markloch

I have an '03 ML500, AC comes on, but it can take a long time (10-20 minutes) before the fan and compressor kick in. We have three other MB's of similar vintage (98 E, 00 C, 02 CLK) whose AC kicks in quickly and blows very cold. Once the ML's AC kicks in, it's cold, but not frigid-cold like the others (I haven't measured the temp at the vent).

I checked the low/high pressure when it was running in moderate ambient temperature (60-65) and it read 35 and 180. I couldn't find specs for this AC unit but generic pressure tables suggest 180 is a bit high and could be attributed to a faulty/clogged EV. Scanner shows no codes thrown.

Before bringing it to be checked by an AC shop I would like to do some more troubleshooting. I'm trying to understand what conditions need to be met before the compressor kicks in, and how to determine which aren't being met (or if they are being met, what component might be faulty. I swapped the AC fan relay with another relay known to be functioning normally to no avail, so it's not a sticky relay.

Is there a decent diagnostic/troubleshooting guide, something in MB's service manuals?

Thanks,
Mark

Plutoe

The AC control module controls the system and the start---the variables are inside fan speed, individual temp settings, coolant temp, refrig temp, cabin\outside temp, air distribution choice and engine\AC fan

If you have a good compressor and enough refrigerant the compressor will start as soon as you initiate the start assuming you have set the temp settings cooler than the outside\cabin air temp.

Based on your pressure data 180=H=13bar,that indicates to me that the compressor can't make pressure of 15 to 17 bar either because you are low on refrigerant or your compressor is faulty.

If all the variables are satisfied and the compressor does not come on, I then would suspect the AC control module as faulty or a faulty wiring system