Please Help Mitsubishi Heavy Ind problem

[simplycooling]

Hi people,
Im new to this forum but was wondering if anybody could shine some light on a problem im having on a piece of equipment ive just finished installing, Its a 250 series outside condenser, 3 phase two fan condenser, supplying two 125 series cassettes, (twin split) i commisioned the system a couple of days ago and it was running in heating correctly,(about a hour and a half) i was then called out by the customer that it had tripped the MCB (C20 3 phase MCB) 60 amp, i reset everything then tried to run it up in heating and it went out on HP, even though it was running fine a few hours before, i thought it might be down to a blockage(moisture) so i reclaimed the Gas, cracked the liquid flare and purged through with nitrogen, vac'ced the system to 2 torr and recharged with fresh virgin refrigerant, started unit up and it ran fine for about a hour, i have just been contacted by the customer and apparently it has tripped the mcb again, Any ideas on what could be causing a HP problem on a newly installed system and how it could be tripping the MCB even though its going out on HP. When it was running fine it was running about 35 Bar running hard in heating, any opinions or surgestions appreciated,
steve

[Gary]

Telling us the pressure doesn't do much good if you don't tell us which refrigerant you are using.

[nike123]

What is full model# of outdoor and indoors?
Is it outdoor FDC 250VS
and indoors FDT 125V

[nike123]

telling us the pressure doesn't do much good if you don't tell us which refrigerant you are using.

r410.......

[Gary]

That would put the SCT at about 135F/57C. Either it isn't getting enough airflow through the indoor coil or the system is grossly overcharged.

We need to know the temps of the air entering and leaving the coil as well as the liquid line temp.

[nike123]

This should be refrigerant diagram if model numbers match those I presumed.

[Thermatech]

In heating the system will have traget HP about 30 bar with R410a.
But if the pressure sensor is reading 10 bar too low at 20 bar the outdoor circuit board will make compressor run at max speed because target HP not reached.
then
outdoor unit runs to 41 bar & trips on HP safety switch although HP sensor still provides 30 bar data to circuit board.

In this case indoor units ramp down LEV valves to reduce refrigerant flow as set temp is achieved in the rooms but outdoor unit still runs comp at max as HP sensor data is incorrect.

Suggest use service manual to trouble shoot HP sensor & make sure it is reading correct pressure.

[nike123]

High pressure switch should act at 41,5 bar and close at 31,5 bar so first check his proper functioning.

[simplycooling]

Hi thanks for the replys, so far, what a brillaint forum, yes it is a FDC250VS and 125 cassettes, Its running on 410a, I reclaimed and re commisioned system this morning to factory weights, anybody have any idea why it would be tripping the MCB indoors aswell as activating the HP switch, I suspect a faulty HP switch, anybody experienced faulty MHI parts in new equipment, steve

[GHAZ]

hi simplycooling i had a problem on a chiller years back with mcb tripping and what it was C rated mcb trip when it should of had a D mcb RATED TRIP

[BritCit_Juve]

The higher the pressure the compressor has to work against then the ampage drawn is raised as well. However as these units should only need a breaker rated at 32A they should not be tripping a 60A mcb.
I think the first thing I would do is fit some Gauges and see how high the pressure goes.
At the same time check that all the solenoid actuators are firmly afixed to the valve and to the pcb.
I dont think the MCB trip problem is related to this but I would contact Chris at HRP ougham as he will probably have a recommendation.
Brit

[BritCit_Juve]

Sorry thats Rougham lol

Good call Ghaz but as the system is inverter based it should only draw 5A on start up so a Type D shouldnt be required.
Brit

[GHAZ]

i forgot to write type c mcb is 5 to 10 times surge and type d mcb is 10 to 50 times surge

[coolhandlew]

C curve mcb will not trip under normal circumstances. Especially 60A!!!! I would expect 32A type C ample for this unit. Look for other problem.

[coolhandlew]

I read the original post again. C20 3 pole 60A. Is it not a 20A mcb?

[nike123]

Presumable cause

1. Short circuit of air flow, disturbance of air flow and clogging filter at heat exchanger (Condenser side)/Breakdown of fan motor
2. Defective outdoor control PCB
3. Defective 63H-1 connector
4. Defective electronic expansion valve connector
5. Closed service valve
6. Mixing of non-condensing gas (nitrogen, etc.)

[Daikin=Overated]

Re. Nike123..........Mixing of non-condensing gas (nitrogen, etc.)

I think this could still be the culprit. When you reclaimed the charge in the system did you ensure that the solenoid valves were energised. I.e power to the system whilst vac'ing??

