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. 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. 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 installationsHow Much Does It Cost To Put Tire On Rim and high-rise apartment buildings. Woodland 8-Piece Reversible Comforter Set QueenThe unit shown has its own compressor mounted right in the cabinet, visible at lower center inPuffy Ink T Shirt 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.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 (above 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. Details about wall convectors used for heating or cooling and about convector blower fans are found at WALL CONVECTORS HVAC and at FAN CONVECTOR HEATERS - HYDRONIC COILS Also see CONDENSATE HANDLING, A/C for more about air conditioner or heat pump condensate drainage handling. In our simple air conditioning (or heat pump) system sketch shown at left, the light blue fan shown at left in the sketch (above the red compressor box) is the outdoor compressor/condenser fan discussed

at FAN, COMPRESSOR / CONDENSER UNIT. The dark blue fan shown at right in the sketch is the indoor air handler or blower compartment or cooling coil fan found inside the building. This fan blows building air across the evaporator coil (or cooling coil) to cool and dehumidify indoor building air. We discuss this indoor fan at FAN, AIR HANDLER BLOWER UNIT. In a warm air heating system that does not include air conditioning as well, the indoor fan is still located in the indoor air handler and is discussed Question: What do I do about a squeaking, squalling squirrel cage? It doesn't do it every time the A/C comes on but more frequently than not. Not alot of room to see in there. The squirrel cage fan to which Erma refers is found inside the indoor air handler unit. This fan moves building air through the duct system and across heating and/or cooling elements to condition the air as it is then supplied to the building through supply ducts and registers. In an air conditioning system this is the dark blue fan shown in the right side of our sketch above.

For combined heating/cooling systems the same fan assembly can blow heated air into the building and an additional FAN LIMIT SWITCH will be found inside the furnace cabinet. More about HVAC blower fans including squirrel cage fans is in this article, above beginning at BLOWER FAN OPERATION & TESTING but to start addressing a squeaky blower fan, note that your fan may be repairable by tightening one or more allen screws that secure the fan cage assembly (or the bearings that carry the fan) to its housing through which passes the fan motor drive shaft. With power OFF for safety, if the fan and all components appear to have no loose screws or mounts, but you can still wiggle the fan from side to side, then the bearings are worn and need replacement. If your fan is pulley-driven, check also that the pulley is secure on the shaft and that the fan belt is not so loose as to be squeaking. I would not use WD40 on or near electric motor parts nor on greased bearings as it's not intended for a motor or bearing lubricant, though to be honest, I've sprayed WD40 on almost every problem that has ever arisen at one time or another.