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.