Page 220

NORA Oilheat Technicians Manual

are mounted tight to the burner housing before measuring the center piece. If you cut the center piece too long, when the motor and the pump are bolted in place, the pressure may put an undue strain on the motor and may keep it from starting. Warm air furnace motors and fans/blowers The third most common use of motors in our industry is for moving air through warm air and air conditioning ducts. Many are multi-speed motors that can be operated at any of two or more speeds. In the case of multi-speed PSC motors, the speed is dependent on the load. Three types of blower motors can be found on warm air systems: 1. The split phase, fractional horsepower motor used for belt driven blowers. 2. The capacitor start motor, also used for belt drive. 3. The multi-speed, direct drive motor/ blower assembly. These blowers are often used on systems that also provide air conditioning. They can run at a slower speed for heating and faster speed for the air conditioning. These motors can be either PSC type motors or a newer design called an ECM, see Figure 10-18. Chapter 10 Motors 10-14 Motors The ECM is a DC voltage motor. ECM stands for Electrically Commutated Motor. ECMs have grown in popularity due to their low power consumption, infinite motor speed capability and reliability. The ECM has all the efficiency and speed control advantages of a DC motor with none of the disadvantages, such as carbon brush wear, short life, and noise. The ECM uses 1-phase AC input power and converts it into 3-phase operation. Three-phase motors offer superior efficiency and reduced noise. Belt driven blowers These are the most common type blowers on older oil-fired furnaces. These motors are mounted to the blower and drive it through pulleys and a “V” belt. Adjusting the size of the pulleys changes the speed of the blower. The larger the pulley on the motor, the faster the fan will turn. The larger the pulley on the fan, the slower the fan will turn. Variable pitch pulleys can be adjusted to increase or decrease size to change the speed without changing the pulley. When adjusting the speed of this type of motor, it is imperative to take an amp reading to be sure that the increase in speed does not work the motor beyond its rated capacity. Figure 10-19 shows some of the wide variety of pulleys available. Note how the adjustable pulley opens and closes to vary Figure 10-19 diameter. Make sure it is not too far open or closed causing poor seating of the V belt. Figure 10-20 stresses the importance of using the right size belt for the pulley being used. Width of belts and pulleys varies so be sure both are the same when changing motor and pulley. Proper tension on belts without over-tightening is important. Figure 10-18: ECM motor Standard Pulley V-Step Pulley Adjustable V-Pulley Closed Open


NORA Oilheat Technicians Manual
To see the actual publication please follow the link above