A/C compressor cycling
 

The compressor on my 300CE seems to cycle quite often. If I'm driving on the highway I can most definitely feel it engage and disengage. Is this normal? System blows very cold and gets the car cool quickly on a warm day. I have a centre vent temperature of around 40-43 degrees on a 70 degree day when at idle. The only thing I can think of is that on a day when it isn't all that hot the compressor cycles to prevent evaporator freezing. Is my assumption correct?

You need to either make an LED code checker or have someone draw codes from the diagnostic connector near the battery. Some searching here on the forum will get details on this.

Does the CCU send a code to the computer when there is a problem with the climate control? I thought that there were no diagnostic abilites for the CCU on a W124.

No, on these cars there are several systems, one for climate control, one for abs, one for air bags, etc. The codes can be extracted from the connector near the battery with an LED. Do a search to find the details on this.

These systems and codes have nothing to do with engine management.

This might help. Probe socket 7 for A/C codes (listed at the bottom of the page). The top of the page shows which systems register fault codes at which sockets of the diagnostic plug located in front of the battery. No ABS fault codes in these years.