Daikin Multi Split 3MXS68G2V1B

[moondawn]

Hi all

I been called to the above system has two indoor units connected. the error code U0 i think which equates to shortage of refrigerant. noticed suction was at 12 bar on r410a this is inverter however and that coil are off temps were around 10 deg diff.

tried on heat mode would not reach its target condensing temp of 28 bar was around 24 bar.

spoke with daikin about possible sensors causing this problem as the unit runs for a while then goes into fault.

first daikin guy said check sensors which i said i have the app on my phone for and i can get the resistances from there. he said the discharge temp thermistor on the app is different to all the air and coil thermistors however for this unit it is the same as an air or coil thermistor so will not read like the normal discharge thermistor which is around 10x a normal resistance reading. he said the bigger systems sky air and vrv require reading the discharge thermistor section 10x reading. however it does not mention this on the app.

carried out checks discharge thermistor a few k ohms out so decided to ring back and spoke to someone else who this time told me discharge sensors are all 10 x a normal resistance reading and to disregard what i originally got told. left me very confused so i asked him to ask his collegues whilst i was on the phone and he said its in blue and white mate ie black and white lol but the app is blue and white.

if the above is true then the discharge thermistor is miles out had original reading of say 50 deg c at 5.26k ohms and at 24 deg c when i removed thermistor off the pipe and clamped temp sensor straight on to it it read 19.40 k ohms if the second guy is to be correct it should read around 208 k ohms.

So to be sure i have reclaimed and verified the charge which is correct so it may be the thermistor is out. causing this situation. i have checked all the other thermistors air/coil these are fine.

1. so is this correct then are all discharge thermistors a higher resistance?
2. If so is this the same for most kit ie, mitsi toshiba sanyo fujitsu etc.
3. could there be anything else causing this fault of shortage of refigerant.

thank you

[install monkey]

had it on a 4mx system and it was dirt within the condenser, but the face of it was clean, worth a try if ur thermistors appear ok
http://www.mediafire.com/view/?ht2mf9ybxhe4wn6

[moondawn]

hi install will give that a try, the thing with the discharge thermistor is if i believe the first guy it would be a couple of k ohms out maing around 8-9 deg c diff to what it should be. if i believe the second guy then the sensor is miles out.

cheers

[install monkey]

trawled through that manual and usually if the discharge sensor is different from the rest then theres a graph with the resistances, so i would assume theyre the same values

[moondawn]

hi install do you use the daikin app? because discharge sensor is 10 x difference than the air and coil sensors basically because the Discharge thermistor gets a lot hotter

[install monkey]

use doctor daikin

[install monkey]

and daikin text fault codes

[moondawn]

ahh right well cheers for your input mate will blow through the coil tommorrow.

[install monkey]

also check suction pressure transducer as if it thinks its sog then it will slow compressor down- from memnory its 3 wire -red,blk,white- accross 2 will be 24vac signal output- will be about 5v dc (to earth or neutral)

[moondawn]

been back on site today, recommisioned system and odviously getting the same symptons as before seems like low pressure is high and high pressure is low. so as i struggled to get some of the charge in because low side is too high i decided to pump the system down in forced operation would only achieve 4-5 bar on pumpdown before compressor going off and pressure equalised. later on i did get around 3 bar but again pump down did not work. checked amps and mainly compressor ran around 5 amps sometimes peaking to 8 amps but not much change in high pressure side which was hp liquid port on cooling.
Also seen on the service led monitor outside that it had faulted on relay overcurrent or high discharge temp again suggesting that thermistor could be faulty. i was measuring discharge line and it never went above 82 deg c.
I have listened to EEvs on start up they are making a noise suggesting working i have also switched system to heat mode which will open eev then i have powered down and removed eev heads then restarted in cooling but to no avail.
this is a basic system really no lp switch or transducer. so hoping its the discharge thermistor however maybe compressor is inefficeient.

what u guys think?

[Darrenp]

Had u0 on daikin split , it was expansion valve body , got new head and body .. Never had the prob again

[moondawn]

Had u0 on daikin split , it was expansion valve body , got new head and body .. Never had the prob again

hi darren how did you find out which eev body and head was faulty?

[install monkey]

you can swap the heads quite quickly by lifting them off and swapping plugs on the board, but its always the body thats at fault- usually found by poor output of an indoor

[moondawn]

Update regarding this post turned out to be a bad compressor. compressor now changed and fully working.

[Darrenp]

Had this problem before .. EXPANSION VALVE