Toshiba Modular Multi

[andy c]

Hi Guys, I'm after some help.
I have a Tosh Modular Multi MM A0280HT Inverter Heat Pump, with seven indoor fan coil units. The system is running with a low suction pressure (1 Bar) and the gas bypass valve SV2 is energised to try to maintain a correct back pressure, but is causing the compressor(s) to trip by internal protection. I removed the refrigerant R407c and found the charge to be correct. I checked the resistance on the thermistors, and found them to be correct. I tried to energise the PMV-A (1+2)manually but they don't appear to want to operate manually, although PMV-B would operate manually. I spoke to Toshiba Technical and we've talked through the job, but have got to a point where it can only be the PMV's or the board.
Has anyone experienced a similar problem, I would appreciate your help.
Thanks . Andy C.:confused::eek::eek::confused:

[The Viking]

First,
Have you got the service manual?
If not then you can download it from my site HERE (http://www.the-viking.eu/down.html)

Secondly,
We do need some more info.....
-Does it happen both in heating and cooling?
-When it happens what is the discharge pressure?
-When it happens what is the liquid line pressure (by the shut off valve)?

Just for starters....

[andy c]

Thanks Viking, I do have the manual already, The Discharge pressure is 24.3Bar, I didn't have the liquid line gauge attached at the time. I am back there in the morning, hopefully it wont be wet n windy like today. I could only run it in heating today cos a room full of women were shivering and complaining. I will be running it in cooling to find out its symptoms and hopefully the Tosh tech guy will have done some bedtime reading, and come up with some possible answers. I shall report any further findings here, as and when I have some. I have a new pcb available to fit if necessary, and am contemplating whipping one or both of the valves out and the strainer to see if they are blocked, the previous a/c contractors have replaced several refnets and i'm not convinced that nitrogen was used. Regards. Andy C.

[The Viking]

Hmmm....
In heating mode, discharge pressure of 24.3 Bar, I assume this is measured on the Gas pipe's shut off valve?
If so, there are 2 driers on the liquid line and the PMV A combo.
A pressure drop like that across a drier would show up as frost/ice on the outside of it.
I therefore assume that you got a problem in the PMV area...

There are also PMVs and strainers in the indoor units but I assume you had all 7 running and calling for heat? It's unlikely that all 7 would fail at the same time but I seen it before where 2 had failed and created similar problems.

From Thosh's manual:

PMV (Pulse Motor Valve)
1) When the power is turned on, a tap sound to initialize PMV is heard. If this sound is not heard, PMV operation
error may be present. However, this sound may not be heard at a place where outside noise takes prominence.
2) Do not remove the driving part (Head part) of PMV during operation.
3) When replacing a PMV set, never operate the unit with the “head” part removed.
4) When removing the driving part and attaching it again, push in it securely until a “click” sound can be heard. Then,
turn the power off, and turn on again.When you turn the power on can you hear PMV A resetting? (a long screwdriver can be useful here)

The next step would be to borrow a pcb from another unit, if you got one on site...

Good hunting,

[andy c]

Thanks for the advice, I think I’ve sorted it out now. After several head scratching sessions, and trying various things, I decided as a last resort to change the main pcb. I wanted to make sure non of the other components were faulty first, so as not to blow the new board. The original pcb was not driving the PMV’s although when I switched the power off and back on again, I could hear the valves operating. After changing the pcb, I cleared the faults at the controllers and everything burst into life. I was then able to monitor the conditions and found I was now getting the correct pressures and temperatures without the SV2 valve dumping hot gas back into the suction. Regards, Andy C.:)