Rear defroster

[French02chris]

Hello.
So, now I live in Maine since June (2024) with my 1993 400E which has 380000.
I want to say that I kept my rotella T4 15w40 oil in the engine and have no issue starting when it is 5 degrees Fahrenheit in Maine. I let the car warm up about 10 minutes before driving (especially when the temp is 0 to 30 degrees Fahrenheit outside )

Anyway, my post is about my rear defroster NOT working!! The light on the button doesn't work & the defroster definitely doesn't work (not really a big issue, but still...)
I check the fuse and it's good (I also replaced it just to make sure)

Is there another fuse somewhere that I don't know about?? (also I have no intention of removing the front console)

Thank you.

 

[500AMM]

Unless you have been working with something else on the car potentially affecting that function I would suggest a bad combination relay, or bad contact. Try jogging the relay in & out 2-3 times, and see what happens. The combination relay sits further behind the fuse section, so you have to unscrew the covering to access the relays. It's at least and easy check to do.

This link explains fuses & relays on the W124:

Fuse box diagram Mercedes-Benz 124 and relay with designation and location

Designation of fuses and relays Mercedes 124 with box diagrams and their locations. Cigarette lighter fuse.

fuseandrelay.com

 

[French02chris]

Unless you have been working with something else on the car potentially affecting that function I would suggest a bad combination relay, or bad contact. Try jogging the relay in & out 2-3 times, and see what happens. The combination relay sits further behind the fuse section, so you have to unscrew the covering to access the relays. It's at least and easy check to do.

This link explains fuses & relays on the W124:

Fuse box diagram Mercedes-Benz 124 and relay with designation and location

Designation of fuses and relays Mercedes 124 with box diagrams and their locations. Cigarette lighter fuse.

fuseandrelay.com

I have not worked on anything affecting that function.
I went to the link about the relay.. However it's multi relay, and every thing else that the relay controls is actually working..
Thank you

 

[500AMM]

The relays are inside the fuse box on the left side (seen from the drivers position).

 

[French02chris]

The relays are inside the fuse box on the left side (seen from the drivers position).

View attachment 207083

Well... I know where the relays are... My question was which relay was it?
So I guess it's relay H (however everything else that this relay controls is working)
Thank you

 

[500AMM]

Yes, it was relay H I had in mind. I had that issue on my exLimited, so it was just my guess.

 

[French02chris]

Yes, it was relay H I had in mind. I had that issue on my exLimited, so it was just my guess.

Ok
I will look at it today or tomorrow
Thank you

 

[gsxr]

Start simple. Tap the button repeatedly, like dozens of times, and pretty hard. It's possible that the internal switch contacts are dirty and if you cycle it enough, it may come back to life. Failures of the relay are exceedingly rare IME. My money is on the switch.

BTW, it doesn't hurt to let the car idle for a minute or two after a cold start, but in general it's better to start driving it relatively soon (go easy on the gas, and RPM's, until warm though). I'd let it idle for 1-2 minutes and then drive.

 

[French02chris]

Start simple. Tap the button repeatedly, like dozens of times, and pretty hard. It's possible that the internal switch contacts are dirty and if you cycle it enough, it may come back to life. Failures of the relay are exceedingly rare IME. My money is on the switch.

BTW, it doesn't hurt to let the car idle for a minute or two after a cold start, but in general it's better to start driving it relatively soon (go easy on the gas, and RPM's, until warm though). I'd let it idle for 1-2 minutes and then drive.

I will try hitting the button!!!! ..
However as for the cold starts, with rotella T4 15w40 in Maine in the winter, 1-2 minutes idling is definitely not enough!! The car didn't like it (especially that I have to drive some hills, even at low rpm & easy on the gas)
Especially when the outside temperature is less than 25 degrees (Fahrenheit)!!!!
When I let it idle 5-10 minutes, I have no issues (everyone around where I live, let their newer cars idle 5-10 minutes.. And they are Maine natives!! Lol)

 

[gsxr]

If the car will be spending more winters outside, you might look into a block heater. This is quite a bit of work to install though, the AC compressor bracket has to be removed to access the threaded port on the block where it screws in. I've been wanting to do this on our E420 that gets driven in winter, although parked in an insulated garage, it can get below freezing in there when outside temps are near or below zero. The 1/4 mile long driveway is the warmup period, then it eases up to 70mph...

 

[French02chris]

If the car will be spending more winters outside, you might look into a block heater. This is quite a bit of work to install though, the AC compressor bracket has to be removed to access the threaded port on the block where it screws in. I've been wanting to do this on our E420 that gets driven in winter, although parked in an insulated garage, it can get below freezing in there when outside temps are near or below zero. The 1/4 mile long driveway is the warmup period, then it eases up to 70mph...

I use the car only once a week in the winter, so that's fine
Also, I just went outside now (freaking 18 degrees) and wiggle the relay as well as hitting the button for a straight 2 minutes!! It's working again!!! Thanks a lot for the tip

 

[500AMM]

I use the car only once a week in the winter, so that's fine
Also, I just went outside now (freaking 18 degrees) and wiggle the relay as well as hitting the button for a straight 2 minutes!! It's working again!!! Thanks a lot for the tip

That's great!
The switch massage is a good trick, just like the headrest switch which is rarely used and need some massage from time to time. And the instrument light switch sitting in the cluster is prone to oxide buildup on the rheostat over time and need some jogging to fresh it up. When that said, the '90 era MB switches are really durable stuff!

Yes, it was relay H I had in mind. I had that issue on my exLimited, so it was just my guess.

As for that issue on my exLimited. The error was pretty confusing because some of the functions worked fine in periods, which they shouldn't if the relay was blown. And for unknown reasons the relay worked fine when it was pushed slightly sideways. I couldn't find anything wrong with the wiring and terminals connected to the relay either. I didn't have any spare relay on hand, so as a temporary fix I put a piece of something inbetween holding it in that position and it worked fine ever since.

 

[French02chris]

Little update.. As of April 4th,the rear defroster is still working fine!!
So hitting the button a few times was definitely the way to go!! Lol