Must have been a Volvo..... or other expansion oriface, pressure cycle system. Adding a extra half pound of refrigerant won't help a cycling MB. It might tear up a compressor though if the right amount is already there. If the compressor cycles irregularly on that MB it is most likely an electrical problem..... unless you have too much freon or too much pressure cutting out the compressor. The low pressure switch is also a high pressure switch and if the fan doesn't come on and you are full of refrigerant (or too full) the high side pressure gets to the threshold of the switch (somewhere around 400psi I think) and cuts the comp out. Then at some lower pressure it comes back on.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician