mr slim problem

[philjd26]

hi
strange problem with a 2 too 1, model number-( puh -6yksa) indoor (plh-3kb)

sequence of events

start test mode in cooling
unit runs for about 8 minutes
trips on a p8 fault or sometimes the controller goes dead.
start test mode in heat and the coil temp seeems low @ 10c, however temp air discharge is good.

i have confirmed that all safetys on the outdoor are ok, all sensors are within range both indoor and out.
i have tried change outdoor pcb, with no luck.
i confirmed interconnecting cable is ok.

any ideas gents??

[Grizzly]

Hi Phil.

Check out these fault codes, (Just in case you do not have them?)
I hope they are of assistance?
Cheers Grizzly.

Also check out the 2nd doc.

[nike123]

Check refrigerant charge by recovering and weighing. Also check refrigerant composition with PT-chart while refrigerant is in recovery cylinder and temperature of cylinder (and refrigerant in it) is equalized with ambient. You need empty and vacuumed cylinder for that.

[Thermatech]

On the old K series the indoor unit cannot directly communicate any data between indoor unit & outdoor unit.
The only way the indoor unit can judge if the outdoor unit is working is by monitor of indoor coil temp sensor.
So if indoor unit set to heating mode & indoor sends 12vdc command to outdoor unit to run comp & energise 4WRV for heating
then
Indoor unit starts to monitor indoor refrigerant coil temp.
If the sensor does not show hot gas temp rising within a short period of time the indoor unit consders that the outdoor unit has some sort of problem & shuts down on P8.

So make sure indoor coil temp sensor is showing hot gas temp in heating with the remote controller coil temp code
Code 10 = +50 degC

Suggest replace both indoor coil temp sensors as precaution as these are relatively cheap.
If system still stops on P8 then consider changing indoor circuit boards.

I wonder why the remote controller goes dead ?
That might indicate some power supply problem to indoor unit circuit board or intermittent transformer problem or circuit board problem as remote controller gets 12vdc from indoor circuit board / transformer.

[philjd26]

Thanks for replies

Therm I got something off the web that suggests if there is a low delta between coil temp and r/a temp it goes into frost protection giving a p8 alarm!!
The cassettes are positioned badly, one is up tight against a wall and the other is in a smallish area with a low ceiling, I am wondering if short cycling is happening!!

Also the slave unit that just has a connection to controller does this unit have ability to shut down outdoor ??

[Thermatech]

My uderstading from memory & service manual
Cooling mode
P8 after 8 mins if coil temp is less than 5 deg C diff between return air temp & coil temp.
Indoor unit considers more than 5 degC diff ok.

Coil frost prevention
when coil temp is minus 15 deg C or lower for 3 mins compressor is stop for 6 mins
then
if still -15 or lower after further 10 mins of compressor operation stop on P8.

K series R22 units

[philjd26]

Thanks therm
As you say 8 mins it is very close to the actual time it takes to alarm I did hold the return sensor and unit ran for 15 mins no problem..
However the shut down of the controller and the fact I had it in test which I thought overrides the r/a sensor is a bit strange!!

I think il reposition return sensor..

Thanks therm