Fujitsu fan motor odd problem

[nike123]

Today I send this message to Fujitsu support:


I have one odd problem with Fujitsu ABY36RGA3W indoor unit fan motor. Outdoor unit is AOY36RCD3L.
On one object I have two of these units. One works perfectly OK and other have problem with air quantity thru indoor coil. When operation mode is set on fan mode and fan speed at high after switch on, fan starts at high speed and after approximately 10 seconds slow down to low speed and stay at that speed from there on. Measured at fan capacitor with digital multi meter (not TRUE RMS) I have at beginning 350V, and then voltage fall to 70V in 10 seconds, and stays at that level after that time. Power supply voltage is 222V measured with same instrument.
A same thing happens in Heat and Cool mode.

I changed fan motor and fan capacitor. That didn’t help.

After that, I swapped indoor unit PCB assemblies between these two identical indoor units, and that didn’t changed behavior of other unit, nor corrected problem on faulty one.

The indoor air temperature thermistor is not changed or swapped and filter PCB of indoor unit also did not changed or swapped.



Both indoor and outdoor unit have PCB and they communicate.

Does anyone have ever come across this or similar error?

To me it looks like some protective function on act which is not described in service instructions.

I give here link to electrical diagram and service instruction manual for this unit.

http://www.mediafire.com/?mdeo431sc9k

[paul_h]

nup, got me stumped. I was hoping it was a solid state fan relay or capacitor. doesn't seem to be the case though.
So voltage to the I/U doesn't dip low? mains feed to the o/u good (no undersized wiring, loose terminals, dodgy fuses)?
Does the compressor run happliy drawing the right current?
Is it possible to quickly run a test cable between the indoor and outdoor to verify interconnecting cable good?
is your 222v measured before of after the filter PCB?

[nike123]

nup, got me stumped. I was hoping it was a solid state fan relay or capacitor. doesn't seem to be the case though.
So voltage to the I/U doesn't dip low

Nope!


mains feed to the o/u good (no undersized wiring, loose terminals, dodgy fuses)?
Yep!


Does the compressor run happliy drawing the right current?
Yes!


Is it possible to quickly run a test cable between the indoor and outdoor to verify interconnecting cable good?Checked!


is your 222v measured before of after the filter PCB?At indoor unit terminal before filter PCB!

[Brian_UK]

I haven't seen the wiring diagram yet because of the file format, my end not yours...

Is there anything untoward with the neutral around this unit?

[Electrocoolman]

Nike,
You've changed fan motor, but have you changed complete fan assy....it's not the bearing at the other end of the fan assy thats seizing up?

[nike123]

Nike,
You've changed fan motor, but have you changed complete fan assy....it's not the bearing at the other end of the fan assy thats seizing up?

It is moving without any resistance and I changed bearings before (that was my first diagnose).

[nike123]

I haven't seen the wiring diagram yet because of the file format, my end not yours...

I could send it to you in different format if you wish, just say what you prefer.


Is there anything untoward with the neutral around this unit?

I dont understand what you mean by that.

[Brian_UK]

I could send it to you in different format if you wish, just say what you prefer.

I dont understand what you mean by that.

No, it's OK, I have downloaded a trial copy of RAR so have seen the files, thanks anyway.


Is the neutral feed to the unit secure, good. Voltage is being checked against the neutral and not the earth I assume. (Not trying to teach an old dog new tricks here, honest :) )

[nike123]

No, it's OK, I have downloaded a trial copy of RAR so have seen the files, thanks anyway.


Is the neutral feed to the unit secure, good. Voltage is being checked against the neutral and not the earth I assume. (Not trying to teach an old dog new tricks here, honest :) )

Yes, I checked voltage against neutral.
Now, when you mentioned that, I found that when I touch metal construction beneath air conditioner (which have no electrical contact with unit earth) with metal housing of PCB,small sparks appears and slight electric shock kicks my hand, who holds the housing.

I presumed that is some light fixtures, at that metal construction, have some leek toward earth, and when I touch it with housing (who have good earthing), current go thru housing to earth.
I don't see how that could influence work of fan, because this metal construction doesn't have any contact whit air conditioner when it is assembled.

[paul_h]

At indoor unit terminal before filter PCB!
Possible faulty filter PCB or dry solder joint on it?
Got me worried about that local dodgy electrics that's sparking nearby.
I'd be running a new active, neutral, earth test cable to the outdoor to verify clean power supply.

[australian tech]

ive got similar problem with an hitatchi 8kw. fan motor acts erratic,then stops to give a ten flash fault code(high indoor fan current) .i have changed motor , but am waiting for new indoor card... an electronics whiz i know,is checking the suspect card for me, with an oscillascope thingimyjig, and he reckons it might be an.."LM" chip (whatever that is) apparently it reads the moter amps and then spits out a signal for fault.......but dont know,could be well off the mark!!!! anyway im watchin this post with keen observance..

