The Air Conditioning Air Handler: Blower Fan, Cooling Coil, Filter InspectAPedia®  -     Air conditioning air handlers - Fan Coil Unit Inspection, Diagnosis, Repair, Replacement Dirty, contaminated air conditioner blower fans, reduced air output, fan cleaning advice Air Conditioning air handler unit (AHU) leaks and toxic black mold contamination Dirty or blocked air conditioner cooling coils (evaporator coils) Frost build-up on evaporator coils and its affect on cool air flow and mold Problems when adding retrofit air conditioning to a warm air heating system

This article discusses the air conditioning system air handler units, blower units, or AHU's, (also called fan coil units) including the air conditioner blower fan, air conditioning system filters, and the causes, cures, and prevention of air handler leaks that lead to rust, damage, and mold contamination in the air conditioning system. We discuss how to improve indoor air quality by installing a cascaded air filter system at the air conditioning (or heating system) air handler to provide optimal air particle filtration for people with asthma, allergies, or indoor mold or other IAQ concerns.

Also see COOLING COIL or EVAPORATOR COIL for a description of diagnosis and repair of cooling coil problems since this component is normally located within the air handler chassis as well. A cooling coil which is blocked by debris or ice and frost can obstruct air flow and reduce air conditioning system output.

If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS. See How to determine the cooling capacity of air conditioning equipment if the system seems to be working but is inadequate to cool your building. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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Initial, simple diagnostic checks of the air handler system are also described at Ducts & Air Handler diagnosis: Basic checks of the indoor air handler (blower), air ducts, and filter systems.

DIRTY A/C BLOWERS - Dirt-blocked air conditioner air handler fans

Filters protect the blower assembly: The typical A/C system circulates air through the building duct work using a "squirrel cage" blower fan. It is very important for you to check and change air filters at least monthly when the system is in use to protect the blower fan from dirt clogging.

Cupped fan blades can become blocked by debris: The blades of a squirrel-cage fan are cupped in order to cause the spinning cage to move air.

Dirt accumulation on the blades fills-in this cupped area, ultimately changing the "cup" to a simple flat area. The fan will spin just fine. I've seen the cubic feet per minute of air conditioning air-flow literally double when a very dirty squirrel cage fan fan of this type was cleaned or replaced.

Cleaning an air conditioner squirrel cage fan with compressed air? If the blower fan blades have significant dirt accumulation, you should have the system professionally cleaned. While this is a fairly costly service call (requiring blower disassembly and removal for cleaning) it can make a dramatic improvement in system performance.

Do not permit a simple "blow out" of the blower by compressed air if the air handler/blower are in the living area. Some HVAC service companies use a foaming cleaner for removing debris from an evaporator coil. That same material might assist in cleaning a squirrel cage fan.

Otherwise we recommend removing the fan and cleaning it thoroughly outside. Clean the remainder of the fan cabinet and housing before returning the air handler to service.

Leaks, Dirt, Rodents Getting Into HVAC Blowers, Blower Compartments, Air Plenums

Very dirty, wet, leaked-into, or rodent-infested blower compartments risk indoor air quality and health issues in buildings. The air handler unit in the photo at left needs cleaning and a check for unsafe wiring due to leaks. Leaks into the blower compartment of an HVAC air handler invite mold problems too.

The return air plenum in the photo at right has both a dead mouse and some other sort of trash that probably fell down a return air floor grille. Mice in HVAC systems are a potential viral or bacterial hazard as well as an indicator of poor housekeeping. These conditions suggested that there had not been regular inspections of this equipment.

Causes & Photographs of Mold Growth in Air Conditioning Blower Fans

Basic Tips on Keeping the HVAC Blower Assembly Clean

BLOWER OPERATION: For effective operation of this system it is essential that it never be operated without air filters in place. If you permit the filters to become very dirty you may need expensive special cleaning or other repairs. See BLOWER FAN OPERATION & TESTING.

COOLING MAINTENANCE TIP: The system should be serviced every two years. Without proper service the system may have no more than a five year lifetime. ENERGY CONSERVATION: Keeping the fireplace flue closed (if you have one) when not in use will improve both heating and cooling efficiency.

