grandcanyon9

My AC off light flashes 5 times then stays on. I checked the charge and added a little R134a, pressure is good and tracks well with engine RPM.

I had to bypass the AC computer by disconnecting the AC compressor and sending 12vdc directly to it. I could here a faint click that turns out to be some sort of internal hot gas bypass valve (ie a solenoid operated internal return valve). The AC was nice and cold and the compressor sounded good. still the AC off light remained on. I had read that I needed to have the AC fault reset in the Climate control computer by the Star Diagnostics. I found a guy on Craigs list who said he had the equipment to reset the fault. He connected his expensive looking tool and could read all the codes but could not connect to the Climate Control computer. He said that there must be a bad fuse or relay. So we checked all the fuses and did not find any blown.
The climate systems works I can increase or decrease fan speed, change dampers ect... We pulled the connector to the AC high pressure switch and within a minute the radiator fan speed up. This leads me to be leave the Engine control computer is talking to the climate control computer.

So what should I do now? Take it to Mercedes and take my medicine or keep looking for this fuse my mechanic thinks is open.

Oh Please Help I have never failed to fix my own car.

Thanks Mike

Efivehundred

Maybe you can start by getting into the A/C diagnostics mode and looking for any sensor values that are not normal.

This thread, post number two: https://mbworld.org/forums/mercedes-...diag-mode.html

grandcanyon9

I can't get into the AC diagnostic
I have not found any way in.

I have the duel zone A/C with out LCD screen