Just wanted to follow up - yes was otherwise occupied with holiday activities. My parts should be here tomorrow (resistor) and hopefully I'll get some time in the evening to replace the wire with the bad insulation and the resistor. I will report back after the repairs to let you know how things went.

Bob

Following up....Replaced the resistor and fixed the wiring issue and now I get low fan when I have the AC on and jump the pressure switch. Unfortunately it doesn't come on unless I jump the switch so I am off the the shop to get the AC charge checked and potentially replace the switch.

Thanks for all the help,
Bob

Look at the eyesight at reciever/drier..if it is foamy, you are more likely to be slightly short of refrigerant then to have a bad sw. If so, just a topping off usually takes care of that. If one has decent a/c cabin temps ,but not enough pressure on the high side to trigger the sw, it needs only a few ounces added to get to fan cut-in spec.......also be aware that one can also have the correct charge and no low fan if the AMBIENT temp is low..high side pressures do not get that high at low ambient temps and that condition is NORMAL..aux fan is only called upon at high thermal load conditions ..unlike many cars , the low fan does not ALLWAYS run when a/c runs, but rather , only when the systems is being taxed. The fan circuit is only there to keep the high side in check from runaway high pressure by adding airflow across the condenser..that cut-in spec is considered in it's design..and often mis-understood.
I see many guys change the switch and then claim it was the fault b/c the fan now works ..of couse it now works..you just got the refrig. back up to full charge when you changed the sw..a topping would have done the same ...the difference would only be in the $$$$$ amount it cost you..

I thought that this switch "http://catalog.worldpac.com/mercedes...ressure+Switch" was only a Low Pressure switch - switching the compressor off in the event of ac gas being lost to the atmosphere, it has nothing to do with high pressures that being the job of the reg or green HP switch

Your link does not work, but most all comp low refrig [30psi] are a bi/sw that also cuts out comp at extreme highside pressures.. like this one

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=23O0HOZY623O0HP54S&year=1993&make=MB&model=400-E-001&category=R&part=A%2FC+Pressure+Switch

The high side pressure sw for aux fan [ mis-labeled temp sw]has nothing to do with comp cut-out, it only controls fan cut-in/out.

Thanks Arthur, I have have certainly learnt something.