Side by side westinghouse

A friend has a big side by side westinghouse fridge, a WSE6070SA, that's not cooling. I don't repair domestics anymore, but I thought I'd take a look.

I went to have a look at it, and as normal, the evap coil was iced up.
This fridge doesn't have any thermistors on the evap coil, which is strange because it has a digital LCD control panel to set the temperature in the fridge section.
On the freezer evap it has just a thermal fuse and klixon, just like all the old mechanical frost free fridges.
Anyway, the fan, heater element, klixon and thermal fuse is OK, so what controls the defrost?
There's no defrost timer, just an electronic PCB near the compressor. Does that control defrost? how does it control defrost?
Anyone got a service manual for these side by side westinghouse fridges?

dunno bout manual but i get my parts from http://spares.bigwarehouse.com.au/ if that any help plus you mite get the parts quicker than me as takes weeks to be sent over here :)

hi, was the ice build-up at the evaporator also over the drainage hole, if so water that should go down the hole is freezing so each time on defrost adding more ice. you need to hang some thin copper wire from the defrost heater into the drainage hole and it acts like an extension to the heater.