[nike123]

Possible faulty filter PCB or dry solder joint on it?

I don't see how filter PCB have effect on fan behavior. It is there to filter generated noise inside of the unit.
Also 350V can be measured because of actions of SSR.
If that is the case, I think that PCB would behave erratically on all functions, and not only on fan speed.
From observed, only fan speed error is present, and all other functions are perfectly OK.


Got me worried about that local dodgy electrics that's sparking nearby.
I'd be running a new active, neutral, earth test cable to the outdoor to verify clean power supply.

I am going to do that, just waiting answer from Fujitsu
support.

[nike123]

ive got similar problem with an hitatchi 8kw. fan motor acts erratic,then stops to give a ten flash fault code(high indoor fan current) .i have changed motor , but am waiting for new indoor card... an electronics whiz i know,is checking the suspect card for me, with an oscillascope thingimyjig, and he reckons it might be an.."LM" chip (whatever that is) apparently it reads the moter amps and then spits out a signal for fault.......but dont know,could be well off the mark!!!! anyway im watchin this post with keen observance..

In this Fujitsu, fan motor have small magnet on rotor and and hall element in housing of fan. That is detecting circuit for correct rotation speed of fan motor.
Fan speed is controlled by supplying fan with different pulse with thru solid state relay (SSR http://en.wikipedia.org/wiki/Solid_state_relay).
When sensed speed doesn't match, for predetermined time, those pulse with determined with control unit, and aplied thru SSR, control unit stops the fan and display error code on unit LED display.
Since fan motor is changed with new one, and control unit is on PCB (who is swapped with same unit on other identical air-con.) I conclude, that is nothing wrong with fan motor or control circuit. Fan acts upon power fed by SSR and that is controlled by main PCB and control circuit. If it is something wrong, it will be sensed and LED will be showing error code.
I simulated that with disconnecting control circuit, and after few seconds LED started displaying error.

Question is, why main PCB control fan at this way. Obviously, some input signal forces fan control to slow down to minimum speed, even in fan mode, and that is not described anywhere in service instructions for this unit.

[paul_h]

I was just looking at the part where you said you have a voltage drop, ie only 70v at the motor after ten seconds. Since you said the motor, capacitor and main PCB are good, I'm just looking at anywhere the mains could get a voltage drop. :)
It's a long shot, as you get no comms error or anything else getting a voltage loss/fault. But it's the fan motor that's going to put most stress on the system and show up any power supply issue first by not being able to draw enough current to run through hot or neutral wire.

I am going to do that, just waiting answer from Fujitsu
support. Thought you worked with them for a while?
First thing they normally say to me is make sure it's wired up properly, if in doubt, rewire it!
"Can't be their equipment at fault if it's acting wierd" :)

Let us know what fuji suggest, or what you find.

[nike123]

Today I was on site again and found that indoor heat exchanger thermistor is faulty (resistance is infinity).
That could be cause of problem.
I sent report to factory and asked confirmation that this fan behavior is caused by faulty thermistor because that is not explained in manual.
Also I am confused because there is no fault indication on LED-s of indoor unit (it should be 3 of 0,5s flashes/ 5s pause of operation LED and continuous 1 sec. flashing of timer LED, if sensor is open or shorted, according to service instruction manual).

[paul_h]

Welcome to the world of "there's fault code for everything, sometimes they don't work".
The last issue I had and posted here about ended up being exactly the same, faulty indoor thermistor on a panasonic. Yes, there a fault code for that, but it didn't activate! It's the path of least resistance, on most units an idoor senser sends a signal the slow compressor/fan or cut out compressor fan. It's a 50/50 whether you'll get the fault code or whether the unit will just deal with an over/under temp and display other problems. Mine just shut down thinking the evap was iced up, instead of giving thermistor error.
Hence my long standing attitude on them, research and look them up if it's flashing in your face, but don't rely on them to diagnose a system with strange operation.

[nike123]

I was just looking at the part where you said you have a voltage drop, ie only 70v at the motor after ten seconds. Since you said the motor, capacitor and main PCB are good, I'm just looking at anywhere the mains could get a voltage drop. :)


I don't think that is any voltage drop. That value on digital multimeter is because of SSR relay acting, and if I have scopemeter I will probably found that voltage is 220V but the wave has been cut off in some point by SSR relay.
I probably will acquire scopemeter in near future like this one:
http://www.uni-trend.com/UT81A.html
This tool becomes necessary these days with inverter power modules, switching power supply, indoor-outdoor communication, etc....

[nike123]

Answer about not indicating error from Fujitsu:


Thank you very much for your clear information and for your checking.

I can not understand that situation why the system did not show the error.
I need to check the logic of error detection with our design engineer.

