mitsubishi mr slim puh-4yg6

[savoc]

Hi guys need some advice. the compressor stops after approx 5 minutes of running. the 4 little led on the outdoor board dont light up. suction pressure ok. not a lp of hp fault. compressor is very hot current draw 4.5 amps. have low volage 390>399 3 phase 50hz. house temp was 30 degress c. think it is a compressor protection fault. overload or thermistor? checked thermistor on comp have power both sides. unless it reset to quickly to check both sides. motor overload is labeled 15amps i think. meggered compressor pass ok. 2.5 ohms across all windings. any answer and glues? there must be a mitsubishi expert out there on this web site.:)

[stufus]

Not familiar with that particular model,must be specific to your location.
It sounds like compresser protection alright,a bit more info would be helpful.
HP/LP actual pressures,current rating for comp.etc
Is the voltage drop a new or permanent problem.
If the house is 30c what temp is it outside?
Are the filters and coils clean ,good air flows inside and out?
Cheers
Stu

[Thermatech]

I think this outdoor unit is R22 K control split system we were installing in the early 1990's. I have a PUH-4YKSA service manual to hand & suspect that this is the same or very similar unit.

about 5 to 6 amps per ph should be ok in heating or cooling so should not be over current unless the 51C thermal relay is faulty.

On most of these outdoor circuit boards there were 8 led lights. These show the live operating condition of the unit.
LED1 = compressor on comand from indoor unit
LED2 = heating command from indoor unit
ect ect ect

The LED's can be also made to display the current fault check code by using the SW2 switch when SW3-2 & SW3-1 are both in the off possition.

Each time you press the SW2 the LED display alternates between the output operating condition & the current fault check code.
You can tell which info is being displayed as the LED's flash when displaying the current fault check code but are constantly light when displaying the operating condition of the unit.

LED4 = 63H pressure switch
LED5 = 51C comp over current relay
LED6 = 26C comp thermal switch
LED7 = coil temp sensor >67 deg C

63H , 51C & 26C are all normally closed switches so open circuit makes the fault & stops the unit.
The coil temp sensor need to measure K ohms resistance to check if its ok & confirm actual coil temperature.
Also you can get the coil temp data with another LED display function but its a bit complicated to explain you really need the service manual.

If the compressor is very hot then suspect the 26C thermal switch & system short of gas prime suspect.

[slaphead1966]

hi,i had this problem many years ago,would go into fault and came up a p8 fault ( outdoor unit trouble) but when i checked the led's on the outdoor board no fault shown! it turned out to be the evaporator coil sensor not correctly sat in the pocket,spoke to mitsubishi tech at the time and according to them the indoor unit looks at the evaporator coil sensor to see a change in temperature, if it senses an abnormal temp reading it suspects a problem with the outdoor unit and throws up a p8 fault,i resecured the sensor into the pocket and the fault went away forever! hope this helps you it may not but it worked for me.