'Nother ATTABOY or more. Wilton
----- Original Message ----- From: "Jim Cathey" <[email protected]>
To: "Mercedes Discussion List" <[email protected]> Sent: Saturday, September 28, 2013 10:33 PM Subject: [MBZ] 126 heater repair, and instrumentation
The heater in the 560 SEL has not functioned properly for the past year or so, and lately I've been hearing clicking behind the dash when it's acting up. I've been relying on the seat heaters for comfort. But enough is enough, it's resoldering time! (It's also possible that the used monovalve insert has finally failed, too.) I removed the ACC controller and resoldered it. I first used the Dremel wire brush to remove what oxidation and crud that I could from the PCB. I also removed the scratchy fader and washed it with soap and water, since it looked like it was full of dried coke/coffee, then I blew it dry. I used a dab of white paint to refresh the center stripe on it, let it dry, then used Deoxit fader spray on it. I decided to try something I've been thinking about for years, I used a surplus flat red LED (from one of my son's destroyed toys, in fact), soldered its cathode lead to one of the ground pins on the top of the DEF switch, positioned and aimed so it'll shoot into the switch cap. (Lying right on top of the spring, just slightly proud of the edge of the PCB where the switch cap won't quite bump into it.) I wired the anode through a 680 Ohm resistor to the X1-9 pin that goes to the monovalve. (The LED needs a bit over 2 volts, and I aimed to keep it at 20 mA or less, which would be a 500 Ohm resistor. 680 is what I had plenty of in the junk box.) If this works there will be a detectable red glow behind the DEF switch whenever the monovalve is unpowered, which means that heat is applied. The LED will be powered through the monovalve, but at only about 20 mA, not enough to affect the valve (I hope). Energizing the monovalve, cutting off the hot water, will thus also result in the anode of the LED being at cathode (ground) potential, and no light. We'll see if this works. (I had hoped that I could use the blue side [it was a dual] to tie to the AC compressor output, but the LED had a common anode, and that won't work here. No real problem, I was running out of time and needed the car, and I'm not sure of what circuitry I would need for that anyway.) Sadly, I managed to break the temperature control dial's housing while taking things apart. I had to glue it back into place, which I _hate_ to do. I used some light dabs of Shoe Goo, hoping that it'll hold yet be reversible if necessary. Driving off in the afternoon I could just see a dim red glow behind the switch in the daylight. In the dark it was plenty prominent but not too bright, we'll see in time if the blinking becomes a problem or not. The heater was working perfectly, as it has _not_ for the last year or more. The monovalve is in the clear, assuming no further troubles. -- Jim _______________________________________ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
_______________________________________ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
