Viking downdraft ventilator electrical problem.
I just took mine a part due to the same problem. I am an EE, so I have some experience in this matter. The problem was indeed the membrane ON/OFF switch. This switch is basically just stuck on the panel like a sticker. You can literally just pull it off and stick it back on. Underneath it is 3 metal "buttons". When you press it, one of these buttons presses on a flex circuit to complete continuity. This send AC line current down to the lift motor under the gear box cover. The lift motor starts moving. After it starts, a cam hits a relay switch, which completes the circuit thru the relay. This is what keeps the vent moving up after you let go of the On/Off Switch.
At first, I through I could just clean the switch up. I figured crud got down in there. But it did not work. I looked at the switch under a microscope, and the problem is the flex circuit was actually burned thru. This is usually caused by a weak spot in the flex combined with too much current. My best guess is this switch is undersized for this application. The switch will also allow current to flow even when the relay takes over, based on how it is wired. I'm not sure I like this, as if one tends to hold the button is all the way up or down, then that just more current thru the switch for a longer time which means more heat and better change of burning thru. Of course if the switch was better quality or design, it wouldn't matter in he first place.
Anyway, I'm going to take the switch to my lab and try and put a jumper wire across the burned area. This probably will not work or it will just burn in another place in the future. So I'll probably have to get another switch. The problem will be finding a good looking one. All one needs is a Single Pole Momentarily ON switch for the application. From it, run the 2 wires the control board connector (polarity does not matter). It is all pretty apparent once you take the top cover of the vent off (4 screws, 2 each side). The cable that runs from the control pad to the unit below uses a S-Video type connector and is keyed, so you can't get it back on incorrectly. Total cost in parts will be very minimal
For you DIY, remember there is AC voltage levels running thru this switch. Make sure YOU TURN POWER OFF when working on it and know what you are doing. You can get shocked.
on Nov 04, 2015