As far as I know about the logic of error detection, the thermistor checking has be done when the Indoor pcb gets the power supply.
In my expelience, when I disconnect the thermister's connector from the controller PCB, the system did not show the error.
However, after the power supply reset, the Error was certainly indicated at that time.

But I guess that you have already done this way during the repairing so far. Isn't it ???
If that situation which you confirmed was correct, I have no idea now sorry.

Anyhow, I must make clear the timing of error detecting.

let me check that situation with our design engineer.
When I get any news about it, I will come back to you.

Thank you very much for your clear information.
Have a nice evening.

[ozairman]

Today I was on site again and found that indoor heat exchanger thermistor is faulty (resistance is infinity).
That could be cause of problem.
I sent report to factory and asked confirmation that this fan behavior is caused by faulty thermistor because that is not explained in manual.
Also I am confused because there is no fault indication on LED-s of indoor unit (it should be 3 of 0,5s flashes/ 5s pause of operation LED and continuous 1 sec. flashing of timer LED, if sensor is open or shorted, according to service instruction manual).

Sorry to come in late here but what you described sounded to me like the indoor fan running in "monitor mode" as happens when on heating and at setpoint temp, but I discounted this as you said the unit was set to fan only.

I have had issue with other Fujitsu of this era AR*36RLA3 with defective indoor pipe thermistor causing erratic undocumented operation. In the case I resolved it was causing the outdoor to cycle off then not cycle on again on heating. Investigation found that the pipe sensor was giving the impression to the indoor control pcb that the coil was too hot, therefore causing outdoor fans to stop 1st (heating overload protection) and then as room temp warmed up the outdoor unit to stop completely. This was after service company had already replaced IU PCB, OU PCB, OU Thermistors and 4 way valve!!!

I have AR*36RLA3 at my own home, I spent a few hours in my roof one night monitoring thermistor input voltage of pipe thermistor which helped diagnose above problem. I also found out that I could disconnect or even short out IU pipe thermistor and it would not trigger an error!!:eek:
Yet if I disconnected or shorted a thermistor on the ODU it would immediately stop and bring up thermistor fault. Sometimes I think that gremlins get into old units

[nike123]

Sorry to come in late here but what you described sounded to me like the indoor fan running in "monitor mode" as happens when on heating and at setpoint temp, but I discounted this as you said the unit was set to fan only.

I have had issue with other Fujitsu of this era AR*36RLA3 with defective indoor pipe thermistor causing erratic undocumented operation. In the case I resolved it was causing the outdoor to cycle off then not cycle on again on heating. Investigation found that the pipe sensor was giving the impression to the indoor control pcb that the coil was too hot, therefore causing outdoor fans to stop 1st (heating overload protection) and then as room temp warmed up the outdoor unit to stop completely. This was after service company had already replaced IU PCB, OU PCB, OU Thermistors and 4 way valve!!!

I have AR*36RLA3 at my own home, I spent a few hours in my roof one night monitoring thermistor input voltage of pipe thermistor which helped diagnose above problem. I also found out that I could disconnect or even short out IU pipe thermistor and it would not trigger an error!!:eek:
Yet if I disconnected or shorted a thermistor on the ODU it would immediately stop and bring up thermistor fault. Sometimes I think that gremlins get into old units

What coincidence in timing your post!:)
I just been today at site and rechecked indoor unit sensors with new probes for universal instrument capable to touch these small connectors of them. It is found that both sensors are OK (obviously my first measurements are not successfully because of inadequate probes).
Then I changed thermistors with new ones and still behavior of fan remains the same.
When I disconnect probes unit, immediately after power up, start to signaling fault probe error.
I am only left with grounding error possibility, and in few days I am going to put new supply and interconnect cable for test purpose.

[ozairman]

What coincidence in timing your post!:)
I just been today at site and rechecked indoor unit sensors with new probes for universal instrument capable to touch these small connectors of them. It is found that both sensors are OK (obviously my first measurements are not successfully because of inadequate probes).
Then I changed thermistors with new ones and still behavior of fan remains the same.
When I disconnect probes unit, immediately after power up, start to signaling fault probe error.
I am only left with grounding error possibility, and in few days I am going to put new supply and interconnect cable for test purpose.

I will try and look back through my note books for the thermistor voltages I recorded. I find they are most useful especially if you can get hold of the thermistor voltage tables. Sharp needlepoint probes for your multimeter are very useful!

One last thought and this may sound stupid but what remote controller is this system using? Wired wall mounted, Infra red wall mounted or Infra red hand held? If Infra red type does it have a slide switch to change between cooling and heating modes and does it have auto changeover in mode setting?

[nike123]

I will try and look back through my note books for the thermistor voltages I recorded. I find they are most useful especially if you can get hold of the thermistor voltage tables. Sharp needlepoint probes for your multimeter are very useful!

