Samsung SR502NXA Defrost issues

[HelpCoolIt]

Hi Guys,
Im a commercial fridge and aircon tech, My mate owns the above fridge and everything seems to be working but it wont defrost. After a day or two the fridge starts to get warm and after pulling the back off the freezer compartment the coil is all iced up.

The fan works.
The compressor and condenser fan work
The fridge and freezer cool.... very well.
The temperature sensors appear to be fine but I don't know what resistances I should be looking for.
The heater safety/bimetal switch seems to work.
The heater measures 290ohms wich would work out to be 198 watts

Does anyone have a service manual or a list of sensor values and the heater resistance/wattage.
I could just start ordering and changing parts but I would rather diagnose it if possible to save him some money.

Thanks
Dean

[HelpCoolIt]

The compartment temperature sensors are showing close to the correct temperature.
Is there a way to do a forced defrost ?

Thanks
Dean

[cool_tech]

Hello , Sometimes the channel (duct) from the freezer to the fridge gets frozen over as the defrost element is not big enough. Turn the fridge off and let it defrost all the way. it happened to a mates fridge and it worked. We left it off for 24 hours . might be quicker in summer.
http://www.manualslib.com/manual/147390/Samsung-Sr519dp.html#product-SR502NXA

[HelpCoolIt]

Thanks, yep seems that after I defrosted it properly it hasn't missed a beat to date. Will get him to monitor it and report back if there is a change.
Thanks
Dean