I've had this so many times that on certain systems (especially Daikin) depending on the design, that it's possible to retain trapped nitrogen/refrigerent from the previous charge or whatever in a closed circuit being held off by a solenoid valve in the condenser.

My advice would be to have a look at the diagram, cross-ref with the Tech guys at Slough or wherever and determin whether this is a possibility or not?

In this sort of climate you obviously shouldn't be going out on HP unless theres a servere air restriction to the indoor unit. On this note, check the indoor fan. Watch it for the hour the system allegedly trips-see if somethings shutting down whilst the compressors still pumping. It could also be that the contactor or pcb is holding in when the systems reached temperature-i've had this too!! The system should still go out on HP mind and not blow the breaker, however if the amperage being drawn is in excess of the rated MCB prior to reaching the limit HP then it will blow it regardless.

When you confirm the readings on the gauges as Britvit above menitoned already, check for signs of non-condensibles. If so then that's how these non-condensibles are remaining in the system regardless of how many times you reclaim, vac, recharge.

Hope this makes sense.

Regards,

J.

[nike123]

Re. Nike123..........Mixing of non-condensing gas (nitrogen, etc.)

I think this could still be the culprit. When you reclaimed the charge in the system did you ensure that the solenoid valves were energised. I.e power to the system whilst vac'ing??

From refrigerant diagram is obvious that there is no valves in indoor units, so non-condensables could not remain in system if evacuation is done properly.

[Daikin=Overated]

From refrigerant diagram is obvious that there is no valves in indoor units, so non-condensables could not remain in system if evacuation is done properly.

No. you've misunderstood

I'm refering to the outdoor (CCU) unit solenoid valves where theres usually two or more-the 4 way valve solenoid for one!

I'm not suggesting theres valves on the indoor. I haven't said anything of the sort sorry.

J.

[Daikin=Overated]

Re. Nike123..........Mixing of non-condensing gas (nitrogen, etc.)

I think this could still be the culprit. When you reclaimed the charge in the system did you ensure that the solenoid valves were energised. I.e power to the system whilst vac'ing??

I've had this so many times that on certain systems (especially Daikin) depending on the design, that it's possible to retain trapped nitrogen/refrigerent from the previous charge or whatever in a closed circuit being held off by a solenoid valve in the condenser.

My advice would be to have a look at the diagram, cross-ref with the Tech guys at Slough or wherever and determin whether this is a possibility or not?

In this sort of climate you obviously shouldn't be going out on HP unless theres a servere air restriction to the indoor unit. On this note, check the indoor fan. Watch it for the hour the system allegedly trips-see if somethings shutting down whilst the compressors still pumping. It could also be that the contactor or pcb is holding in when the systems reached temperature-i've had this too!! The system should still go out on HP mind and not blow the breaker, however if the amperage being drawn is in excess of the rated MCB prior to reaching the limit HP then it will blow it regardless.

When you confirm the readings on the gauges as Britvit above menitoned already, check for signs of non-condensibles. If so then that's how these non-condensibles are remaining in the system regardless of how many times you reclaim, vac, recharge.

Hope this makes sense.

Regards,

J.

I do believe I stated valves in the condenser!

{depending on the design, that it's possible to retain trapped nitrogen/refrigerent from the previous charge or whatever in a closed circuit being held off by a solenoid valve in the condenser }

Ta.

J

[nike123]

No. you've misunderstood

Most probably!

[Daikin=Overated]

Nike......I Hope you don't think I was throwing the toys out the pram, it's all constructive criticism which could ultimately help toward resolving the fault.

I have since checked back over the diagram you listed- the outdoor schematic seems very straight forward. It doesn't mention the solenoid on the four way valve for example, although obviously we all know there's going to be one on there. Could there be another on the head pressure side of things?? You'd hope they'd say so-but as it's not listed??

Regards,

J.

[nike123]

Nike......I Hope you don't think I was throwing the toys out the pram, it's all constructive criticism which could ultimately help toward resolving the fault.

No, I am not, I really think that I misunderstood your last post.

I have since checked back over the diagram you listed- the outdoor schematic seems very straight forward. It doesn't mention the solenoid on the four way valve for example, although obviously we all know there's going to be one on there. Could there be another on the head pressure side of things?? You'd hope they'd say so-but as it's not listed??

Regards,

J.

From my memory, there is no solenoid valves other than 4-way valve.
I don't see what additional valve would be used for in this particular AC unit.

[Daikin=Overated]

So what's the latest Simply Cooling??