As I wrote earlier, I interchanged PCBs with other identical unit and yesterday I changed thermistors wit new ones.


One last thought and this may sound stupid but what remote controller is this system using? Wired wall mounted, Infra red wall mounted or Infra red hand held? If Infra red type does it have a slide switch to change between cooling and heating modes and does it have auto changeover in mode setting?Remote controller is infra red hand held, and I tried with other from other identical unit with no difference in behaving. Mode setting is with mode button (no slide).

[ozairman]

As I wrote earlier, I interchanged PCBs with other identical unit and yesterday I changed thermistors wit new ones.

Remote controller is infra red hand held, and I tried with other from other identical unit with no difference in behaving. Mode setting is with mode button (no slide).

That must be big flat 4xAAA battery type remote? on earlier remotes with slide switch for mode change often the brass contacts inside the remote come adrift from the slide switch that does fan, heat, cool, auto selection. The default is auto mode (no contacts bridged) and the indoor fan appears to have a mind of its own :).

What happens if you disconnect the fan motor feedback plug from the control pcb? does the fan speed up or slow down also what sort of DC Voltages do you get between pins 2-3 of feedback plug does it vary with the fan speed changing? and how does these compare with the other unit that is working?

[nike123]

Update at this failure.
I found that connecting cable between fan terminals and PCB has wrong wire positions at connector on one end.
It is probably that connector pins are fall of during indoor unit washing (unit was totally dismantled and washed in parts) and my apprentice (who made washing) has wrongly put back wires in connector.:mad:
It cost me 5 uncharged trips, 5 months and one unnecessary changed fan motor ( 200€ on my expense) to solve the problem. :eek:

Do not assume that something is OK, check it! That is my lesson from this (and many other) case.:o
I checked conductivity but never that wires are placed in connector as they should be.

Unit has worked whole summer with fan at max speed without possibility to turn off or change fan speed (i made jumper wire between SSR contacts). That only say how resilient is this fan motor to survive 4 month non stop work with switched main and auxiliary winding without any damage.

[rannoch]

I have the same symptoms with a Fujitsu AST24PBA-W. Plenty of heat available but the fan won't go to high speed to blow it out. Have replaced the pipe sensor with a variable resistor and can make the unit function correctly. Dont have resistance data for the pipe sensor but will get a replacement & post the outcome.

[nike123]

. Dont have resistance data for the pipe sensor but will get a replacement & post the outcome.

Good, I wait for your result.
Here are resistances. As we learned, you need to check that resistance is continuous in whole thermistor range without any sudden discrepancies from curve (max 10%, but continuous).
http://i54.tinypic.com/2wresz5.jpg

[El Padre]

Hi Nike,

This has been an interesting one, have you got a decade/resistance box, which would allow you to input a chosen resistance into a PCB if you have a suspect thermistor.

I am interested in the portable oscilloscopes myself, it would make an interesting thread if you decide to get one.

Cheers

[nike123]

Hi Nike,

This has been an interesting one, have you got a decade/resistance box, which would allow you to input a chosen resistance into a PCB if you have a suspect thermistor.

No! I don't think that is necessarily to go that way.




I am interested in the portable oscilloscopes myself, it would make an interesting thread if you decide to get one.

CheersI also would like to have portable oscilloscope (especially Fluke 900 series or at least 123), but if you think that that will sort thermistor problem, I am sure that will not be more helpful than good multimeter.

[El Padre]

No! I don't think that is necessarily to go that way.

I also would like to have portable oscilloscope (especially Fluke 900 series or at least 123), but if you think that that will sort thermistor problem, I am sure that will not be more helpful than good multimeter.

I mentioned the decade box because it gives you the possibility of forcing systems on, in the event of a thermistor failure, which can sometimes be useful.

I did not intend to suggest that the scopemeter would have been of more use than a multimeter in this case, just that I am interested in getting one myself, will have a look at the 900 series.:cool:

Cheers

[rannoch]

Hi guys, after an excruciating wait for parts I have finally installed a new pipe sensor and everything is back to normal. Thanks to nike123 for the sensor data - wish I had had it when this first started. As we can see from the temperature v's resistance graphs the sensor has a negative temperature coeficient ie. as temp goes up resistance comes down. The old sensor got down to 12 k ohms as the coil temp increased - then went open circuit!! I can only guess this sent the unit into a frenzy thinking that it had all of a sudden iced up inside and plow more heat in and reduce the fan to monitor speed to defrost it?? Regarding the variable resistance - I used a 100kohm potentiometer & soldered it onto a suitable plug & manually controlled unit for the 4 weeks it took to get a replacement part. Thermistors can always be replaced this way (with a potentiometer) as a substitute to test the operation. There is no need for a scope - it wont tell you anything - a multimeter will give the whole story. Cheers everyone

[nike123]

Still, I would like to have scope meter.;);)