Ambient Sensor/Thermistor failed after broken fan blade jammed fan motor?


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Old 03-26-17, 10:23 AM
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Ambient Sensor/Thermistor failed after broken fan blade jammed fan motor?

I have a window AC,Fridgidaire Electrolux LRA074AT726,which reports Error Code "AS" , meaning the Ambient Sensor/Thermistor has failed.This happened after the fan blade had broken [& was jammed] so the fan motor could not turn & the AC was running for 2-3 min. I replaced the fan blade.

My Question: Could the the thermistor have failed/burned out/overheated because of the strain on the jammed fan motor?

Is this a Thermistor of the type that is used for safety: to prevent overheating/overcurent? [I realize it's also an Ambient [air temperature] Sensor.]

Will I be able to tell if the thermistor is burned out [or open circuit] when I pull it out to replace it?

Would a failed thermistor allow cold air to be produced?
 
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Old 03-26-17, 10:31 AM
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That thermistor should be the one in front of the coil which means the broken fan should have had no effect on it.

There should be two of them.
An evaporator sensor which is mounted very close or touching the coil.
An ambient sensor which should be away from the coil to sense room ambient temperature.

Have you tried unplugging the unit for five minutes or so ? That may reset the electronics.
 
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Old 03-26-17, 05:43 PM
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That thermistor is the one in front of the coil! I don't think I disturbed it [it looks unharmed], nor the wire that leads to the control panel, [& the control panel is protected by a metal cover/housing].

I did take the case apart & moved the rear coils to get the new fan in. Could that be the cause of the "AS" error message? I am now unable to enter any temperature settings because of the "AS" error message in the temperature window.
 
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Old 03-26-17, 06:02 PM
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The wiring diagram of the circuit board shows two thermistors connected but not exactly where they are located. If you had an ohmmeter you could them at the control board. They should be very close in resistance.

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Old 03-27-17, 10:57 AM
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Thanks,Pete!
I have the control board open. Everything looks fine : no damage at the board or to wires or thermistor.

The Ambient Sensor/Thermistor has a tiny white plug connection that can be detached for replacement,but I'd prefer not to fiddle with it for now.
Can I use the ohmmeter to test the 2 contacts on the back of the board?
If the Ambient Sensor/Thermistor is failed should I expect infinite resistance = open circuit?

The capacitor is very near, but easy to avoid--is it a danger when testing?

How often do these Ambient Sensor/Thermistors fail?
 
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Old 03-27-17, 11:11 AM
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Thermistors rarely fail. Yes, stay away from the cap.
 
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Old 03-27-17, 11:14 AM
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If it's on the board.... it's a low voltage capacitor. If not, you can discharge it by shorting it out with a screwdriver. They don't stay charged long.

The thermistors rarely go bad. The wiring can be thin and frail though.
The thermistor should measure around 10k (10,000) ohms.
If it measures open....it's bad.
 
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Old 03-27-17, 12:13 PM
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Measuring the ambient sensor/thermistor, disconnected from the control board, I get 12.6 on the 20K Ohm scale & on the 200K Ohm scale.

On the terminals leaving the small white connector plug,that lead to the control board, with the sensor disconnected, I also get about I get 12.6 on the 20K Ohm scale & on the 200K Ohm scale,which I don't understand!

But on the back of the control board I get infinite resistance on all scales [it says 1] with the sensor connected or disconnected.
 

Last edited by Roark Hunnicutt; 03-27-17 at 12:44 PM.
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Old 03-27-17, 12:18 PM
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Does this sound like a problem at the small white connector plug's junction to the board,or a problem at the control board?
 
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Old 03-27-17, 05:03 PM
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Does this sound like a problem at the small white connector plug's junction to the board,or a problem at the control board?
You should measure at least 12.6k on the board. Sounds like a problem in the connector.
The wire may have gotten pulled and broke the foils where the plug is soldered to the board.
If you have the ability.... cut off the plug and solder it directly to the board.

12.6k is perfect.
 
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Old 03-27-17, 08:52 PM
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Thanks for your patience,Pete!
Before I try your suggestion:

Question : Do you understand why, with the thermistor disconnected, measuring on the exposed 2 silver lead wires leaving the small white connector plug [before they travel to the 2 soldering points back of the control board], I get about 13K ohms?

I'm now not sure of the infinity reading on the 2 soldering points of the control board --it's very cramped!

It doesn't look like the foils are broken where the plug is soldered to the board.

I am pretty confident that the thermistor is not an "open" circuit.
 
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Old 03-27-17, 09:21 PM
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You measured the point on the board where the plug gets plugged in..... with the thermistor unplugged.... and you get an open or infiniti. Yes... that could be normal. A very high impedance circuit.

When you plug the thermistor in..... that same point on the board should now measure at least what the thermistor measures....around 13k.
 
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Old 03-28-17, 11:32 AM
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I realize, after all, that my AC IS COOLING [the compressor sounds like it's running & hot air is coming from the rear of the AC] in spite of the "Ambient Sensor" error & the fact that the temp is only 67 degrees.

Is this typical or reliable: that the AC will just continue running if there's a failed sensor/thermistor?

I might be able to live with this, if I thought that I could just turn On/Off the AC as needed.
 
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Old 03-28-17, 12:10 PM
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There isn't much technical support for those units so it's hard to say if the A/C will continue to run. I would think that the ambient air sensor would be to keep the unit from running if the surrounding air was too cold or too hot.
 
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Old 04-14-17, 04:05 PM
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SOLVED:Small white connector plug not firmly attached to 2 pins front side board

The problem was: the small white connector plug was not pushed down firmly enough onto the 2 pins on the front side of the control board!

While trying to put in a new Sensor I discovered that the whole small white connector plug [both halves] could be pulled off together, from the 2 pins that emerge from the front side of the board, so I reattached the white connector plug by pushing it down firmly onto the 2 pins.
-----------------------------------------------------------------------

These were all OK!:
1] The Ambient Sensor/Thermistor;
2] the soldering of small white connector plug to the back the board
3] the attachment of the white plastic end of the Sensor to the small white connector plug
------------------

Thanks for your help PJmax!
 
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Old 04-14-17, 04:51 PM
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You're welcome.... good job.
 
 

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