFFECTIVENESS
  FIBERGLASS & AIR FILTERS
  SOURCES FOR AIR FILTERS
  OTHER AIR CLEANERS

AIR HANDLER / BLOWER UNITS
  ADDING A/C: RETROFIT SIZING
  BLOWER FAN CONTINUOUS OPERATION
  BLOWER FAN OPERATION & TESTING
  BLOWER LEAKS, RUST & MOLD
  COOLING COIL or EVAPORATOR COIL
  DAMAGED COOLING COIL
  DIRTY A/C BLOWERS
    Leaks, Rodents In Air Handlers
    Mold Growth in Air Handlers
  DIRTY COOLING COIL
  DIRTY COIL CLEANING PROCEDURES
  FROST BUILD-UP on AIR CONDITIONER COILS
APPLIANCE EFFICIENCY RATINGS
BACKUP HEAT for HEAT PUMPS

BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING

BOOKSTORE - Air Conditioning "How To" Books

CAPACITORS for HARD STARTING MOTORS
CAPILLARY TUBES
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
COMBUSTION GASES & PARTICLE HAZARDS

COMPRESSOR & CONDENSING COIL, A/C

CONDENSATE HANDLING, A/C
CONDENSATION or SWEATING PIPES, TANKS
CONDENSING COIL
COOL OFF HEAT Thermostat Switch
COOLING CAPACITY, RATED
COOLING COIL or EVAPORATOR COIL
COOLING LOAD REDUCTION by ROOF VENTS
DATA TAGS on AIR CONDITIONERS
COMBUSTION GASES & PARTICLE HAZARDS
CONDENSING BOILERS/FURNACES
CONDENSING BOILERS/FURNACES DAMAGE
COOLING COIL or EVAPORATOR COIL
COOLING LOAD REDUCTION by ROOF VENTS
CRITICAL DEFECTS on A/C SYSTEMS

DATA TAGS on AIR CONDITIONERS
DEFINITION of Heating & Cooling Terms

DEHUMIDIFICATION PROBLEMS
COOLING LOAD REDUCTION by ROOF VENTS

DEHUMIDIFICATION PROBLEMS
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE

DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP

DUCT SYSTEM & DUCT DEFECTS
DUCTS - Asbestos
  AIR FILTERS for HVAC SYSTEMS
  ALLOY SYSTEMS FLEXDUCT
  ASBESTOS HVAC DUCTS
  ASBESTOS PAPER on DUCTWORK
  ASBESTOS TRANSITE DUCTWORK
  BALANCING AIR DUCT FLOW
  DUCT & AIR HANDLER ODORS
  DUCT DAMAGE, MECHANICAL
  DUCT INSULATION - Asbestos Paper
  DUCT ROUTING & SUPPORT
  DUST CONTAMINATION FROM HVAC?
  FIBERGLASS DUCT, RIGID CONSTRUCTION
  FIBERGLASS HVAC DUCTS
  FIRE DAMPERS in DUCTWORK
  FLOOD DAMAGE in DUCT WORK
  GOODMAN GRAY FLEXDUCT
  INCREASING RETURN AIR
  LEAKY DUCT CONNECTIONS
    Leaky or Missing Air Ducts
    Hidden Missing Air Conditioner Duct
    Duct Retrofit Leaks
    Rooftop Duct Leaks
    RETURN DUCT AIR LEAKS
    SUPPLY DUCT AIR LEAKS
  LOCATION OF REGISTERS & DUCTS
  MOLD in AIR HANDLERS & DUCT WORK
  NOISES in DUCT SYSTEM
  ODORS in AIR HANDLERS & DUCT WORK
  OWENS CORNING FLEXDUCT
  OWL FLEXDUCT
  RETURN AIR REGISTERS & DUCTS
  SOUNDPROOFING for DUCTWORK
  SUPPLY DUCTS & REGISTERS
  TRANSITE PIPE AIR DUCTS
  UNDERSIZED RETURN DUCTS
  UNSAFE DUCT OPENINGS
  VIBRATION DAMPENERS
  WATER & ICE IN DUCT WORK
  WET CORRODED DUCT WORK
  ZONE DAMPER CONTROLS

  • Thanks to Mark Cramer, Tampa Florida, for assistance in technical review of the "Critical Defects" section and for the photograph of the deteriorating gray Owens Corning flex duct in a hot attic. Mr. Cramer is a Florida home inspector and home inspection educator.
  • Thanks to Jon Bolton, an ASHI, FABI, and otherwise certified Florida home inspector who provided photos of failing Goodman gray flex duct in a hot attic.
  • Air Diffusion Council, 1901 N. Roselle Road, Suite 800, Schaumburg, Illinois 60195, Tel: (847) 706-6750, Fax: (847) 706-6751 - info@flexibleduct.org - www.flexibleduct.org/ -
    "The ADC has produced the 4th Edition of the Flexible Duct Performance & Installation Standards (a 28-page manual) for use and reference by designers, architects, engineers, contractors, installers and users for evaluating, selecting, specifying and properly installing flexible duct in heating and air conditioning systems.
    Features covered in depth include: descriptions of typical styles, characteristics and requirements, testing, listing, reporting, certifying, packaging and product marking.
    Guidelines for proper installation are treated and illustrated in depth, featuring connections, splices and proper support methods for flexible duct. A single and uniform method of making end connections and splices is graphically presented for both non-metallic and metallic with plain ends."
    The printed manual is available in English only. Downloadable PDF is available in English and Spanish. 
  • Engineering toolbox properties of water - http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html and email: editor.engineeringtoolbox@gmail.com web search 09/16/2010
  • Owens Corning Duct Solutions - www.owenscorning.com/ductsolutions/ - provides current HVAC ductwork and duct insulating product descriptions and a dealer locator. Owens Corning Insulating Systems, LLC, One Owens Corning Parkway, Toledo, OH 43659 1-800-GET-PINK™
  • "Flexible Duct Media Fiberglas™ Insulation, Product Data Sheet", Owens Corning - see owenscorning.com/quietzone/pdfs/QZFlexible_DataSheet.pdf
    "Owens Corning Flexible Duct Media Insulation is a lightweight, flexible, resilient thermal and acoustical insulation made of inorganic glass fibers bonded with a thermosetting resin."

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

  • Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
  • Complete List of Air Conditioning & Heat Pump Design, Inspection, Repair Books at the InspectAPedia Bookstore.
  • Home Reference Book - Carson Dunlop The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
  • Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
  • Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
  • "Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
  • Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages
  • Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
  • Air Conditioning Inspection, Diagnosis, Repair, Efficiency all the basics for home owners, inspectors, new repairmen
  • NewAir Conditioning SEER - New DOE Air Conditioner and Heat Pump Efficiency Standard
  • Asbestos HVAC Ducts and Flues field identification photos and guide
  • Fiberglass: Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation
  • ...
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