Making Your Brain-Dead ACC Blow Cold

[ctaylor738]

Sometimes, you need some relief from the sun and the heat. This was one of those days. It was 99 in DC today with humidity that generated a heat index of 110.

My 560 had the typical problem of either full heat or full cool, except that it has become heat all the time. Desperate to get at least tepid air from the vents, I investigated.

The biggest problem seemed to be that the monovalve was letting hot water into the heat exchanger all the time. At first I suspected the monovalve, but then I read a little further. The monovalve is either open or closed as the name implies. It receives a constant 12V from a fuse, and when it gets ground, it closes. The ground is controlled by the temperature control unit which gets input from a bunch of places.

So my problem was that I wanted cool air, fast. What I did was to remove the connector from the monovalve and take it apart. I hooked the black/red (positive} wire back to the monovalve (rear pin). Leaving the brown/white wire disconnected, I fashioned a ground wire and ran it to the other pin on the monovalve. This causes the monovalve to stay closed no matter what signal it gets from the control unit so if the monovalve is good, no more hot water in the heat exhanger.

So now I can at least get air temperature through the vents on Economy, and cool if not cold air when I go to one of the compressor settings. This is not a good way to go through Winter, but that seems a long way away right now.