Inverter fault? Advice please

[reasonable]

Hi I hope someone can help. I have recently had a Daikin 9kw split system inverter unit installed. I noticed that it takes a long time to cool the room and would not reach anything like 18 deg C on that setting even from 26 deg start.

So I have checked the power input, when it should be on maximum, on a number of occasions and found that it’s only taking less than half its rated input power.

The c.o.p. is 2.7 so the input power should be 3300 W at rated capacity. The maximum it will ever reach is 1800 W. The Daikin agent checked out the unit and said he could not find a fault. He also said it will never ramp up to full power as long as there is an 11 degee C temperature drop across the coil (which there was at the time).

My calculations, based on the specification max airflow rate of 352 litres/sec and using the 11 deg drop come to a cooling power of 4640 W making an input power of 1720 W which agrees with my power measurement.

So I conclude that the Daikin agent is wrong and the unit will only work at about half rated capacity.

The Daikin technician is coming in a couple of weeks to give a “second opinion” on the unit. Do you agree that the unit is faulty and if so how can I convince the Daikin technician that this is the case (assuming that he also finds no fault)?

Regards

Has anyone got the service manual for this FTXS90FVMA/RXS90FVMA or tell me how to get it?

[nike123]

The unit is controlled by thermistors and their readings. If their reading is faulty, control of unit is also faulty.

To check this, allow room to heat up (open windows and doors for half our) and then set temperature at remote to 18°C. Also, set fan at high!
After some time (do not close windows) check temperature (and humidity if it is humid and you have condensation dripping at condensate pipe outlet) at above the air conditioner and at air exit and post here.

If you don't have humidity meter than you could wrap thermometer tip with piece of wet gauze to obtain wet bulb temperature.

For example, if you have day with 30°C DB and 50% humidity (22°C DB)and fan is at high (352 l/s when filter and evaporator is clean and fan is OK) then you will have discharge air of 15°C DB and 100% humidity (15°WB) for full capacity of that AC of 9,2kW at sea level (6 kW sensible and 3,2 kW latent).

On the other hand, If you have day with 70% humidity at 30°C then air off temperature should be around 20°C.

What is room size and construction, it looks big AC for "normal" room.

[reasonable]

The unit is controlled by thermistors and their readings. If their reading is faulty, control of unit is also faulty.

To check this, allow room to heat up (open windows and doors for half our) and then set temperature at remote to 18°C. Also, set fan at high!
After some time (do not close windows) check temperature (and humidity if it is humid and you have condensation dripping at condensate pipe outlet) at above the air conditioner and at air exit and post here.

If you don't have humidity meter than you could wrap thermometer tip with piece of wet gauze to obtain wet bulb temperature.

For example, if you have day with 30°C DB and 50% humidity (22°C DB)and fan is at high (352 l/s when filter and evaporator is clean and fan is OK) then you will have discharge air of 15°C DB and 100% humidity (15°WB) for full capacity of that AC of 9,2kW at sea level (6 kW sensible and 3,2 kW latent).

On the other hand, If you have day with 70% humidity at 30°C then air off temperature should be around 20°C.

What is room size and construction, it looks big AC for "normal" room.

Hi Thanks for your reply. The room is a fairly large one and 9kw is about right. As I said I am basing my belief that the unit is faulty because it cannot be made to ramp up to its rated input power. This would not happen even last week when the outside temperature was 46 degrees!

[nike123]

Hi Thanks for your reply. The room is a fairly large one and 9kw is about right. As I said I am basing my belief that the unit is faulty because it cannot be made to ramp up to its rated input power. This would not happen even last week when the outside temperature was 46 degrees!

It doesn't matter what is outside, it matters what is inside, so make measurements as I suggested, just to be sure.

[laf100]

As far as I am aware, Daikin inverters will ramp up/down the compressor frequency to try and achieve a target evaporating temp' (determined by a formula built into the software) if the C/U L/P transducer is reading the correct evap' temp (or THINKS it is) the compressor will not ramp up any further. Check the suction pressure transducer calibration. Also pressure & air on/off the evap' coil may help others to diagnose/assist you.

[Gary]

An 11K delta-T (drop across the coil) is normal and entirely appropriate for your system, but this doesn't tell us the whole story. The warmer the air entering the coil, the harder the system must work to achieve that 11K dT... so we need to know the temperatures entering and leaving the coil.

[reasonable]

The unit is controlled by thermistors and their readings. If their reading is faulty, control of unit is also faulty.

