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Air Conditioning & Heat Pump Air Handler
Blower Assembly, Blower Fan, Cooling Coil / Evaporator Coil & Air Filter: inspection, diagnosis, & repair guide
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Indoor air handler or blower unit for A/C or heat pump or furnace systems: how to inspect & repair the
indoor components of air conditioners and heat pumps: the air conditioning system indoor air handler units, blower units, or AHU's, (also called fan coil units) including the air conditioner blower fan, the indoor cooling coil or "evaporator coil", 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. Air Conditioning Blower Fan, Cooling Coil, Fan Coil Unit Leaks, Mold, and Filter Problems &: Repairs.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Air Handling Unit Troubleshooting - Quick Checks
 Basic air handler unit or blower unit troubleshooting checks: Here we provide air handler unit or blower assembly troubleshooting by expanded annotated information from the US EPA [5] who provided suggestions for investigating the air handling unit during an indoor air quality investigation. Also see our complete HVAC cooling and heat pump diagnostic guide beginning at LOST COOLING CAPACITY.
- Is the system turned on? Check thermostat to see that it is calling for heat or cooling, service switches at the equipment, check fuses or circuit breakers serving the equipment; for cooling systems check for a condensate drip tray overflow switch that may have turned off the system.
- If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS. If all of the controls are calling for system operation but the blower motor won't run, see ELECTRIC MOTOR DIAGNOSTIC GUIDE.
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.
- Is air flowing from the air supply registers? see DUCT SYSTEM & DUCT DEFECTS - also check for a clogged or dirty filter or blocked air return. 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.
- Is the blower assembly fan operating? You should hear the fan motor running and the fan assembly should be spinning. If the blower fan motor won't run see BLOWER FAN OPERATION & TESTING and see ELECTRIC MOTOR DIAGNOSTIC GUIDE.
- Are the air filters installed, proper size, clean? See AIR FILTERS for HVAC SYSTEMS
- Are the duct dampers working? Some HVAC systems use manual or automatic duct dampers or ZONE DAMPER CONTROLS to open or close airflow through individual duct system sections. Commercial and large building duct systems may include fire dampers that could be closed.
- Is the air handler or its condensate drip tray dirty? Are there moisture, debris, visible mold, or other contaminants (rodents, birds) in or around the air handler or blower assembly? See DIRTY A/C BLOWERS below in this article.
- Are the coils dirty or iced or blocked? Are the evaporator coils (cooling coils or heating coils) clean? See DIRTY COOLING COIL and see FROST BUILD-UP on AIR CONDITIONER COILS
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
- Is the condensate pan clean and is condensate draining out of the pan? See CONDENSATE HANDLING, A/C
- Is the heating combustion equipment venting properly and does it have adequate combustion air supply? See CHIMNEY INSPECTION DIAGNOSIS REPAIR and BACKDRAFTING HEATING EQUIPMENT
Outdoor components: For a discussion of the outdoor components of an air conditioning or heat pump system see COMPRESSOR & CONDENSING COIL, A/C.
Dirty A/C or Heat Pump Blower Units - Dirt-blocked air conditioner air handler fans
We also 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.
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
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 Notice the multiple colors and textures of mold growing on this air conditioner squirrel cage blower fan. Mold, depending on its genera/species, moisture conditions, and growth substrate material, can grow on many different
surfaces where some organic material is available for "food".
We might find mold growing in an air conditioner on plastic, on air cabinet or duct insulation facing, hidden in fiberglass insulation, or on other materials.
Most likely the mold growing on this blower fan found a home in some of the organic constituents of common house dust: skin cells and dust mite fecals.
Very often the mold we sample and identify in air conditioner blower cabinets is a very common genera, Cladosporium sp. - a mold so common it's called "the king of molds." Kicking up leaves outdoors exposes you to more Cladosporium sp. than the mold on this
blower fan.
But we also find some genera/species of more toxic molds that will grow right on top of other molds that are already present. So while air cabinet conditions may start by producing one mold of not too much concern, other more
highly allergenic or even toxic molds could be present.
The fact that the mold in this photograph includes multiple colors and textures of material suggests that more than one genera or species of mold is present.
How to Handle Small Areas of HVAC System Mold Contamination
If the total area of moldy material
is small (say less than 30 sq.ft. of contiguous mold) we would not bother to take a mold sample back to our lab for identification. Instead we'd suggest that the moldy surfaces be cleaned or non-cleanable material like insulation, replaced, and the cause for its growth corrected.
We might, however, sample even a small amount of visible mold as part of a larger building diagnostic program if there were illness or air quality complaints associated with the building.
Examples of condensate spill-over inside of an air handler blower compartment, a condition creating a risk of mold growth inside the HVAC system are at BLOWER LEAKS, RUST & MOLD
Information about the potential of toxic mold growth in fiberglass ducts or fiberglass HVAC duct insulation as well as other fiberglass insulation products and more example photographs of that condition are at Mold in Fiberglass in Insulation. |
How to Keep 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. See AIR FILTERS for HVAC SYSTEMS.
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 HVAC blower assembly 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 in all buildings.
Frequently Asked Questions (FAQs)
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Questions & answers or comments about how to diagnose & repair problems with the air handler or blower unit / fan assembly in a warm air furnace or air conditioning system .
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Thanks to AMark 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
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
- Wikipedia provided background information about the definition of HEPA and airborne particle interception.
- [5] US EPA - Mold Remediation in Schools and Commercial Building [ copy on file as /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
- 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
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
- Air Conditioning SEER - New DOE Air Conditioner and Heat Pump Efficiency Standard
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
- COMPRESSOR CONDENSER: problems with air conditioner compressor/condenser units
- AIR HANDLER / BLOWER UNITS: 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
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, 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. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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