Mitsubishi Mr slim outdoor fan control

[Blackbird]

Hi,

I got called out to a Mr Slim Puh-5YK for a ductwork problem and I noticed a rattling coming from the outdoor unit.

I removed the covers and noted that liquid refrigerant was flooding back to the compressor causing this "death rattle". I put the gauges on the high side (only access on heating) and head pressures were very low & the outdoor fans seemed to be stuck on low speed causing the floodback.

There are two high pressure switches one for safety and the other for control (fan control on heating, I presume) Both switches have a resistance of 0 ohms which seems correct.

To me this looks like a outdoor control card fault - but I am always very cautious when replacing these things and like conformation.

Anybody else have any ideas/opinions?

cheers

[skags]

is there any fault history ? hold down sw2 on outdoor pcb ? should be written on cover to confirm sw1 will erase.also if wallmount control is used run a check . also i think these units must have no less than 5 m of pipe run between as come precharged for 30 witch is also its maximum most of the ones i have worked on have been used for cooling only, have replaced a few head preasure control ,had one bypass valve sticking , and one that has had alot of crap in the system and had to replace all the strainers (not a nice one) also check outdoor coil thermistor should be between 4.3 k ohms and 9.6 k ohms 10degC to 30 deg C good luck

[Blackbird]

Thanks Skags

There was nothing when I held down sw2.

The pipe run is of adequate length.

I have been out to this unit before and I was trying to remember what I did. I looked it up in my accounts and I replaced the outdoor control card 3 years ago. The refrigerant charge was OK then, but it was in the summer.


There is a wall mount control, how do you do run a check?

The outdoor coil thermistor would only be for de-ice shouldn't it? or does it control fan speed? I thought head pressure controlled fan speed.

The problem I seem to have is not enough airflow over the outdoor coil causing low head pressure and flood back of refrigerant to the compressor.

Thanks for the pointers

[Blackbird]

I did a check on the unit it indicated a problem with the outdoor board. The thermistor values were within range, and voltage output to fans is 70V. no matter what the temp of the thermister is.


I will change the board.