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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
A/C - HEAT PUMP CONTROLS & SWITCHES
A/C DATA TAGS
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
  Missing or Leaky Air Filters
 OPTIMUM INDOOR AIR FILTERS
 CONTINUOUS BLOWER FAN OPERATION
 AIR FILTER EFFECTIVENESS
 FIBERGLASS & AIR FILTERS
 SOURCES FOR AIR FILTERS
  OTHER AIR CLEANERS
AIR HANDLER UNITS
  ADDING A/C: RETROFIT SIZING
  BLOWER FAN OPERATION & TESTING
  BLOWER LEAKS, RUST & MOLD
  COOLING COIL DEFECTS
  DIRTY A/C BLOWERS
    Leaks, Rodents In Air Handlers
    Mold Growth in Air Handlers
BACKUP HEAT for HEAT PUMPS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
COMPLETE COMBUSTION, Stoichiometric
CONDENSATION or SWEATING PIPES, TANKS
COMPRESSOR & CONDENSING COIL
CONDENSATE HANDLING
  DRIP TRAY DEFECTS
    Missing Condensate Overflow Pan
    Improper Condensate Drain Connects
    Float Switch on Condensate Tray
    Water in Condensate Overflow Pan
  CONDENSATE LEAKS
  CONDENSATE PUMPS
  CONDENSATE DRAINS
    Locations for Condensate Disposal
    Plumbing Code for Condensate Drains
    Improper Condensate Disposal
    Condensate Drains Connected to Vent Pipe
    Condensate Spills in Crawl Spaces
    Condensate Leaks Onto Heat Exchangers
    Condensate Disposal Outdoors
    Condensate Drains to Hidden Location
  CONDENSATE DRAIN CLEAN & DE-CLOG
  CONDENSATE TRAY CLEANING
A/C - HEAT PUMP CONTROLS & SWITCHES
COOL OFF HEAT Thermostat Switch
COOLING CAPACITY, RATED
COOLING COIL or EVAPORATOR COIL
  DAMAGED COOLING COIL
  DIRTY COOLING COIL
  DIRTY COIL CLEANING PROCEDURES
  FROST BUILD-UP
DATA TAGS on AIR CONDITIONERS
DEFINITION of Heating & Cooling Terms
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DUCT SYSTEM & DUCT DEFECTS
DUCTS - Asbestos
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCTS, Asbestos Transite Pipe
DUST FROM HVAC?
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ENERGY SAVINGS in BUILDINGS
EVAPORATIVE COOLING SYSTEMS
FAN AUTO ON Thermostat Switch
FAN CONVECTOR HEATERS - HYDRONIC COILS
HEAT LOSS (or GAIN) in BUILDINGS
HEAT PUMPS
HUMIDITY LEVEL TARGET
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS
LEED GREEN BUILDING CERTIFICATION
LEED Building Designation & IAQ
LOST COOLING CAPACITY
MANUALS & PARTS GUIDES - HVAC
MOTOR OVERLOAD RESET SWITCH
OPERATING COST
OPERATING DEFECTS
OPERATING TEMPERATURES
REPAIR GUIDE for AIR CONDITIONERS
REPAIR & DIAGNOSTIC FAQs for A/C
REFRIGERANTS
REFRIGERANT PIPING & DISTANCES
SEER RATINGS & OTHER DEFINITIONS
SYSTEM OPERATION
SWAMP COOLERS
THERMOSTATS
THERMOSTATIC EXPANSION VALVES
CRITICAL DEFECTS
Air Conditioning "How To" Books

• 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.
• 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.).
• Wikipedia provided background information about the definition of HEPA and airborne particle interception.

How to diagnose and fix an air conditioning system that is not working

Since the failure of an air conditioner to turn on, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioner or air conditioning system, after reviewing the lost air conditioner cooling diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below. To return to our air conditioning and refrigeration home page go to AIR CONDITIONING & HEAT PUMP SYSTEMS.

If your air conditioning or heat pump system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.

• A/C - HEAT PUMP CONTROLS & SWITCHES: air conditioner controls and switches - begin here if your A/C won't start. Here's an important tip: most refrigeration problems, in air conditioners, refrigerators, or freezers, are electrical, not mechanical. In air conditioning school, we used to drive out and collect abandoned refrigerators that people were tossing out during our community's spring cleanup week. Taking these appliances back into the shop we found that almost always the problem that had caused the owner to dispose of their air conditioner or freezer was in an electrical connection or electrical control. So it's worth checking out switches and controls on an air conditioner before replacing more costly components.
• OPERATING DEFECTS: major air conditioning problem symptoms and how to get the air conditioning system working again,e.g. compressor or fan noises, failure to start, and inadequate cool air volume
• LOST COOLING CAPACITY: what to do when not enough cool air comes out of the system
  • What to check first if there is no cool air or not enough cool air
  • Compressor failure diagnosis: basic checks of the air conditioner compressor
  • Ducts & Air Handler diagnosis: basic checks of the indoor air handler (blower), air ducts, and filter systems
• COMPRESSOR CONDENSER: problems with air conditioner compressor/condenser units
• AIR HANDLER UNIT: problems with the air handler, air filters, and the cooling coil itself
• DUCT SYSTEM DEFECTS: problems with the air duct system, air filters, supply registers, return air registers
• A/C REFRIGERANT LEAK DETECTION: how to use a TIF5000 to detect air conditioning refrigerant gas leak
• A/C DIAGNOSTIC FAQs: air conditioning system diagnostic FAQs: Q&A about air conditioner repair - a detailed air conditioning system diagnostic checklist

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.

• 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
• Air 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
• ...