Fault on a Hitatchi split unit.

[marc5180]

Got called to a unit today and the indoor coil had frozen up and was dripping water. I looked a little closer and when i turned off the wall controller the indoor fan went off but it sounded like there was gas still going through the coil after 10 mins.
I went upstairs to the condensor and sure enough the compressor and condensor fan was still running even though the controller was off.
I couldn't get the model number of the condensor as it had worn off but the indoor was a Hitatchi RCI-3AQ1 with a code of U4D01702 it's on R22 and is single phase. I rang hitatchi but they didnt have any wiring diagrams for it because it's such an old system.
For the compressor to stay on when the controller was off made me think that either the contactor had stuck in but it hadn't. I then looked if the compressor had somehow got a permenant live to it- which it hadn't. I looked for the interconnecting cable but i couldn't find it ( i know that sounds silly) but the only cable i could see went to a relay near the outdoor PCB, im lost and without wiring diagrams im going to struggle can anyone suggest anything to try or send me a link to the manual please?

[The Viking]

the only cable i could see went to a relay near the outdoor PCB,

You did check that the relay wasn't stuck, didn't you?

Normally when these things happens there is a stuck (or "welded") relay somewhere.
On indoor PCB or near indoor PCB are the classical places....

[marc5180]

I gave it a slight tap with the screw driver to check it wasn't stuck.
I havent seen an interconnector going to a relay before they just normally go to the terminals on the board. How do a check if a relay is tuck?

[nike123]

I looked for the interconnecting cable but i couldn't find it ( i know that sounds silly) but the only cable i could see went to a relay near the outdoor PCB, im lost and without wiring diagrams im going to struggle can anyone suggest anything to try or send me a link to the manual please?

You say that "only cable i could see went to a relay near the outdoor PCB".
1. Does that mean that outdoor unit have its own PCB?
2. Does outdoor unit have power supply cable and communication cable toward indoor unit
3. When you say "relay near the outdoor PCB", did you mean that relay is in the outdoor unit body and near the PCB

If all is Yes, then it could be that relay contacts are welded or, PCB relay output is active because of outdoor controller IC fault.
You could check that by disconnecting connector (two thin wires) of control circuit of relay during operation of unit. If after that compressor stop, then it is faulty outdoor unit PCB and if not, then it is welded relay contacts.

[frank]

I gave it a slight tap with the screw driver to check it wasn't stuck.
I havent seen an interconnector going to a relay before they just normally go to the terminals on the board. How do a check if a relay is tuck?

Using your meter - check first if there is any voltage going to the A1/A2 terminals (the coil)
Then check to see if you have voltage on the input side and output side. If you do not have any voltage to the coil but you have voltage on the 'output' side then it is stuck in.

[marc5180]

Thanks guys, knew i could rely on you

[Chill doctor]

Do you have a model number?

[nike123]

Try read original post again!

[omurcelik]

hi there ... first of all open that url..http://www.hitachiaircon.com/technical/manuals.jsp
than select utopia ;afterwards select (utopia hp-r22_tcgb0004.pdf) i suppose thats what u want 172 pages service manual if u cant open that u register the site than site allows u see the manuals

[omurcelik]

as far as i see from the manual (ms) out used for compressor;contactor is double poled and thats why u may measure wrong contact

[Chill doctor]

Ok series ones used to send a 240 volt feed down a single wire interconnecting, this was the feed that runs through the hp, overload and other mechanical safeties before finally feeding the contractor coil to feed the compressor, so,,, either your contractor is stuck in, (does contractor still remain closed when power off) or the pcb relay is welded shut, try disconnecting the interconnecting cable, if compressor runs its the contractor, if not its the indoor pcb, save any faulty wiring,

PS the wiring diagram should be on a sticker in the out door unit unless its rubbed off.

The way this sytem works is: indoor unit calls for cooling, the pcb supplies power (240v) to the interconnecting wire (there is only one used) the indoor pcb then measures the current that wire pulls, it expects a small amount of current to be pulled from the coil on the compressor contactor. if it does not measure a small current draw it shuts the power down and alarms 02 alarm.

PS this unit is 18 years plus old so there is a strong likelyhood someone has altered wiring.

Chill doctor

[marc5180]

Ok series ones used to send a 240 volt feed down a single wire interconnecting, this was the feed that runs through the hp, overload and other mechanical safeties before finally feeding the contractor coil to feed the compressor, so,,, either your contractor is stuck in, (does contractor still remain closed when power off) or the pcb relay is welded shut, try disconnecting the interconnecting cable, if compressor runs its the contractor, if not its the indoor pcb, save any faulty wiring,

PS the wiring diagram should be on a sticker in the out door unit unless its rubbed off.

The way this sytem works is: indoor unit calls for cooling, the pcb supplies power (240v) to the interconnecting wire (there is only one used) the indoor pcb then measures the current that wire pulls, it expects a small amount of current to be pulled from the coil on the compressor contactor. if it does not measure a small current draw it shuts the power down and alarms 02 alarm.

PS this unit is 18 years plus old so there is a strong likelyhood someone has altered wiring.

Chill doctor

Hi Chilldoctor you were right....i went back to the unit yesterday and after going through all of the electrics i finally figured it out ( before i read your post). I started from the compressor and worked backwards, checking boards, relays , contactors, fan pressure switches, fan etc. After checking through evertything the only thing left giving 240 v when the indoor unit was off was a blue wire, which i figured out was the signal wire.I traced this downstairs and found 240v coming off the indoor board when there should be no voltage. So i have ordered a new board but been told to expect to with up to 12 weeks whilst they source the part from Japan.
I started checking for the fault back to front i shouldn't have started from the compressor but from the indoor unit, it would only have taken me half an hour to suss out what the problem was...but i'll know better next time.