Mercedes: 1984 Mercedes 190E Rear window defogger, fuse box, time relay

Question
The switch light works when activated but the glass does not defrost/defog. The book refers to a Time relay in the fuse box area but none of the schematics show it alone. The only relay is R1 a large relay incorporating flasher, wipers and rear defogger. The flashers and wipers work. How would I test the defogger function? These aren't cheap and the dealer won't take returns if it is not the relay. There are no breaks in the rear window grid.

Answer
Rick,
You may be able to remove the relay and check the terminals for continuity. I do not have schematics for this vehicle. If you can remove the connecting wires to the window element, you should check for continuity there as well. Sometimes a break can occur in the window grid that is not visible. I would also check the wires coming to the unit. You should have 12 volts there if the relay or switch is working properly.
The relay is designed to take the amperage for the heating element. The switch just operates the magnet to open or close the relay depending on the circuit design.
Hope this helps.
Good Luck
Rob