Aren’t all fans just fans? Nope, and understanding the differences will help solve some strange problems that your customers may have asked you about.
There are many types of fans, and talking about each type and the reasons for their unique design and purposes would go on for pages and pages. But what I’m going to discuss here are the two basic types your company encounters on a regular basis - propeller types and blowers (squirrel cages).
Propeller-style fans are designed to be used in spaces where there is little forward resistance, as in open ventilation or to move air across condenser coils. Condenser fans typically operate (on high speed) at about 3200 rpm. On better models of air conditioners, they may also be 2-speed or variable speed, to maintain a constant refrigerant pressure at varying outdoor temperatures.
The reason why propeller-type fans are used in low-pressure situations is that they draw more wattage as pressures rise. And a common reason for condenser fan motor failures is clogged condenser coils. I’ve seen condenser coils that looked sparkling clean on the outside burn out multiple fan motors because their fins were internally clogged.
Propeller fans must operate in the proper direction to blow enough air, and the blades must be properly centered inside a venturi (a curved metal housing) to move the greatest amount of air - which is often considered unimportant by technicians.
Since condenser fans usually have little starting resistance, the motors are typically psc-types (single small capacitor) on single-phase supply systems, and they must be protected so as to keep them internally dry during a rain.
Blowers (evaporator fans) are designed to be used in higher-pressure situations, as where ductwork is involved, because the higher the static pressure, the LESS wattage they draw. So air restrictions, such as dirty filters, seldom cause blower-motor failures.
Blowers usually operate at slower speeds than condenser fans (typically 1600-rpm max), and something unusual about their operation is that they blow when operating in either direction. However, when running backward, they blow poorly, and this often confuses service technicians. The blades must be rotating in the direction of the up discharge to work properly.
Motors that operate belt-drive blowers are typically capacitor start (large capacitor) or three-phase types, because of higher starting torque. Direct drives are typically psc-types with multiple speed taps (on less-expensive models), or permanent magnet types, which are operated with varying DC power (on high-end systems).
Which fan motors do I suggest that you stock? Although they cost more, I strongly advocate the use of totally enclosed motors that can be set to reverse their operation. For nothing is more frustrating to a service technician than to arrive at a job where there’s a motor failure late in the day, and find out that the last motor on your truck runs backward or will be damaged in the next rainfall.