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Old 01-28-2015, 10:59 AM   #1
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Help with Furnace/AC - Short Cycling?


Hello. I am having an issue with my central heat/air, and I could really use some assistance with troubleshooting it.

The issue I am having is with my inside unit, American Standard model# TWE031E13FB1. About a week ago I turned on the heat & the inside unit came on for about 5 seconds, but then it shut off for about 30 seconds, then it would start up again, then shut off again. It would cycle like this until I turned it off at the thermostat. Inside the unit I could see the element heating up, but then it would make a clicking noise & it would shut off, this was the same time as the blower/fan was shutting off. In researching, it appeared that the high limit switch needed replaced. I pulled it, tested it and it was open, so I replaced it.

This seemed to solve part of the problem, it doesn't make the audible click sound like it was before before shutting down, but the blower/fan still isn't running properly. When I turn the unit on and call for heat, the fan/blower starts spinning, but then after about 7 seconds it seems to lose power for a moment and cut off for about 7 seconds, then it starts spinning again for another 7 seconds, then it slows down for 7 seconds again. It will cycle like this until I cut the power or turn off the thermostat. I looked at the circuit board, but I did not see any melting, etc. One thing I did notice is that the CFM light on the circuit board goes dark right before the fan cuts off, then it will flash and light back up, over and over. (I have no idea what CFM stands for, or what this light represents, just thought I would mention it). It does this same thing for both Heat and A/C, and it also does the same thing whether the thermostat is switched to ON or AUTO.

Any idea what this issue could be? Any help would be greatly appreciated.

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Old 01-28-2015, 11:51 AM   #2
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Help with Furnace/AC - Short Cycling?


cfm> cubic feet per minute the fan is moving air

Try remove your thermostat from the wall and then put a jumper wire between R and G and see if the fan runs. That is what turns it on with heat and AC and if the tstat is bad then it will run properly and you need a new one. If not then there may be a problem with the circuit board.

Shut off power b4 removing the tstat. Then put the jumper on and restart w/o the tstat attached.

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Old 01-31-2015, 01:43 PM   #3
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Help with Furnace/AC - Short Cycling?


Thanks for your response. I removed the thermostat & connected a jumper wire from G to R, but then I get nothing at all from the fan. The CFM and FAN lights are lit on the control board, but no movement from the fan. Here's a photo of my thermostat wiring, just to make sure I ran the jumper correctly (black wire).
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Old 01-31-2015, 02:41 PM   #4
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Help with Furnace/AC - Short Cycling?


Do you have a ECM Variable speed motor. It usually has 2 wiring harnesses going into the motor nout just 4-5 ordinary wires. Those will rock when they start as they are charging a capacitor. You may have a problem with the built in circuit board in the motor or the motor itself. Need a special tester/simulator and a sercvice manual to troubleshoot those. Post some well lit pics of the motor. Not usually a DIY job those motors. Your jumper is OK.

May want to get a AM Std or Trane tech as that is some pretty specialised equipment and test procedures.
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Old 01-31-2015, 02:45 PM   #5
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Yep,fan should be running now. If not it could be the board, capacitor or motor.
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Old 01-31-2015, 10:17 PM   #6
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Looks like an ECM. Here's some pics.
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Old 01-31-2015, 11:34 PM   #7
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Also, when I removed the jumper & reattached the thermostat, the motor now doesn't do anything,where before it was turning on/off every 7 seconds.
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Old 02-01-2015, 07:24 AM   #8
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Help with Furnace/AC - Short Cycling?


Could be the control board, or the VS ECM module. Jumper R to Y, and see if it runs.
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Old 02-01-2015, 09:14 AM   #9
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It may have a 10 yr warranty on parts.

Hate to say it but that fan looks pretty dirty. You don't want a dirty wheel or motor or (now) AC coil as it overloads the motor and overheats it. You MUST maintain/change the filter properly and not use anyhting less than a Merv 8 grade or it lets too much dust thru. The higher than Merv 8 can overload the motor so it is a best idea to use a Merv 8.

Those motors are a constant speed/torque and as the filter plugs up they speed up but eventually they reach their top speed and start to cavitate/hunt and cannot maintain their speed properly and get damaged and die. It is serious stuff.
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Last edited by yuri; 02-01-2015 at 09:16 AM.
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Old 02-04-2015, 09:57 PM   #10
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Help with Furnace/AC - Short Cycling?


Jumping R to Y caused the outside unit to come on, still nothing from the fan. I also tried jumping at the unit itself, but still no luck.

I'm not sure if it's under warranty or not. We recently acquired this home, so it's all fairly new to us. When we first moved in we were using cheap filters, but then recently switched to more expensive ones. I was not aware of the Merv 8 recommendations. I believe the ones we've recently been using are Merv 12 or 13. I had no idea it could overload the motor.

I tested voltage at the motor & the wiring is getting 24V. I found a test on YouTube to determine if the module was the issue, but the fan did not run, so apparently it's not the module. Are there additional tests I can do to determine if the motor is in fact the issue? What if I pull the motor & separate it from the module, can I test it somehow with a multimeter?
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Old 02-04-2015, 10:06 PM   #11
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Correction. I reviewed the YouTube video again & because the fan didn't start in the test, it's more than likely the module. Is there is way to be sure the module is the issue?
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Old 02-05-2015, 03:56 AM   #12
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Help with Furnace/AC - Short Cycling?


Still could be the module, the control board, or the motor itself.

If you take the module off the motor, you can look inside the module to see if the varisiter is burnt out.
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Old 02-05-2015, 09:00 AM   #13
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Help with Furnace/AC - Short Cycling?


Usually in the service manual or sometimes the install manual there are troubleshooting steps. the service manual will have the test points and voltages etc.

Have to get that from a dealer or call one. Not everything is DIY friendly or accessible as their support sites are password protected. Every brand has its own method for checking ECM motors and their own boards.

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