Fujitsu ao54 VRF system

[paul_h]

I went to a system today that had one of these 'j' series inverters feeding a ao36ufaar upstairs and a ao25ufaar downstairs.

First major complaint was the upstairs doesn't cool at all. I found the problem to be a bad thermistor plug on the i/u PCB (it was bent so pin on plug damaged), and no liquid getting past the valve.

After fixing that, the tx valve opened up and there was a 27C on, 15C off through the coil.

I looked at the outdoor unit, LEDs 3,4,6 were flashing five times.
LED3 x5 = 50% capacity
LED4 x5 = ?
LED6 x5 = compressor protection activated. This is what I need help with.

I turned the downstairs unit off and the compressor speed dropped off to 30%, then the LED6 stopped flashing.

LP 1000kpa
HP 2900kpa
o/u air (on/off) was 33/44C
Discharge temp was 60C
Mains amps was 18.5A.
Amps at compressor 19.5A

So, questions to all the fuji guys out there. Why was speed limited? Why did it only run at 30% when protection dropped off when it had a 18C setpoint and it was 27C in the room?

Also it had a wierd set up inside, the units used regular fuji infrared remote comtrollers, with recievers on the ceiling instead of the wall controllers, so no error codes could be gotten from the indoor units.

[nike123]

Did you reset the unit?

[paul_h]

Yes, even though the LED6 stopped flashing when I switched off the downstairs unit, I reset the unit.
When turned back on and only the upstairs unit on, it would only run at 30%, even though the setpoint was 18C and the indoor temp was 27C.
All the measurements were the same, just LED6 stopped flashing, though LED4 was still flashing

[nike123]

Did you checked indoor air sensor resistance and compared with R/T diagram?

[paul_h]

Would that cause LED6 to flash 5 times indicating the compressor is in protection mode?
I'm working on two problems here, one is the air sensor plug was faulty, not opening the valve, still hoping to get a replacement board from fujitsu for that one. So no, I don't trust the indoor sensor reading. The other is this compressor protection mode, I just want to know what usually causes it.

edit: Also, resistance is near useless IMHO, sure it shows gross faults, but not whether a sensor will be 100% good.
Being in the refrigeration game as well as airconditioning, I know so many faulty sensors will pass testing with a mulitmeter in ohms, but fail sending the right signal to the controller.
It's the volts the controller sees that really matters, not the resistance that your mulitmeter reads. Anyway of getting tables for voltage across these sensors at certain temps?
I'd love to have that info, way more accurate and easier to do while the unit is still running as well.

[nike123]

Would that cause LED6 to flash 5 times indicating the compressor is in protection mode?
I'm working on two problems here, one is the air sensor plug was faulty, not opening the valve, still hoping to get a replacement board from fujitsu for that one. So no, I don't trust the indoor sensor reading. The other is this compressor protection mode, I just want to know what usually causes it.


I am going to check manual!


edit: Also, resistance is near useless IMHO, sure it shows gross faults, but not whether a sensor will be 100% good.
Being in the refrigeration game as well as airconditioning, I know so many faulty sensors will pass testing with a mulitmeter in ohms, but fail sending the right signal to the controller.
It's the volts the controller sees that really matters, not the resistance that your mulitmeter reads. Anyway of getting tables for voltage across these sensors at certain temps?
I'd love to have that info, way more accurate and easier to do while the unit is still running as well.

It is not voltage that changes at thermistor leads. Controller supply certain tension ( measure it on terminal) and that voltage (tension) draw current thru thermistor. As temperature change, also current change accordingly, not tension. Then, that current is translated in digital value at analog to digital converter.

[paul_h]

Here's my experience in refrigeration systems:
Manufacturer gives value of thermistor in volts and ohms for a specific temperature. Test it with a meter, and you can get a good reading in OHMs.
The chart they sometimes supply also gives what voltage you'd see across the sensor, test it with that and it fails.

I've seen that time and time again because other people still use the resistance test, pronouce the thermistor good and can't fix it.
I test the voltage across the sensor and find it faulty straight away. Sometimes the sensor shows up good with a multimeter, but can't flow the current through it to show the right voltage is what I meant. Are you saying that or something different?
By voltage difference across the thermistor I am of course testing current flow through the thermistor. Voltage is known from the PCB output, resistance can be measured and test OK, but if the sensor is degraded and can't flow that current, voltage will be off.
Not only that, but voltage testing is easier and quicker as you don't have to turn the unit off etc.
I think it was a fuji tech that showed me this in the first place, as even they had problems with damaged sensors showing good resistance but failing voltage tests. The only problem is it's hard to get voltage data for most thermistors.
But I use it everyday for the few manufacturers that supply it in refrigeration, (more likely to see this problem due to extreme cooling/heating of the thermistor), and get heaps of problems fixed that most other techs can't find because they only use resistance tests

[nike123]

If Led1 flashes 0,1s on/o,1s OF and :
LED4 5 flashes =Electric current trip
LED6 5 flashes =Indor unit 4 error

Indoor unit room temperature sensor:

http://farm3.static.flickr.com/2175/2229986181_b0a5bb16f7_b_d.jpg

Electric curent trip:

http://farm3.static.flickr.com/2079/2229985949_9341cde7d5_b_d.jpg

Also, check address settings!

