After getting my furnace blower motor replaced, it now runs only in the following scenarios:

  1. Mode "Cool" Fan "Auto"
  2. Mode "Cool" Fan "On"
  3. Mode "Heat" Fan "On"

In other words it will not run when in "Heat" mode with Fan "Auto". I believe it could have something to do with the way the motor is wired.

Please see the images and link below for information on how it is currently wired. Any advice would be greatly appreciated as we are moving into winter quickly here!

Click here for Furnace and Blower Motor Information

Wires Coming from Original Furnace enter image description here

Wires Coming from new Blower Motor enter image description here

How the wires are connected currently enter image description here

  • 2
    Both motors should have wiring diagrams printed on them. Just match them up. Follow the wires from those splices, back to the control board, or check the schematic. That will tell you how to wire everything.
    – Tester101
    Commented Nov 1, 2015 at 3:37
  • According to the new motor White = L1 (neutral), Black = High speed, Blue = Medium speed, Red = Low speed. Check the diagram on the old motor, to figure out which wires are which. From what I can see, looks like on the old motor: Black = High speed, Yellow = Medium high, Orange = Medium Low, Red = Low speed.
    – Tester101
    Commented Nov 1, 2015 at 3:43
  • Yes, and that is what i had done. The problem is there is an extra setting (orange wire) on the old motor that isn't there on the new one (medium low). Commented Nov 1, 2015 at 3:50
  • 1
    Probably not all the speeds were used, you'll have to check where they connect to the control board. Most likely, one or two go to a PARK terminal, which means they're not used. Heat mode probably should use low, or medium low speed.
    – Tester101
    Commented Nov 1, 2015 at 3:55
  • 4
    When the heat is on, wait for the delay 30-90 seconds, depending on the jumpers). Then check for line voltage between the white, and the orange wires. Then check between white and yellow. If you have voltage on one of them, connect the blue wire to it. If you don't have voltage on either, the problem is with the fan control circuitry (probably a fuse, relay, limit, or something else on the control board).
    – Tester101
    Commented Nov 1, 2015 at 4:20

3 Answers 3


Check the resistance from the White wire (neutral) to each wire. The higher the resistance, the lower the motor speed.

Example :

  • White to Black: Check resistance, write it down.
  • White to Red, White to Blue, etc.
  • The higher the resistance, the slower the speed.

Black is "generally" HIGH speed. Red Is "generally" the lowest speed. This is NOT always the case. ALWAYS check resistance to verify the proper wiring speed.

  • Brown wires (Brown & Brown with White stripe): Usually go to capacitor on 120 Volt motors

Cooling mode "generally" calls for the highest speed. Heating mode "generally" calls for Medium to Medium High. Depends on the furnace AND the manufacturer specs for Heat Temp Rrise.

Always check Temp rise on all blower replacement.

Hope this helps..

  • 1
    Hello, and welcome to Stack Exchange. You've answered a bunch of questions in the last few hours: many thanks. However, it would be great if you could put a bit of time into formatting your answer; that would let visitors better understand the great info you're bringing here. (Keep 'em coming!) Commented Nov 3, 2018 at 16:52

I just finished replacing the GE motor in my unit with a Mars blower motor. I had the same issue, one extra wire. But there’s a chance the orange wire is actually the common wire and the yellow is one of the two med settings (med hi or med lo). That turned out to be the case in my unit. On my new motor, I had black, red, blue, and yellow. On the old one, it had the extra orange as well. So here is how mine is wired and works correctly: New motor. Unit Side Black-hi. Black-hi Blue-med. Blue-med Red-lo. Red-lo Yellow-common. Orange-common

So that’s black to black, blue to blue, red to red, yellow to orange. The yellow wire on the unit side is dead ended (goes nowhere but has a wire nut to prevent any possible short).

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here. Commented Aug 14, 2019 at 20:22
  • perhaps your furnace needs the speed that is disabled. if it senses that, it will not go into heat mode. for example, this could happen if a 3-speed motor is used to replace a 4-speed motor, and the installer choose which speed to disable.
    – doc freeze
    Commented Jun 11, 2021 at 2:09

Also, make sure your fan limit switch on your furnace is working (turn on thermostat to high and fan to auto and listen for furnace to start heating and watch the dial in your fan limit switch to start moving- blower should start at the first, lowest temp setting).

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