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AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE EFFICIENCY RATINGS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of Heating & Cooling Terms
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
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.
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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  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.
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.
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.
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.
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.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
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.