[nike123]

It seems that you fixed thermistor problem when you inserted thermistor plug properly (led 6 not flash any more).
But it is still electrical current trip active (led 4 flashes 5 times)

[nike123]

Here's my experience in refrigeration systems:
Manufacturer gives value of thermistor in volts and ohms for a specific temperature. Test it with a meter, and you can get a good reading in OHMs.
The chart they sometimes supply also gives what voltage you'd see across the sensor, test it with that and it fails.

I've seen that time and time again because other people still use the resistance test, pronouce the thermistor good and can't fix it.
I test the voltage across the sensor and find it faulty straight away. Sometimes the sensor shows up good with a multimeter, but can't flow the current through it to show the right voltage is what I meant. Are you saying that or something different?
By voltage difference across the thermistor I am of course testing current flow through the thermistor. Voltage is known from the PCB output, resistance can be measured and test OK, but if the sensor is degraded and can't flow that current, voltage will be off.
Not only that, but voltage testing is easier and quicker as you don't have to turn the unit off etc.
I think it was a fuji tech that showed me this in the first place, as even they had problems with damaged sensors showing good resistance but failing voltage tests. The only problem is it's hard to get voltage data for most thermistors.
But I use it everyday for the few manufacturers that supply it in refrigeration, (more likely to see this problem due to extreme cooling/heating of the thermistor), and get heaps of problems fixed that most other techs can't find because they only use resistance tests


Control PCB of Fujitsu suply 5VDC to thermistor. That tension is stable unless we have thermistor insulation or wires to thermistor insulation damaged and in contact with ground point of PCB. If that is a case, then current protection circuit in integrated circuit who converts analog value (current) of termistor to digital value acts and lovers tension to thermistor in order to prevent overcurent threw thermistor and Analog to Digital circuit.
So, when you measuring voltage at thermistor you will measure 5V no matter what resistance (and temperature) is that thermistor.
If analog to digital converter is defective or insulation of thermistor or belonging wires you could mesure different value.
You could calculate current when you know resistance (look at R/T chart) of thermistor and voltage of circuit (5VDC) and compare it with actual (measured ) current. That way you are established that analog part of temperature aquiring circle is working OK.

[paul_h]

Control PCB of Fujitsu suply 5VDC to thermistor. That tension is stable unless we have thermistor insulation or wires to thermistor insulation damaged and in contact with ground point of PCB. If that is a case, then current protection circuit in integrated circuit who converts analog value (current) of termistor to digital value acts and lovers tension to thermistor in order to prevent overcurent threw thermistor and Analog to Digital circuit.
So, when you measuring voltage at thermistor you will measure 5V no matter what resistance (and temperature) is that thermistor.
If analog to digital converter is defective or insulation of thermistor or belonging wires you could mesure different value.
You could calculate current when you know resistance (look at R/T chart) of thermistor and voltage of circuit (5VDC) and compare it with actual (measured ) current. That way you are established that analog part of temperature aquiring circle is working OK.
Thanks for all your help, but I'm still not following you here with voltage reading not being possible.
Attached is a chart from another manufacturer that sends a 5v DC signal to a thermistor. As well as the resistance value, they have also given the voltage value, and it's easily measured with a mulitmeter across the thermistor. Measuring resistance for this equipment sometimes gives a false good sensor, measuring voltge is 100% proof testing.
I have in fact been given values for other fujitsu sensors in the same way, being told to test the voltage with a mulitmeter. Ie not being told just to test with faults, but to write down voltages to get the temp they are reading, fault or no fault.

Thanks for all the help again, the outdoor saying thermistor error makes a lot more sense than what my manual told me.

edit: Second attachment here is from fujitsu giving thermistor voltage values to check thermistor, so it can be done, even with fujitsus

[nike123]

I see! I was assumed (something what I rarely do) that in Fujitsu, they use circuit as I described.
Maybe they don't, and you could do find different voltage for deferent resistance of thermistor.
That is possible if circuit for thermistor is consisted of two serial resistors. One is in integrated circuit and other is thermistor . That way, you could have different voltage with different temperature (resistance) of thermistor. Also, that way input is protected from short cycle.
In serial connected resistors, if one is fixed and one is varying, voltage at that resistor is changing as resistance is changing but source voltage stays unchanged (sum of voltage drops across both of resistors is equal to that of source). That is Ohm law.
I personally, never measured voltage nor see chart like this, but I always found defected thermistor of this type (2 wire 10KOhm NTC) measuring only resistance.
This is new to me, that one cannot be sure in only measuring resistance of 2 wire NTC probes.

Where did you find that second table? Could I got one readable?

[ozairman]

Been real busy lately hottest summer in 16 years where I am as Paul_h will know, hopefully you are surviving better than I am. I missed this one and nobody at your old place bounced it to me either :-(. Led 6 flashing 5 times on a J series indicates "compressor rotation speed protection" as you have already worked out. The fun part is working out which item is actually causing the protective function to occur as there are multiple causes as below:
-Discharge temp protection >108degC (not likely as you say disch temp is only 60degC
-Cooling overload protection - OU coil midpoint above 59degC,
- Current draw protection.
All of which will cause the speed of the comp to be slowed down until the parameter drops below the threshold value then the protection will be released.
As for why the unit would only operate at 30% I cannot say the logic for Comp speed vs IU operation, demand is proprietary stuff that I can't even get hold of :-(. I normally tend to look at superheat and if it about 0K then the unit is probably doing what it thinks is correct for that condition. The systems don't really overboost their capacity if there is less IU capacity operating than the OU capacity available.

Sorry this is not much help now