CLS REAR SCREEN/SAM ISSUE

[The Smudger]

Hi all, got into the CLS this morning, and noticed the rear screen demister was not working. Did a quick search on here and noticed a thread that mentions/links the rear screen demister with the rear SAM. This makes sense a it will be a heavy consumer and the screen/relay/battery are in the rear.

So, went to the rear SAM and checked the fuse (f10), all OK. Now my background is a bit technical so i sort of thought the demister, being a heavy consumer (40A fuse so potentially working on a current flow of around 25-30 Amps) would be working on some heavy gauge wiring possibly 1.5-2mm on the load side of the circuit. So, removed the carpet/trim and revealed the SAM, then removed the NAV unit and swung out of the way, and unbolted the SAM.

Straight away the issue was apparent. The RED coming from the back of the SAM at F10 position was clearly burnt (see image 2448), and had overheated at some point. This of course would cause a very high resistance in that line, which must be the load side of the demister relay, which would of course cause it to not work.

I have done a temporary fix as i need to renew the connector and block, just going to call MB now and see if they list the connectors and blocks separately. They should do as the block as a part No on it?

I will report back soon.

Steve.

 

[The Smudger]

Good news, MB do sell the connector block, its approximately £2.50, plus a new female terminal which is about £1, so all in all i am very happy, a cheap repair!!

 

[BIG_G_1979]

Excellent mate and good thread and conclusion thanks for sharing

Sent from my Pixel 3 using Tapatalk

 

[Major774]

Good news, MB do sell the connector block, its approximately £2.50, plus a new female terminal which is about £1, so all in all i am very happy, a cheap repair!!

I would be grateful if you can share the part numbers please. I will need do the same repair in my car.

Whilst hunting for a battery drain in my car I noticed the same wire is burnt, and the connector is missing (the wire has just been pushed back in it's position with no connector). I assume one of the previous owners failed to get this replaced. However, my rear screen demister is working, but only for a few mins at a time.

 

[DSM10000]

Excellent diagnosis and a proper fix!

 

[The Smudger]

I would be grateful if you can share the part numbers please. I will need do the same repair in my car.

Whilst hunting for a battery drain in my car I noticed the same wire is burnt, and the connector is missing (the wire has just been pushed back in it's position with no connector). I assume one of the previous owners failed to get this replaced. However, my rear screen demister is working, but only for a few mins at a time.

Hello, No problem! I would however refrain from using the screen as the problem is that the more the screen is used, the hotter the terminal will get, worse case scenario is the terminal out of the SAM may get too burnt meaning you can't use it? I am waiting for the parts to arrive and will let you know the part No's when they do.

Something else i am looking at is using a different terminal (male) out of the SAM. i.e. that connector the red wire is in has 5 housings, and 5 male terminals matching. Now that means that if your car, for example, doesn't have Airmatic, then the fuse is not fitted, but the SAM will still have a designation, which is just not used?

When i do the permanent fix on mine i will do a step by step pictorial guide showing what i mean, but fundamentally i may just use a different terminal, as the demister fuse one on mine is a little heat damaged, it would just mean changing the fuse designation so as any new owners don't get confused!!

I'll be receiving the parts next weekend, and weather permitting will fix it then.

Regards,

Steve.

 

[Major774]

Oh... thanks for the tip... I will leave the demister button for the time being until sorted.

I will need to find time over a weekend to see how much damage the SAM has taken.

Appreciate the support.

 

[The Smudger]

You are welcome!