To check this, allow room to heat up (open windows and doors for half our) and then set temperature at remote to 18°C. Also, set fan at high!
After some time (do not close windows) check temperature (and humidity if it is humid and you have condensation dripping at condensate pipe outlet) at above the air conditioner and at air exit and post here.

If you don't have humidity meter than you could wrap thermometer tip with piece of wet gauze to obtain wet bulb temperature.

For example, if you have day with 30°C DB and 50% humidity (22°C DB)and fan is at high (352 l/s when filter and evaporator is clean and fan is OK) then you will have discharge air of 15°C DB and 100% humidity (15°WB) for full capacity of that AC of 9,2kW at sea level (6 kW sensible and 3,2 kW latent).

On the other hand, If you have day with 70% humidity at 30°C then air off temperature should be around 20°C.

What is room size and construction, it looks big AC for "normal" room.

I’ve taken a series of readings today as requested over a period of about 20 mins on "powerful" set out below (not at regular intervals). I used electronic sensors which both read the same values when put together.

Inlet temp RH Outlet temp RH
25.6 44 17 72
24.6 45 15.6 76
24.1 46 14.9 78
23.6 47 14.4 81
23.3 47 14.0 81

I noticed when monitoring the power input yesterday that the power shot up twice – once for about 5 seconds and then a few minutes later for about 10 seconds. It was too quick to take a measurement but was about what I would have expected if the unit was fully ramped up. So I wonder if there might be a loose connection somewhere in the sensing circuits?

Thanks all in anticipation of your comments.

[nike123]

Inlet temp RH Outlet temp RH
25.6 44 17 72
4 kW 0,9SHF

24.6 45 15.6 76
Same as above

24.1 46 14.9 78
4,4kW 0,87 SHF

23.6 47 14.4 81
4,2kW 0,92 SHF

23.3 47 14.0 81
Same as above

[nike123]

I noticed when monitoring the power input yesterday that the power shot up twice – once for about 5 seconds and then a few minutes later for about 10 seconds. It was too quick to take a measurement but was about what I would have expected if the unit was fully ramped up. So I wonder if there might be a loose connection somewhere in the sensing circuits?

Probably it is indoor return air thermistor faulty or Indoor PCB because unit behave as that constant indoor temperature is maintained.

[laf100]

I would say this unit is short of refrigerant, when it was commisioned was the additional refrigerant correctly calculated & added? If so it's possible the outdoor may not have had the correct base charge added at the factory- I have had that previously.
IMHO I would reclaim, pressure test, triple vac & recharge with virgin gas.
Inverter splits tend to "mask" refrigerant shortages because they adjust the frequency to compensate for the pressure drop.

[reasonable]

Inlet temp RH Outlet temp RH
25.6 44 17 72
4 kW 0,9SHF

24.6 45 15.6 76
Same as above

24.1 46 14.9 78
4,4kW 0,87 SHF

23.6 47 14.4 81
4,2kW 0,92 SHF

23.3 47 14.0 81
Same as above

Many thanks
I think you are confirming my previous measurements and that the system is behaving like a 4kw unit rather than a 9kw as specified.

[brunstar]

hi reasonable,
in relation to your air conditioning unit.
Are you running it on high fan speed all of the time, as this is a must for the unit to evaporate the liquid out of the indoor coil for it to ramp up.
i feel as though you may either have a gas problem with the system or the condensing unit is recirculating around the outdoor unit.
Do you have anything under the indoor unit and what is around the outdoor unit.
what is the length of pipe between the indoor and out also.
If the system is short of refrigerant it will go into what you call drooping mode which will be less than half the speed of the unit so that the unit does not over heat by maintaining good superheat..

let me know a bit about your installation and you can go from there.

cheers.

[Thermatech]

If the system is slightly SOG & compressor discharge is at max temp then the compressor will stay at slow speed until the discharge temp falls back a bit.
then
The compressor will ramp up but will straight away hit max discharge temp & slow back down again.

This limits cooling capacity at indoor unit but does not produce fault code as system is trying to cope.

Suggest get technican to measure interconnect pipe lenght & calculate trim charge.
Then
Recover refrigerant & confirm correct charge.

