Mitsubishi Mr Slim R22 split system

[BigDeal]

I need help on a Mr Slim split ductless system ...Indoor model number MS-a3ond outdoor model number MS-A3OND ...Evapourator comes on runs for about 3 minutes then the operation light just blinks over and over ...Condenser never comes on ...replaced both circuit boards with boards from another system that works ....did the same thing ...according to the service manual this indicates mis-wiring between indoor and outdoor unit ...checked the wiring and it is fine ...have no idea what else to check ....there is power to the outdoor unit and 5 volts on the board at the test point ...any ideas?

[Royal241]

take it appert and start your wiring all over again. I did that when comming across some units installed by other people that never worked. take your time and don't give up, never know who was there before you.

[Thermatech]

Mr Slim system
The model numbers are different from R22 units supplied in the UK.
Here R22 Mr Slim units were K control type.
Outdoor unit & indoor unit had seperate power supply.
Interconnecting cable was 3 core 12v dc.
Indoor unit sends command to outdoor unit with 12v dc.
12v dc between terminal 1 & 2 = compressor on (cooling)
12v dc between 1 & 3 = reversing valve energized for heating mode.

If the interconnecting cable is disconnected then indoor unit sends 12v dc command but outdoor unit does not operate.
In this case indoor unit is monitoring indoor refrigerant / heat exchanger temp & when no change indoor unit stops on P8 fault.

Also any other protective divice activation at outdoor unit will result in P8 fault & LED flash on outdoor board will indicate the type of fault.

M series system
But if the unit is M series then outdoor unit gets 240v power from indoor unit & communication is with single core cable.
In this case connect a new temporary cable from indoor to outdoor with no switch or isolator to prove if the problem is with interconnect cable or units.
M series can loose communication if the communication cable is switched though a switch or isolator as the contacts can become corroded & stop correct communication between indoor unit & outdoor unit.

[BigDeal]

i noticed that the core line voltage is fluctuating between 12 and 24 volts ....its never steady if this makes a difference

[IPASA]

Big Deal, i know this model, i am from Mexico and we are selling this models, too.

Please tell me what is the size of your comunication wire, because you have low voltage, and i think that you have big size of wire... you have to use around cal. 12 or 14. Check this wire, and also check if you join the wires, anda replace with a new wire without joins.

Best Regards,

IPASA

[cosmaniac]

if it is a 3 phase unit check if you have a phase rotation if i am not mistaken in the outdoor unit u have 8 led on the board and L1 led starts flashing when u have a phase rotation if not check which led on the outdoor is on or flashing and i can help u from there

[coolhandlew]

I had something similar recently. Problem was found to be moisture in interconnecting cable. Disconnect at both ends and test between all conductors and earth at 500v. You will need an insulation resistance tester (megger). If you have a result of 1 meg ohm or less there could be a voltage drop on the affected core. This may affect signal.

[jbomba]

hi what you need to do is check the indoor thermistors and check for any abnormalities. You should get K ohm readings. if you have the model number i may be able to find a resistance chart for you.