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#1
06-21-2006, 12:03 PM
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Aux Fan '88 560SL
Greetings...
This past weekend, I decided to dive in under my dash to investigate a bit. I repaired my in-car temp sensor, whose hose had deteriorated. In the process of "messing around" I noticed my aux fan was not running when the a/c was switched on and pumping out cold air. After checking all fuses, etc I discovered if I shorted the wires on the red switch on the receiver/drier, the fan would run (the '88 uses a pressure switch on the receiver/drier to activate the k10 relay for low-speed aux fan). My question is... Can the switch be replaced without evacuating the system? Appearances are it cannot, but looks can be deceiving. Any ideas? 'Gonna tackle this before I head back under dash to investigate air door operation (fresh/recirc not working presently).
__________________
RM Smith 1988 560SL "Where is it again that we are going, and why are we in this handbasket"? 
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#2
06-21-2006, 12:40 PM
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It might be worth double-checking that the switch really isn't doing what it's supposed to be doing first. Maybe your fill is marginal.
I jumpered my low-pressure switch to operate the fan (low-speed) all the time, air on or not (not, because mine is probably near-empty). This was worth a few degrees on the higher end temperature excursions. I know, I know, the fan will wear out a little faster...
__________________
86 560SL With homebrew first gear start! 85 380SL Daily Driver Project http://juliepalooza.8m.com/sl/mercedes.htm
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#3
06-21-2006, 02:08 PM
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Unfortunately you can't replace the switch without evacuating the system. Wish Mercedes would have taken cues from Ford, as they put a Schrader valve there so you can remove the switch. I believe 1988 is when Mercedes went to a pressure switch instead of a temperature switch for operating the fan. The fan will not turn on until the pressure in the system reaches a certain level. Wait for a hot day to check the fan.
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#4
06-21-2006, 06:52 PM
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Thaks for the replies, guys.
Strife: Rarely ever see a bubble in the sight glass, and no short-cycling, so I believe the charge to be adequate. I should mention PO had the unit converted to 134A a few years ago... Pumps out nice COLD air, but I have not put a set of gauges on it to verify. I failed to notice if the fan switch on the drier was always hot, or hot with ignition on... Gotta re-visit the ole schematics. Your idea of jumping the fan is not that bad... I'll definitely do something other than evacuate a good charge just to replace a switch! KCM: Lately, in Alabama, Temp has been above 92F and high humidity. If I read the info correctly, the switch closes at 20bar (284psi) and opens at 15bar(218psi)...I think it was adequately warm (ambient temp) when I was checking on it. I believe you are correct on the changeout... How hard would it have been to include a schrader?
__________________
RM Smith 1988 560SL "Where is it again that we are going, and why are we in this handbasket"?
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