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How do I choose the proper motor for my air conditioner, heat pump, or furnace.
Troubleshooting Guides

Choosing a replacement motor for your heating or cooling system is easier than you think.  HVAC technicians use their experience every day to choose the proper motor for replacement using the following technique.  This technique is usually followed to use a universal style motor than it is using an exact manufacturer replacment.  The advantages of using a univeral style replacement is the cost.  Older systems manufacturer motors can be obsoleted and the process for choosing a replacement is the same. 

Step 1
Is the unit a gas furnace or heat pump? 
Remember a heat pump has a 2 parts - the outside heat pump and the inside air handler.


Step 2
Choose a category from below.

Gas furnaces - Blower motor 115 Volt
Air Handler - Blower motor 230 Volt
Heat Pump - Condenser Motor 230 Volt
AIr Conitioner - Conderser Motor 230 Volt

Step 3
What is the Hp or horse power rating? - Look on the existing motor for the information. 
Some universal motor have a range of horse powers.  As long as the hp is within the range is perfectly acceptable to use.

Step 4
What is the speed? -Look on the existing motor for the information.
A multspeed motor will only have the highest RPM rating labeled onit.
It is common for motors in furnaces to have 1 to 4 speeds with each of the lower speeds running a lower RPM.

Step 5
Frame Size - Look on the existing motor for the information.
The frame size is the motor physical dimensions and every motor has an assigned frame size. ( do not worry about a letter after the 2 digit frame size such as 48Y)

Most residential HVAC systems use the following frame sizes

42 - Used mostly on ac and heat pump condenser fan motors
48 - This is the most commonly used frame size for blower and condenser motors
56 - not so common

Step 6
What is the shaft size? Most widely used is 1/2" diameter.

Step 7
How many speeds does my motor have?  Look at the electrical schematic on the motor to find out.
These are the most commonly used. 
High Speed
Medium High
Medium Low

If the schematic is missing or unreadable, then count the wires going to the motor. 
5 wires = 4 speed
4 wires = 3 speed
3 wires = 2 speed
2 wires = 1 speed

Step 8
What direction does the motor turn?  CCW or CW (counter clockwise or clock wise)
This can be confusing if you do not know from what end of the motor to look.  Face the shaft away from you and rotate the fan in the proper direction.   If is is CCW, then the direction is CCWLE and CWLE for clockwise direction.  Universal style motors have an option to reverse the direction of rotaion so rotation is not a worry.

Step 9
How is the current motor mounted?
1.   Belly Band  - The motor has what is known as a belly band around it with mounts that screw or bolt to the blower fan housing.
2.  Mounts of Ear mounts - are a permanenet part of the motor that screw or bolt to the blower fan housing.
3. Independent Mounts - The mounts attached to the side of the motor and then screw or bolt to the blower fan housing - very common for Rudd and Rheem models
4.  Flex Mount - the motor has a frame that mounts around the entire motor - very common for Trane and American Standard models.
5.  Stud Mounts - The motor is mounted using threaded studs that are part of the motor - most condenser fan motors are mounted this way.

You can replace the belly band, ear mounts, and flex mounts with the a universal belly band mounting kit.

You now have enough information to choose a replacement.

*This guide's intention is to provide an understanding of the operation of a furnace.  It is not intended as a hands-on teaching tool, or aide.  All HVAC equipment should be serviced by a licensed HVAC technician. Consult your local, town, city, and state laws, oridinances, and regulations prior to accessing, engaging, troubleshooting, repairing, or servicing any HVAC equipment. 

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