mitsibishi vrf fault

[airconadam]

hey fellas long time since ihave posted on here but here it goes. Went to a unit the other day its a vrf mitsi with 7 indoor units on it and was faulting 1102 (high discharge temp) so i thought ok spoke to mitsi and he said you possibly got a leak told him pressure's which were slightly low etc etc. So plan was to remove gas,pressure test,find leak etc etc but then as we were leaving site ready to go back on monday coming it faulted 1500 (overcharged) now this unit is only 12 months old and has run fine untill now so on the way home i spoke to mitsi again and he said that could be why your getting the 1102 fault (high discharge temp) but i was thinking on the way home after i put the phone down why all of a sudden? a leak maybe, but overcharged?? any one got any ideas and why you think maybe this has happend thanks alot

adam

p.s Its on R410A

[Thermatech]

What model City Multi ?

1102 fault is classic short of gas fault but is just discharge temp sensor showing excessive discharge temperature at 120 deg C or more which can be caused by a failed valve anyplace in the system which will make low suction pressure & then cause high discharge temp the same as SOG.
If you look in service manual you will see 1102 fault covers a multitude of sins, but SOG is listed as first possible cause & followed by a list of further 14 other possible problems mainly solenoid valves & LEV valves not opening.
So its best not to assume SOG & go through the recover the refrigerant procedure untill you are sure that this is the actual cause of the 1102 fault.

The 1500 fault is interesting because it will only flag this fault if the discharge super heat is less than 10 deg C.
So how can the system see excessive discharge temp & then very low discharge SH on the same day ?
Something else has to be causing the conflicting faults.
The discharge temp sensor is common to both faults & is often the first sensor to fail because it is subjected to the highest temperature & temp change in the system.Sometimes the sensor gives intermittent incorrect data reading to the control board as it starts to fail but before it completely fails open or closed circuit.
So I would look very carefully at this sensor & the data using SW1 on the control board.
If the discharge temp sensor is ok then monitor the system to look for LEV valve & solenoid valve operation at B/C box & indoor units.
For instance,,,,,,,,,, assume one indoor unit LEV valve is locked open & unit is switched off.
The liquid line is alway live & so the indoor unit coil fills up with liquid when the unit is off & gas solenoid valves at B/C are shut. In this case the gas pipe from the indoor unit all the way back to the B/C also fills with liquid. On a large indoor unit with 30m pipe lengh from B/C this could be a large volume of refrigerant which has become trapped & has the effect of making the outdoor unit look SOG.
Now assume the indoor unit is switched on in cooling mode. Suddenly all that trapped liquid gets dumped into suction & rushes back to the outdoor unit.

I would normally identify this type of problem within an hour or two but I have the help of the M-net monitor tool lap top computer.
You can find the cause with a service manual & a bit more time. But you have to be prepaired to look at the whole system & test in heating & cooling modes to locate the one valve which has failed.

[airconadam]

excellent thermatech the model num i cant quite remember think its a purfy-300 all the units on this system would not cool or heat,ihave tested thos sensors before on other syetems were you can alter the dip switches as you say and it gives you the pressure on low/high side and match with your gauges etc thanks for all the information

adam

[PRESS]

Air con Adam

You did not tell whether you really found the leak which you were looking for though. I met a situation like that before. It is highly unlikely that you could be having a gas leak in actual fact you should lose head instead when you have a gas leak. The following is what i suggest you look out for.

Check whether your condenser is clean. Do not be fooled by the nice aluminium clean look the condenser fins give you they accumulate dirt inside. Give the condenser a thorough wash. Believe me it really works. It does matter that the unit is still 6 months old maybe its location subjects it to dirt accumulation seriously.

If it is clean check if the condenser location does not deprive it of adequate air circulation. Also check if there are no sources of heat in the visinity of the condensing unit.

[airconadam]

no i never found found any leak on any flare nuts condensor is tottaly clean and in a well ventilated area also got problems with access aswell to inddor units so some areas are difficult, think i will give mitsi a ring again and see what they suggest as they must have more problems like this all the time.
thanks alot

adam

[The Viking]

Adam,
I would listen to the advice given by Thermatech to start with.

BTW, why not just get Mitsu to site? The units should still be under warranty....

[PRESS]

Hi

If you manage to get Mitsi to site keep us posted with their technical view on this thread please.

