I undertook what I thought would be a straight forward task.... Needless to say I have run into an issue that I need some help with.

The replacement motor is a century 4ka35 motor with the following wires. I only need the high speed setting as the air handler is older and not setup for multiple speeds even though the old motor was multispeed.

Brown and Brown/white to the capacitor, Yellow to L1, Black(hi speed) Blue (med Speed) Red (lo Speed) to L2

I have the brown wires connected to the the capacitor, the black wire connected to the rd/3 wire shown in the diagram (this wire was connected to the hi speed terminal on the old motor) and the motor does not seem to get up to speed. Do I need to connect the l1 wire to something, if so what as I can't find it on the diagram.

air handler (Model American Standard/Train TWE036C140B0) wiring diagram wiring diagram image 1 of 2 wiring diagram image 2 of 2

  • We need to see the wiring diagram off the new motor.
    – Paul Logan
    Jan 6, 2018 at 19:43

1 Answer 1


That is a horrible wiring diagram but basically the the black wires on the air handler are L1 and the red are L2 (or vise versa ). The yellow wire from the motor would connect to the black (L1) air handler wire and the black (hi) wire from the motor would connect to the red wire (L2) from the air handler. The two brown wires from the motor go to the capacitor and the remaining speed tap wires (blue and red) get caped individually. You should check that the new motor is indeed 230 volts. Some are dual voltage and need to be set up for 230v. Also make sure that the microfarad rating on the capacitor and the motor match.

  • This did the trick. Thank you very much. The new motor was a 230v motor and I did get a new capacitor that matches the motor. Though I solved this problem I am now having an issue with the same system where the blower fan comes on, and nothing else works (outside unit, heat strips etc) and won't shut off unless I trip the breaker. I have even tried replacing the t stat and ended up with the same problem.
    – user79982
    Jan 7, 2018 at 20:46
  • That is most likely the circuit board since I do not see any limit switches in the wiring diagram. Check to make sure that RD/3 wire is going directly from the motor speed tap, in your case the black motor wire to the FDR (fan delay relay terminal 3. That relay is what is determining whether or not the motor is getting power. The circuit board determines whether or not the relay is open or closed. If the relay is closed the fan should be on.
    – user76730
    Jan 7, 2018 at 22:51
  • Disconnect all the thermostat wires from the air handler to make sure the problem is not in the thermostat wires or thermostat. If the fan stays on it is in the air handler. If it goes off jump the R and G wires, the fan should come on. As far as turning on the heat pump, that is all controlled at the outdoor unit coming directly from the thermostat (there may be an orange and yellow wire that goes from the thermostat up to the air handler and down to the heat pump but is not actually connected to the air handler electrically, just a convenient place to make a splice.
    – user76730
    Jan 7, 2018 at 22:59
  • Hi. Once again thank you. I ended up following your troubleshooting tips and unplugged the harness for the t stat from the air handler and the fan kept running so I replaced the fdr board and the fan works as it should. I still have the issue where it is just blowing cold air the heat strips don't come on and it does not seem to go into heating mode. the outside unit does come on now. I did put a thermometer up to the duct and it was blow 60 degree air. Any additional ideas?
    – user79982
    Jan 12, 2018 at 2:04
  • @user79982 since this "did the trick", please give the answer a check-mark so others will know that this is a good answer that solved the problem
    – FreeMan
    Aug 11, 2020 at 21:23

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