Blowers,
Motors
and
Belts
This power point presentation will review
Section C2 in the Student Handout Packet.
You may also need to refer back to the basic
Electric Wiring course information on
motors.
Blower Motors: Belt Drive
1. Motor and blower are two separate devices
connected with a belt(s) and pulleys.
2. Most likely 1725 or 1750 RPM
3. 1/3 HP or less HP
4. Split Phase or Capacitor Start Motor
5. Generally an open drive housing using a
Centrifugal Switch
Blower Motors: Direct Drive
1. Blower wheel is mounted on the motor shaft.
2. Motor is mounted on blower housing.
3. Shaded Pole, PSC or ECM motor
4. These motors are multispeed
5. Lower HP for shaded pole motor
6. Higher HP for the PSC and ECM
The C2 section material does NOT deal with the
ECM motor. The ECM is covered as separate
material.
Blower Speed Adjustment
The blower speed can be changed either by
changing the wire ‘taps’ on the direct drive system,
or by changing the size of the drive (motor) pulley
on the belt drive system.
Blower Speed Adjustment
Why do we need to adjust the blower speed?
Heating requires one speed and cooling requires a
different speed.
Blower Speed Adjustment
The heating speed is determined by the
temperature rise. The cooling speed is determined
by the temperature drop. The speed of the ECM
motor is determined electronically by the
manufacturer of the heating equipment. Reference
the ECM material.
Temperature Rise
The temperature rise procedure is found in your
textbook as well as page C2c. Be sure to review it.
Pay particular attention to what you do if the rise is
too high or too low.
Temperature Rise
Formula:
Temperature Rise = Supply Air – Return Air
Temperature Rise
If the rise is too high or too low, the solution is
rather simple. If the rise is too high, RAISE the
blower speed. If the rise is too low, LOWER the
blower speed. In simple words, do to the blower
speed what the rise is. Rise high, speed up
blower. Rise low, slow down blower.
Temperature Drop
Formula:
Temperature Drop = Return Air – Supply Air
Remember this formula for this course, but more
information will be provided during the air
conditioning course, since temperature drop is for
air conditioning.
Blower Speed
The blower speed can be changed in one of three
ways.
1.Wire taps on the motor – direct drive blowers
2.Adjust pulley on the motor – belt drive blowers
3.Follow manufacturer’s directions for the ECM
motor/blower arrangement.
Pulleys
The pulley on a motor may either be of a fixed or
adjustable design. Another name for a pulley is
sheave.
Pulleys
When an adjustable sheave is open, the belt will
ride LOW in the pulley and the blower speed will
be slower. When an adjustable sheave is closed,
the belt will ride HIGH in the pulley and the blower
speed will be faster.
Pulleys
The sheave should never be adjusted open so far
that the bottom of the ‘V’ groove in the belt is off
the slope of the groove. Nor should the sheave be
adjusted closed so far that the top of the belt is
above the top of the pulley. In either situation, the
belt will not be in proper contact and will result in
improper belt wear, slippage of the belt and
improper pulley groove wear.
Belts
Belts are sized in two ways:
1.Manufacturer and part number as identified on
the belt.
2.Width at the TOP of the belt and its length
(circumference).
Belt Tension
Page C2e indicates the belt should deflect ¼” per
foot of belt span with 2 – 3 pounds of force. This is
great when you have a belt tensioning tool.
Unfortunately, most technicians do not have this
tool. Most go by ‘experience.’
Belt Tension
What does ‘experience’ teach you? The belt
deflection should be about ¼” per foot of free span
with a slight amount of tension. Remember the 2 –
3 pounds of force? This is what is described as a
‘slight amount of force.’
Belt Tension
If the belt tension is too tight it will lead to premature
failure of the belt. There will be a greater amount of
friction and this will produce heat. The heat will go
from the pulley to the motor and fan bearings and
shorten their life. If the belt is too loose, friction will
be less and there will be a power loss and the fan
may not operate at correct speed.
Lab. Time
There are several lab. assignments that relate to
blowers, motor and belts. It would be important for
you to complete the following as soon as you can.
In fact, you may need to review the information
even after you have completed it one time.
Lab. Time
1. Watch the video: ‘Belt Drive Tips’
2. Power Point Presentation: ‘ECM-CCAC’
3. Video: the ECM ‘GE Blower Box’
The three items listed above are critical to you
moving forward in the lab. relative to blowers,
motors and belts.
Additional Tip
It is highly recommended that you return to the
material from the Basic Electric Wiring course and
review information on motors and capacitors. As
part of that process, it would be wise for you to
review the Motors and Relays exam from that
course.
This concludes this review of
blowers, motors and belts.