[airconadam]

yer exaclty what i said to my boss but he wants us to do it for some reason must be for money issues. yer iwill keep you guys posted on what i find tommorrow thanks guys

adam

[The Viking]

Press,
I would listen to any advice given by Thermatech to start with.

[PRESS]

viking

Thermatec's advice is very good though but involving the original manufacturer in such cases where mysterious problems occur excellent for the reason that we want them to see their flaws and cover our backs

[Thermatech]

Many thanks to Viking for a vote of confidence!

Unfortunately at this time of year most employies working at corporation companies are busy using up the 2007 holiday allowance because it a 'use it or loose it situation'.
Last week a contractor was quoted 3 weeks for a site visit from a major manufacturer.
You will need to be the most important contractor in the uk to get a site visit from most manufacturers now before Xmas. Other wise wait your turn & get a visit to site in January.
Most enusers will not accept that sort of delay when they depend on the a/c system for all heating & cooling in the building & will therfore demand that the contractor resoves the problem or the maintenance contract will be terminated.
So Adam needs to sort this out for the customer asap.
Technical
When the outdoor unit has 115 deg C on discharge temp sensor it reduces compressor speed to protect compressor from overheat.
That is why all indoor units have poor or no performance because the outdoor unit reduces compressor speed untill it is only at minimum speed & then if at min speed the discharge temp still rises up to 120 deg C the outdoor unit stops.
If then the outdoor unit gets to discharge temp of 120 deg C within 30 mins the outdoor unit stops again.
When the outdoor unit has repeated this process 3 times,,, then it stops & reports a 1102 fault.
If you look in the fault code history using SW1 dips you will find lots of 1202 ( preliminary discharge abnormality). If the system has a G50 central controller you will see the preliminary fault codes recorded when you go into the 'engineers mode'.
When the fault record is 1102 & 1202 faults then SOG has to be the prime suspect.
But because in this case the system also reports a conflicting 1500 overcharge fault then there must be another problem which needs to be investigated first before removing all the refrigerant. If Adam spends a day removing the refrigerant & then finds the refrigerant charge to be correct then he is in a difficult possition with the customer.

[airconadam]

yes i tottaly agree thermatech if only i knew the correct charge aswell as nothin has been labelled up etc all i know is the standing charge that the unit came with but with have a good luck tommorrow thanks again

adam

[Contactor]

Faulty thermistor and / or board?

[airconadam]

hey fellas went back to the system today and as i walked into the building iwas grreted by a woman saying thank you for fixing the air con so then alarm bells was ringing when i went into the rooms they were all freezing and people had turned them off so i rang mitsi up and told them everything fault codes etc he also said that if i only had 1 or 2 units running after 20 mins it would fault due to the condensor being so big and not being able to due its job correctly there has to be more than 30% duty to run correctly. So he suggested that we reclaimed the refrigerant and all thos codes and problems point to it being the ref charge (no mention of valves etc which i mentioned to him) iwas unable to find the exact charge of the system so i didnt really want to touch the system just yet just want to see what you veiws are thanks alot fellas.

adam

P.S thanks for your pm thermatech much appreciated

[Thermatech]

Confirmation of exact refrigerant charge can be a good place to start as it is very often the cause of many problems.
You will need to recover all the refrigerant & while your recovery rigs is doing its stuff you will need to do a complete survey of the installed refrigerant pipework. Then you can calculate the trim charge & add that to the outdoor unit charge to end up with a total system charge. Ideally the installing contractor would have completed commissioning sheets & included them in the O&M manual which the enduser should have a copy. So its worth asking them to make sure.

Did you check the TH11 discharge temp sensor ?

I just hope you dont spend a day removing all the refrigerant only to find it had the correct charge anyway.

Tip With the cold weather remove back panel of outdoor unit & use two 3kw fan heaters to make the suction accumulator as warm as possible other wise the liquid will sit in the accumulator & it will take forever to get it out. Also keep power on to the outdoor unit to keep crankcase heater on to boil off any refrigerant in the compressor oil.
You can disconnect communication cable to make sure no one switches on any indoor unit because you dont want the compressor to run while your recovering, or otherwise you can unplug the pressure switch or pressure sensor to make the unit stay off on a pressure fault which will do the same job.
Make sure to recover from both high & low side.

