Toshiba MAR-F104 R407c

[Hulk]

Hi looking for advice on this system sitting on Preheat/Defrost for hours at a time when asking for heating.
Have changed outdoor Coil TE sensor and gas charge is fine. When i reset system it runs away fine but wont start up in morning by itself!! just sits with Preheat/Defrost Can anyone help please?

[install monkey]

has it got a bc box?- solonoid coils used to fail on em for fun- think they should be 47 ohm if good

[Hulk]

Yip it has 2 Multi controller boxes on the system but problem seems to effect a the indoors. Could it be both boxes at fault?

[install monkey]

http://www.toshiba-aircon.co.uk/assets/uploads/pdf/sales_tools/Technical_Handbook_version_11_5c.pdf

[install monkey]

when it shows pre heat defrost in the morning before you reset it can u feel any heat going to the indoor unit?- no fresh air unit pumpin cold air in causing it to stay in preheat defrost- try adding a setback temp of say 18 deg when unoccupied

[Hulk]

No fresh air supply to units. Just ducted units with open return grille's on ceiling.

[install monkey]

is it a big ceiling void? maybe duct return air from room?- enable rc sensor to control unit instead of ret air

[Loops]

Tosh called the BS boxes Multi-Controllers and the discharge gas solenoid valve coils (marked as SVD) were very prone to failure.
Old (bad) coils were 1200 ohms
Later good ones are 1500 ohms
Not 47 ohms Mr Monkey :-)
If the SVD coils are faulty then and open circuit coil means just a coil failure. As short circuit coil is very likely to have taken the PCB as well - look for burnt opto-triacs on the board (beige coloured chips)
In either type of failure the result is no heating to one (or more) indoor unit, this will show as preheat defrost on a local controller and won't change unless cooling is selected.
Cheers
Loops

[Hulk]

It's a random problem that happens once every day or so. Only way to get it heating again is by master reset!!!( Power on and off again) then all indoors heat fine.

[Loops]

Hmm odd that it only occurs once a day, then after reset is fine. Question - is the outdoor unit running when the customer says there's no heat? If so.... Here's a long shot but check the reversing valve after defrost operation - I'm wondering if the valve isn't mechanically changing back to heat mode after defrost has finished. Reversing valves are energised for heat mode (so during defrost zero volts). Not a common problem with these systems but they are getting on a bit now and could be suffering a bit of wear and tear. Cheers Loops

[install monkey]

delete the timer schedules and run it 24/7- it may be like me - cant be a**ed in the morning but after a few hrs i get going!:p