C280 Rear Defrost
 

My rear defrost recently quit working alltogether on my C280. The light on the dash comes on but the window never defrosts. I have checked the fuse and it is fine. If there is something else I can look for besides an ice scraper it would be helpful!

Thanks,
Brad

Bump... I know this is an old thread but maybe someone has some insight? Turn signals work, windshild wiper works, rear defroster does not.

Heres a stab.

Try following the wires from the window. THere should be a connector nearby. With car off - check for continuity/resistance.

THen perhaps unplug it and put a test light on the wires to see your getting power back there.

You waited 6 years to bump this? That is what I call patience!! I don't have that car but I will try to offer some basic advice. I will assume you have a volt meter. If not GET ONE! A schematic is always nice but some of them can be a little hard to read anyway. The first thing to try is try to find where the wires connect to the rear windshield element. In the old days these were exposed but on mine they are not, so I don't know exactly where they are. Anyway try to find the wiring AT THE WINDOW and measure the voltage with the defroster ON. If the car is running you should measure around 12V. This is because the alternator should be providing around 13.5 but there wil be some drop due to the fairly high current the element draws. If you measure 12 volts or so then the problem lies in the element or the connections to it. If you don't measure 12V then the problem is either with the switch, or some connector or relay in between the switch and the window. Make sure you leave the window connected for this test, don't unplug anything. Sorry I can't offer more help than this! Hopfully someone else can give a more specific answer for you.

I agree with the first test but I disagree with the second.

For the first test you would disconnect the connector and measure the resistance to the window side. You should measure the resistance of the window heater element. Unfortunately we don't know what it should be. Maybe around 10 ohms?

The problem with the second test is that if you have a bad connector or relay contact it might still provide a high resistance path. What this means is if you measure the voltage with the circuit unloaded (no current flowing, IE window disconnected) you could very well measure a false good voltage. But when you connect the window the voltage would dissappear.

Heh - That is being very patient!

As to the rest - I agree with Mpolli - give his suggestion a whirl. I was just trying to breathe some life yer way....

Rear Defroster
 

Had the same problem with my 97 C280 replaced the multi purpose relay problem fixed. Hope this helps.



97 C230 OZ racing wheels,Sport Str wheel, CLK muffler, K&N air filter.
94 C280 Brabus Monobock 6 (Staggard), Autopage alarm K&N air filter.