No fault code

[Ian & Ian]

We found Mitsubishi city multi VRF PUHY-P250YHM-A running at 400 High and 100 low with insufficient heating to indoor units spoke to Mitsubishi Tech carried out various checks and advised short of refrigerent, weighed out 18kg pressure tested no leak found, re-commisssioned weighing in 13kg (correct charge) still no heating, no error codes and suction pressure in heating is 70psig with discharge at 105psig piperun within spec no additional charge req,d. Pipe temp 50oC to BC box BC to units 30 to 50oC intermittantly. Can anyone help

[Kp3]

are you a 3 pipe or 2 pipe? is the 13kgs wats in the cond supplied with it? if so there mite be additional charge req'd.

[Thermatech]

The outdoor unit must be PURY if its got a B/C box.

If the system has correct charge for installed pipe length then you might have some blockage which would cause the very low suction pressure.

70 psi = about 4 bar or -15 deg C.
We would expect 7 to 8 bar & just above 0 deg C on the suction line back from the box with all indoor units heating.
Outdoor unit is looking at the low pressure / temp & making compressor run at very slow speed. If the suction pressure was up at 8 bar the compressor would ramp up & pump more hot gas to the indoor units.

Not enough refrigerant flow from box back to outdoor unit or box dumping to much liquid back into suction line.

If it had hot gas to suction bypass fault the suction pressure / temp would be high.

Fit 2 sets of gauges to the outdoor unit. 1 set on the service valves & 1 set on the unit HP / LP ports.
This will help you see if the problem is at the outdoor unit or the box / indoor units.
Use the SW1 dips for HP & LP to make sure the outdoor unit is getting correct data from pressure sensors.

If the problem is at box or indoor units look at B/C solenoid valves & LEV valves at indoor units.

As you seem to have some hot gas at indoor units despite slow compressor speed suspect LEV valve 3 at box not letting enough liquid flash off into suction line back to outdoor unit or dumping to much.


The system is trying to cope but the problem is not bad enough for the system to stop on a fault.
Some one has just added some refrigerant on the assumption that it is SOG.