Monovalve and ACC info/ troubleshooting thread
 

To start, I shot a video of a light bulb connected across the Monovalve to show its duty cycle under 3 different temp dial settings. This is my 85 300D where the climate control system is fully functional per descriptions in the owners manual. This is an easy temporary test to set up, however there are risks that is preventable.

Video was taken after the coolant gauge went to normal operating temp. Note the change in duty cycle of the bulb (on time vs off time).

Bulb on = no coolant flow

Bulb off = coolant flow

With temp dial turned to cooler setting (more blue showing vs red), you can see the bulb on time increasing and the off time decreasing. If you rig this test up and it does not behave similarly, it may point to problems in the climate control unit, the push button unit, the temp sensor etc.

Click to play video
http://i31.photobucket.com/albums/c3...214_113142.mp4


For the bulb, I used fine stranded wire and wrapped/ twisted it around the monovalve terminals then taped the connections to keep them from shorting to each other, then put connector back on. Warning: Make this temporary connection WITH KEY OFF or you will blow a trace in the push button unit.

http://i31.photobucket.com/albums/c3...214_154339.jpg


I will post more tests when I do them. If you have anything to contribute, please post them.

This test was done on a used OE Mercedes monovalve that came out of a W123 with a working heating system. I have a 25 ft hose between the faucet and monovalve with a loose hose connection at the faucet end to bleed off water pressure (a cloth is wrapped around it so it doesn't spray water all over the place). This video shows normal operation of this monovalve with a certain water pressure (unknown at this time). Applying power = no flow/ removing power= flow. You can hear the pressure buildup when the flow was shut.

CLICK TO PLAY!
http://i31.photobucket.com/albums/c3...219_122431.mp4



In the video below, the faucet connection is tight (no bleed off), providing max pressure. As can be seen, the pressure (unknown but greater than in the previous video) is too high for the monovalve spring to overcome and latched itself shut when power is removed. If I release the pressure, it unlatches itself.

If a pressure gauge is Tee-ed in, the latching pressure of the monovalve (spring) can be measured. I may do this up at some point but if you are up to it, please do so, take some videos and post here.

CLICK TO PLAY
http://i31.photobucket.com/albums/c3...219_122058.mp4

Interesting, a nice visual... I would have suggested using an LED instead of a light bulb as I would have been afraid of drawing too much current through the board...

That bulb draws 230 milli-amps, no concern at all.