[al]

one other to consider, unit is exibiting symptoms of being in test mode(not too familiar with Daikin test mode thou) ie comp limited to 50% capacity,is the indoor casing pushing on the emergency override button?

al

[Temprite]

As far as I am aware, Daikin inverters will ramp up/down the compressor frequency to try and achieve a target evaporating temp' (determined by a formula built into the software) if the C/U L/P transducer is reading the correct evap' temp (or THINKS it is) the compressor will not ramp up any further. Check the suction pressure transducer calibration.

I had a Daikin inverter not ramping up and this was the cause pretty easy to check.

[reasonable]

hi reasonable,
in relation to your air conditioning unit.
Are you running it on high fan speed all of the time, as this is a must for the unit to evaporate the liquid out of the indoor coil for it to ramp up.
i feel as though you may either have a gas problem with the system or the condensing unit is recirculating around the outdoor unit.
Do you have anything under the indoor unit and what is around the outdoor unit.
what is the length of pipe between the indoor and out also.
If the system is short of refrigerant it will go into what you call drooping mode which will be less than half the speed of the unit so that the unit does not over heat by maintaining good superheat..

let me know a bit about your installation and you can go from there.

cheers.

Hi

The indoor unit is mounted at height of 2.3m in a 3.5m high room. The outdoor unit is directly above it on the roof so fairly short pipe lengths – say 2 or 3 metres. When looking or testing for maximum power the fan speed is maximum on “powerfull” mode. There is plenty free space around both units.

The Daikin agent drained the gas and recharged the unit but this did not make any difference to performance – so I assume the gas system is fully charged.

Having now tried coolpack I find that the temperature drop across the coil should be between 14 and 16 degrees to give 9kw cooling power. Does this sound right?

Regards

[al]

A 2 to 3m pipe run is very short,is it over charged?

al

[kelvin01]

Hi there.

I had a similar porblem with a MHI unit in a computer room in a school. An engineer had been before me and was condemning the compressor and alsorts.

I went and took the system back to basics, reclaimed all refrigerant and pressure tested. No leak and it was down to incorrect factory charge.

I would try this step first and then check what charge the daikin engineer has put in the system because i know daikin recommend you take out refrigerant from the system for such short pipe runs as the system will struggle to operate overcharged.

[laf100]

I am fairly sure most Daikin units have a minimum recommended pipe run of 5M. If posiible try to download the installation manual for this system from Daikin Extranet,and check. You are right that one can usually expect around 14 DT across the evap coil on this unit. Did you definatley quote the correct M/N in your OP? In the UK a size 90 outdoor is usually a Multi-Split?

[nike123]

Having now tried coolpack I find that the temperature drop across the coil should be between 14 and 16 degrees to give 9kw cooling power. Does this sound right?

Regards

That depend on SHR (sensible heat ratio) which depend on indoor room humidty and evaporator TD!
Check Evaporator UA module in Coolpack.

Also, good software for evaluaation is this one.

[nike123]

If the system is slightly SOG & compressor discharge is at max temp then the compressor will stay at slow speed until the discharge temp falls back a bit.
then
The compressor will ramp up but will straight away hit max discharge temp & slow back down again.

I think that that behavior will require some longer times for pipes to heat and thermistors to react, than 5-10 seconds reported by original poster.

I am more leaned to possibility that some current in inverter is rising more than allowed and therefore such fast reaction. Or pressure sensors are mounted and control logic is acting upon them.

[reasonable]

I am fairly sure most Daikin units have a minimum recommended pipe run of 5M. If posiible try to download the installation manual for this system from Daikin Extranet,and check. You are right that one can usually expect around 14 DT across the evap coil on this unit. Did you definatley quote the correct M/N in your OP? In the UK a size 90 outdoor is usually a Multi-Split?

I cannot see any reference to minimum pipe run - only maximum. The unit is definitely 9kw. When the original installation was done the larger diameter pipe was kinked and a new piece had to be welded on. Also the smaller dia pipe had no connector which also had to be welded on. Could this have any relevance to the performance by possibly restricting refrigerant flow?

[laf100]

I am not entirely sure what you mean by " the small diameter pipe had no connector". There are flare connections at the outdoor and fan coil of all split systems in the UK, if you suspect a restriction, yes this will affect performance, are you certain the pipe sizes are correct? What discharge and suction pressure do you have?

[reasonable]

I am not entirely sure what you mean by " the small diameter pipe had no connector". There are flare connections at the outdoor and fan coil of all split systems in the UK, if you suspect a restriction, yes this will affect performance, are you certain the pipe sizes are correct? What discharge and suction pressure do you have?

