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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 DIAGNOSIS & REPAIR
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
HVAC blower fan testing & diagnosis guide: this article discusses how to inspect and test a heating or air conditioning indoor air handler blower fan that is not working. We also discuss convector unit fans and we suggest diagnostic steps for squirrel cage blower fan squeaks and noises.
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How do I fix my indoor air conditioning or furnace blower fan: the air conditioning (or heat pump or furnace) blower fan just won't run
Our page top photo shows an air handler unit located in a building's attic - we removed the cover to show the blower fan assembly just to the left of the red tag) in this image of a Lennox™ horizontal HVAC system.
The blower fan is located inside a horizontal air conditioning unit in many home air conditioning systems, especially when the air handler is located in an attic or crawl area. The location of a blower fan in vertical "up flow" or "down flow" heating and cooling systems is illustrated in additional sketches and photographs below.
Initial, simple diagnostic checks of the air handler system are also described at DUCT SYSTEM & DUCT DEFECTS: Basic checks of the indoor air handler (blower), air ducts, and filter systems.
My issue is about an air conditioner fan that just won't start. The fan motor is not seized, and we had a recent blower motor starting capacitor change. The blower fan relay appears to pull in okay, the electrical connections reseated and tight.
But the cooling fan will still not start. This is an early 1990's York home air conditioning unit. - R.S.
Our photo (left), shows a modern blower assembly inside of an air handler. In this case the blower is a direct-drive unit - the electric motor that drives the air conditioner blower fan is mounted inside of and at the center of the blower assembly itself.
Other HVAC blower units may mount the motor separately from the squirrel cage fan, connecting the motor to the fan using a set of pulleys and a fan belt.
For completeness we have listed some blower fan diagnostic steps that you have already tried, as well as additional things to check. The blower assembly is the green component in this illustration from Carson Dunlop Associates The Illustrated Home.
Thanks to reader Randy Shaffer for suggesting this topic.
Wall convectors are often used for both heating and cooling in commercial installations
and high-rise apartment buildings. The unit shown has its own compressor mounted right in the cabinet, visible at lower center in
Wall-mounted heating and cooling convector installations may be designed with one central heater or cooling system which feeds multiple units with chilled or heated water or possibly refrigerant from a single remote heating and cooling heat pump.
Our photo (left) illustrates dual squirrel cage blower fans typically found in the bottom of a fan/convector heating or cooling unit such as this one found in a New York City apartment.
If the convector fan motors run and the squirrel cage fans spin but not enough air is coming out of your convector unit, turn off power and take a closer look at the fan blades themselves - you may need a flashlight and a mirror to make this check without disassembling the unit further than shown here (we removed the convector unit cover).
Watch out: Dirt on the squirrel cage blower fan blades can significantly reduce airflow through the unit. We have seen a 40 to 50% improvement in air flow simply by cleaning this blower fan assembly, yet it's something people rarely check.
Why? Because even a small amount of dirt in the cupped fan blade edges reduces airflow significantly, but it's not visually obvious.
You have to look carefully at the fan assembly. In our wall convector unit above you'd use a good flashlight and a mirror to inspect the blower assembly fan blades.
Also check the cooling or heating coil fins for blockage by dust and debris - a more common source of air flow blockage at heating and cooling convector units like the one shown.
Our photo (left) illustrates a condensate handling problem in the cooling convector unit for the same apartment unit introduced above.
Air conditioning condensate was leaking inside of the convector unit due to a clogged condensate drain line.
The condensate leak exited the bottom of the convector, ran through a raised floor cavity, entered apartment building walls, and ran around the wall interiors in a metal stud-framed wall sill plate where it led to major toxic mold contamination over a wide area, floor damage, and the need for costly cleanup and repair work.
Also see CONDENSATE HANDLING, A/C for more about air conditioner or heat pump condensate drainage handling.
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Frequently Asked Questions (FAQs)
Where is the "Blower Fan" or Air Handler blower located?