Bosch frost free problems

I have a Bosch fridge freezer, one of the KGU29 frost free series from 2000. The temperature in the freezer section is too high and there's a frost buildup. I'm having problems matching up the generic instructions in the repair faqs to my specific model.
What I don't get:
(1) Is the defrost timer likely to be on the PC board as I can't find it anywhere? I am thinking it's unlikely the timer has broken if it's electronic and everything else is working fine.
(2) There are five power inputs in the freezer: evaporator, fan (working), thermostat (correct resistance), "Heater-defrost", "Heater-element". Why are there two heaters? The resistance of one is 310ohm and the other, 2400ohm, which looks high - probably going to try replacing it first.
Anyone know how to get into service mode on these Bosch No Frosts? Specifically, how to force defrost mode so I can do further tests?
Thanks in advance Jonathan
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Given the number of frost free problems turning up on uk.d-i-y recently I think this is how they effectively work in practice!
I've defrosted the freezer now and temp has dropped right down, may just be easier to continue doing this once a year. Bust the hairdryer in the process though!
Jonathan
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
L Reid wrote:

No, frost free means the freezer, a fan runs when the door opens, they go for years without frosting up!
Don't know about the op's question though.
MrCheerful
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@meeow.co.uk (N. Thornton) wrote:

This is the repair strategy I am following. As I said, it's not (1), I'm thinking (2)'s unlikely, and as 2.4kOhm across a resistor for a heater sounds very high I'm planning to replace it.
If anyone else knows any better, shout, there are at least thirty KGU models all with similar workings.

Behind the readouts above the fridge

I don't live in a studio flat and I do have things to do! And how can I tell if it's trying to defrost if it's not working?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

OK. One q tho: why's 2 unlikely?

If you wire a light bulb onto the defrost element and leave it powered daytime only, it'll let you know when it switches to defrost. Its an easy method, just dont leave it in such a way that someone could get fried.
I would be concentrating on the defrost timer at this stage, and only move on if you know thats working right.
Regards, NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
(N. Thornton) wrote:

snip
Well, I wouldnt assume either of those things. Your defrost timer cuold still be mech or tronic, and theyre usually mech. Secondly, even if its tronic it would probably use a relay to do the switching, and its the switching contacts that are the weakest link with mech timers. So I'd still want to know about the timer myself.

I wouldnt put that on heater element connections myself.
Regards, NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jonathan wrote:

cooling coils to melt the accumulated ice, and the other is to keep the water fluid as it makes its way out. That's how mine (different make) is arranged.
Regards Chris
--
Chris J Dixon Nottingham UK
snipped-for-privacy@cdixon.me.uk
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.