View Full Version : Mitsu

11-10-2002, 09:03 PM
I have a 10 year old Mitshubishi Heat pump displaying error code P6 on the controller. I have misplaced my Mitsu technical manual. Would anyone care to advise me what this error code is. Thank you

Its the PUH series I think

13-10-2002, 11:07 AM
yeeeeee.p6 refers to coil frost/overheat protection.activated when indoor coil temp has been below -15 or over 70c for more than 2mins.check that the system has the correct gas charge .And what pressure its running at.If not thermistor resistance. Are the air filters and indoor coil clean.Does the indoor fan run ok.hope this helps yeeeeeee.:)

13-10-2002, 11:44 AM

Thanks for your help. I think I know, its the filter on the indoor unit, its clogged up. Normally the customer is responsible for cleaning them, few months back I was relocating the outdoor units and noticed the dirty filters so cleaned two of them. I didnt clean this one as it was upstairs. Im pretty certain thats what it is. These Mitsus have been running now over 10 years without a problem. Im now putting in 6 LG's on a new section. Hope there as good as the Mitsubishi. If the filter clean doesnt sort the problem I will have to check the gas charge. System had a leak and was refilled with R22. Lets hope the filter clean sorts the prob out

13-10-2002, 06:04 PM
Hey Mark,

Hows it ex ay, I was wondering where you got to
Anyway nice to see youre still with us on mother earth!!
I will give you a call this week and we can meet up. Tomorrow , Monday Ive got a major dental appointment, bridges and crowns and all sorts, thats the result of eating too many Beacon sweets

Look forward to speaking soon

03-01-2003, 10:19 PM
This time showing error code P8
I cant find my manuals
Would anyone know??

Thanks in advance

04-01-2003, 01:42 PM
Hi Aiyub

Error code P8 refers to a high pressure fault on the outdoor unit - this is more often than not caused by dirty indoor air filters causing the head pressure to exceed 400psig ( the cut out setpoint) during heating operation.


04-01-2003, 05:32 PM

Ive cleaned the filters. Unit will still not come on. How do I reset the HP control. All the LED's are lit except for LE8 which according to the wiring diagram is the cranckase heater.

I can hear a noise, I think coming from the relay switch, it comes on, murmers for a while then cuts out. Repeats every now and then.

Power to units is fine.

Its a PUH 2.5 Mr Slim model Cassette system. Im going again tomorrow morning, see if I can do something to get her going.

04-01-2003, 07:40 PM
Hi, Aiyub:)
from memory the reset is either by pushing a button inside a hole on the wall mount control or by powering down and up again. I could be wrong as it is a long time from I worked on a split, but until someone how knows posts you may try that.
Regards .Andy:confused:

04-01-2003, 09:06 PM
Aiyub its a long time since i worked on a Misti Slim but i recollect that P8 has a couple of fault meanings. One of them is HP but another could be a faulty thermistor. Have you checked all thermistor resistance readings to their corresponding temperatures? Is the power supply 3 phase and is the phase rotation correct. Is the pcb faulty and not resetting itself when you push the clear memory button on it?
Just a few points, hope it helps.

04-01-2003, 09:11 PM
Hi Aiyub,

Is it a 3phase condensing unit?If so p8 can refer to phase imbalance or rotation direction, try swapping two phases.Inside of condensing unit cover should detail led faults, are any flashing?Could also be loss of charge or faulty boards



05-01-2003, 12:13 PM
Unit is single phase. I have reset SW1 and SW2 on the pcb board which flushes out the memory and resets the controller. Im going to site just now, will take all the readings.

I got a feeling pcb board is faulty. Im dreading this one, and its Sunday and all.

Will post again tonight and tell you how I got on. Just one thing, I installed these air conditioners 11 years ago, I remember I purchased them from Bison Air Conditioning in Nottingham, from Stan ( Are you still out there?? ) I had all the manuals stored in a bankers box accumulating dust, then I had my house move, and I think I binned the lot. What an awful mistake.

Moral, Never, ever throw away anything containing technical information. I went to the Mitsu site on the internet, No info on the Mr Slim PUH series , this one is a PUH 2.5 I think. Maybe units are too old to qualify for technical help.

05-01-2003, 02:19 PM

if you private message me an e-mail address I'll send you the Mitsi fault codes.

If you have all the led's lit except no.8 then the unit should be running. From memory - as I'm not in the office - I think the led's are as follows:
1 - indoor unit running
2 - demand from the indoor unit
3 - contactor on
4 - compressor on
5 - coil sensor open circuit or short circuit
6 - reversing valve energised
7 -
8 - crankcase heater on

sorry, can't remember no.7.

You can reset the hp by powering down and then back on but before you do look at the led's for the one flashing which will give you the fault. When you power down you wipe the memory so the fault code disappears. Remember to power down the indoor unit as well as these are on a different circuit and you need to do this to clear the fault code on the controller.

If the contactor and compressor led's are lit on the outdoor unit then you should look carefully at the compressor - does it have voltage to it? if so then the klixon may be open circuit and you have possibly got damage to the pot from overheating.