Slk blowing fuses

[Lee G]

I have an slk 230 thats decided to keep blowing fuse 37 in the engine compartment fuse box

Symptoms so far. Its been intermitantly dproping the fuse for a couple of weeks up until this weekend. Now its gone into overdrive. The fuse governs the heater, gauges ie speedo, fuel etc.
Yesterday I drove 10miles no probs then at a set of lights the fuse went, changed it the next time I stoped, it lasted 20 miles. Then about 200 yards.
I striped all the dash out today in the hope of finding a shorting wire with no luck.
I tried puting a biger rating fuse in, that way if its a dead short it would blow, but everything works ok. Im useing a 15amp fuse for test purposes.
After striping the dash today, test drove the car, after a mile the 5amp fuse poped.
It seems to be heater related, but only when the heater is warm.
When I checked the heater fan, there was a lot of leaf debris inside the cover.

Is the heater fan fed from the 5amp fuse or is there a realay on the circuit and the heater has a biger feed.

Thanks for any help Lee

 

[anyweb]

if you dont use the heater, does the problem go away ?

if so, you know where to look

cheers
anyweb

 

[Lee G]

Tried runing the car with no heater last night, soon as I turned it on, the fuse poped.
So its defo on the heater circuit somewhere. I need to get an idea of whats on the circuit. If the heater runs stright from the switch or via a relay somewhere. And where to look for relays etc on the car

It seems a bit suspect that when I got the car six months ago there was a pack of 5amp fuses and what looked like a solid state relay in the glove box

 

[smee]

use a head lamp bulb in circuit instead of a fuse if it lights at full brightness thats a short, with the lamp lit carry on looking for the short moving the loom disconnecting items on that circuit ect, when u find it the light will dim or go out depending on the current u could olso use an amp meter in the same way but its not as visual

 

[Lee G]

Treated myself to a benz workshop manual from this seller on ebay
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=8005791938

Found that there is a speed regulator board in the fan motor houseing. four screws and the motor and board will be remooved for inspection. Allso found that there is a dust filter fitted to the air system.
Which is another line of thought, if the filter is blocked it will put more stress on the fan motor causing higher power needs.

Started the car from cold the other night, no poping of fuses. Which makes me think its the motor windings breaking down