There is a chance that the system has a fault which has made it look SOG & some one may have added refrigerant in an effort to overcome this problem but now the system is actually overcharged & this could be why you have intermittent 1500 overcharge fault.
So at the end of the day confermation of the actual total system charge is usefull.

But think about the high discharge temp 1102 fault. If the system was overcharged & the SH is therefore less than 10 deg C then the compressors more or less starting to pump liquid. How can the system go from this extreem operating condition to the other extreem operating condtion of excessive high discharge temp which will only happen if the suction pressure is very low & the SH will be very high.
This will never happen in a system which has correct operation.
The outdoor unit is either getting incorrect data or the or the refrigerant pressures & temperatures are actually going to these extreems & to resolve you need to find out why.

PS why do you think the rooms were so cold today ?

[airconadam]

exaclty what i was trying to find out today thermatech about the commisioning sheets considering the building is only 8 months old i was unable to find any out of the 11 manuals so iam still trying to hunt them down. There is no possible way i can trace the pipework due to no access and everywere plasterboarded up. Inever checked any thermistors. Also i have not got a clue why it started to cool and heat just as it should and worked all day with no problems thanks alot for the help and iwill post back asap

adam

[The Viking]

Adam,

It can be difficult when the pipework is hidden, but generally, if you take an educated guess as to where they are and measure the length, then you will not be far of the mark (even if you are a couple of meters out, it won't make much of a difference and it will be better than not having a clue at all). The pipe sizes can be seen at each end.

Another good source of information is the "as installed" drawings (but be careful with these as more often than not they are not exactly as installed).

Another BTW,
What happened to the original installer?
If the customer fell out with them, did they commission the units properly?
If the customer didn't fall out with them it might be worth giving them a call.

[Zaff]

Hi adam
Have you tried running the indoor units up individually to prove the BC port connections. Some of the units may have been addressed incorrectly on the indoor board SW14. Indoor may be asking for cooling but the BC port may be trying to heat. This could cause problems in the BC resulting in flood back -1500 or high superheat -1102.
Tracing the pipework is the easiest way to confirm.

[Peter_1]

Units all running now in heating mode, are the indoor coils not all too much clogged so that you have not enough condenser capacity?

[Thermatech]

If the enduser tells you that the commissioning sheets were never issued because the installing contractor went bust ,,,,,,,,,,, dont believe them.
I would like a pint of beer for every time I have been told that one.
If you dig a bit deeper you often find that the installing contractor was never fully paid & so the enduser has been left with no warrantee & is forced to use another contractor to resolve any problems which the installing contractor would have sorted out during the warrantee period.
This type of enduser is often the worst type of late or no payment offender.

[Peter_1]

Thermatech, I agree 100%

[airconadam]

hey fellas iknow who installed it but they sent a commisioning sheet with temps etc of the indoors,but who knows they could of easily made them up. I think iam going to give them a ring and ask them myself. So far the unit is still running and not had any problems with it as of yet will keep you posted thanks alot

adam

[sinewave]

Adam


If you & the customer are still in contact with the 'instaler' and the system is ony 8 months old why aren't they sorting this?


Mitsi don't take kindly to peeps instaling their kit and legging it with a guarantee that lasts as long as the cheque takes to clear!

[airconadam]

hey fellas long time ago this post now,but just an update ended up getting another over charge fault and ended up speaking to mitsi again and was asked to check the LEV's from the outdoor unit.If i remember correctly put them on cooling then we worked out which ones were open etc and one of them was not! when checking all the boards etc we found an LEV had come loose and was disconnected!!! as you said thermatech in your first post! thanks alot

adam

[Thermatech]

Had one like that again a few weeks ago.

Lev plug on the indoor control board can easily get dis lodged when installation engineer makes power & contol wiring terminal connections.

So many things can cause the over charge / under charge faults but the main thing is you sorted it & have much better understanding of what to look for next time.

Thanks for your feed back

[airconadam]

yes another one for the memory bank thanks alot thermatech (again)

adam

[kevingrange]

I have had problems with this 1102 fault and have found best to check the hp gauge reading with the hp sensor reading on SW4. If you find the sensor is faulty and needs replacing then Mitsi make a replacement kit which fits in seconds and eliminates the need to reclaim and braze in a new part. I have also had this fault with an ev fault on an indoor unit jammed shut. I have generally found that if the standing pressure/temp is correct then the system will run and not fault out even if the system is sog.