re: 1987 190E 2.3/8V 115K mi.

The a/c (and all of the climate control system) functions perfectly under most conditions, with very strong cooling output.

However, when it's approx 88+ degrees and the a/c's been running for 2 to 20 minutes or more (usually with the cabin already cooled), the compressor will start cycling in/out steadily every 1 second (on..off..on..off...), then the cabin won't hold temperature. If shut off, it will run normally then do the same thing again. Things behave perfectly normally if it's say 80 degrees ambient.

I had the same problem last summer (except the cycling interval was a bit longer, maybe 3-4 sec) fixed by my MB shop with a new evaporator sensor (#201-830-06-72).

The R-12 in the system was fine last year according to the shop and currently feels sufficient given the coldness of the air when cooling.

I believe there are several sensors/switches in the system that could cause this intermittant problem. I would prefer to replace all the ones that are prone to failure myself, rather than spend the $200+ in diagnosis/labor to replace one at a time. My question is which are the most likely suspects and which, if any require breaking into the freon system.

I am keeping my fingers crossed that it's not a compressor overheating failure!

Many, many thanks for your help.

There is a 3 pin temp sensor at the front of the cylinder head(red or green). It is for the aux. fan & overheating for the A/C system. If the switch thinks the engine is too hot then it will cycle the compressor as described. There is a 2 pin connector for the aux fan & the single pin is for the overheating a/c comp. shutoff. Try disconnecting the single pin the next time & see if a/c stays on. If that fixes it then install a new switch.