The smaller pipe is the liquid pipe which came as just normal pipe end without the flare connection. The larger gas pipe was repaired because of the kink. So I just wondered whether the repairs/joins may have some effect.

[reasonable]

Hi I hope someone can help. I have recently had a Daikin 9kw split system inverter unit installed. I noticed that it takes a long time to cool the room and would not reach anything like 18 deg C on that setting even from 26 deg start.

So I have checked the power input, when it should be on maximum, on a number of occasions and found that it’s only taking less than half its rated input power.

The c.o.p. is 2.7 so the input power should be 3300 W at rated capacity. The maximum it will ever reach is 1800 W. The Daikin agent checked out the unit and said he could not find a fault. He also said it will never ramp up to full power as long as there is an 11 degee C temperature drop across the coil (which there was at the time).

My calculations, based on the specification max airflow rate of 352 litres/sec and using the 11 deg drop come to a cooling power of 4640 W making an input power of 1720 W which agrees with my power measurement.

So I conclude that the Daikin agent is wrong and the unit will only work at about half rated capacity.

The Daikin technician is coming in a couple of weeks to give a “second opinion” on the unit. Do you agree that the unit is faulty and if so how can I convince the Daikin technician that this is the case (assuming that he also finds no fault)?

Regards

Has anyone got the service manual for this FTXS90FVMA/RXS90FVMA or tell me how to get it?

Why is no fault code displayed?

[nike123]

Why is no fault code displayed?

Because control logic doesn't see that as error!

[reasonable]

Hi I hope someone can help. I have recently had a Daikin 9kw split system inverter unit installed. I noticed that it takes a long time to cool the room and would not reach anything like 18 deg C on that setting even from 26 deg start.

So I have checked the power input, when it should be on maximum, on a number of occasions and found that it’s only taking less than half its rated input power.

The c.o.p. is 2.7 so the input power should be 3300 W at rated capacity. The maximum it will ever reach is 1800 W. The Daikin agent checked out the unit and said he could not find a fault. He also said it will never ramp up to full power as long as there is an 11 degee C temperature drop across the coil (which there was at the time).

My calculations, based on the specification max airflow rate of 352 litres/sec and using the 11 deg drop come to a cooling power of 4640 W making an input power of 1720 W which agrees with my power measurement.

So I conclude that the Daikin agent is wrong and the unit will only work at about half rated capacity.

The Daikin technician is coming in a couple of weeks to give a “second opinion” on the unit. Do you agree that the unit is faulty and if so how can I convince the Daikin technician that this is the case (assuming that he also finds no fault)?

Regards

Has anyone got the service manual for this FTXS90FVMA/RXS90FVMA or tell me how to get it?

The latest is that a Daikin engineer came and recognises that the fault is that the unit will not ramp up. But he is not sure why and had replaced the gas. He thinks it may be the inverter board in the outdoor unit and will try replacing this next week.

Regards

[back2space]

Is it not the Outdoor Main PCB thats faulty.

If the max it will reach is 1800w then it must be ramping up to some sort of leve.

It seems that there is problem with the control of the system because obviously its ramping up from nothing to 1800W.

Ive been told that if its the inverter board thats faulty the compressor wont run at all.

If its the main PCB thats faulty then the compressor will not ramp up and down properly. Software error.

Having same probs with my system in heating, installer says its the main PCB as its erratic and the inverter seems to ramp up when it doesnt need to be outputting higher and then temp overshoots and it cycles off rather than ramping down.

If i run 2 units at the same time the compressor runs slower than it should meaning capacity drops across the system if only one unit is demanding heat meaning the air off temp drops about 10C so the room struggles to reach set point on cold days.

Im told its the main PCB at fault and this is going to be replaced and that LG have been advised to look at the programming of the software.

As if I only have one unit running it shouuld be using less power than if i have two running.

Currently if I have one unit running the system draws 1300watts at lowest point with air off of 49C but if i switch two units on but only 1 is demanding heat the system runs at 950watts with air off of about 35C.

Crazy!

[Temprite]

The latest is that a Daikin engineer came and recognises that the fault is that the unit will not ramp up. But he is not sure why and had replaced the gas. He thinks it may be the inverter board in the outdoor unit and will try replacing this next week.

Regards

Get him to check suction transducer. You need a good set of gauges and multimeter

[cool_tech]

hey guys,
just a thought if nitro wasnt bled through lines could a small capillary line on the evap be blocked??