[W126 Coupe] Looking for a short in the A/C circuit.

[Ernest Stephens]

Dick,
I'm not having problems with my fuse blowing at this time but I was impressed with your instructions and thought it worth archiving for a later time should I need it.

You ask if there is a faster way to trouble shoot the problem and I'm thinking that for the price of a fuse or two that you might disconnect the most likely component one at a time until you find the offending component.  Unless two or more components are simultaneously overloading the circuit this might be the faster and easier to resolve it, whaddya think?

Thank you for sharing your knowledge with us.
steve   
  ----- Original Message ----- 
  From: Dick Spellman<mailto:dick.spellman at gmail.com> 
  To: Mercedes Coupes Mailing Lists<mailto:mbcoupes at mbcoupes.com> 
  Sent: Sunday, September 06, 2009 9:50 AM
  Subject: Re: [W126 Coupe] Looking for a short in the A/C circuit.


  Hi Dan,

  You are on the right path to eliminating whichever component has 
  developed a short.

  I see 5 components that share that fuse 5 circuit. Monovalve, aux water 
  pump, aspirator blower, vac. switchover valve, acc pbb control unit in 
  the wiring schematic.

  Disconnect monovalve (sounds like you have done this)
  Disconnect auxiliary water pump (this shares the same cable loom (in 
  series) as the monovalve and is below the monovalve assembly
  Disconnect he aspirator blower (this requires you remove the passenger 
  knee bolster and reach up onto the shelf (careful sharp metal lip) just 
  to the right of the glove box door, locate the holder and the small 
  motor with blower (basically a small barrel on its side), wire leads are 
  very small gauge (careful not to break) and unplug the 2-wire connector 
  from blower.  If you remove the assembly careful on disconnecting the 
  hose that goes up the a pillar to the courtesy lamp air grill.
  this leaves the acc pushbutton unit it self
  Disconnect vacuum switch-over valve...with passenger knee bolster 
  removed you can probably see and reach the vacuum switchover valve that 
  sits to the right (vertically mounted next to the acc pushbutton 
  control) if it's not visible with knee bolster down, remove the side 
  carpet panel on the passenger side of center console (remove the one 
  screw in foot well that secures carpet on its face, pull carpet from 
  floor area forward then release the plastic tabs pulling downward until 
  carpet panel is free) disconnect two electrical leads to vacuum 
  switchover valve))

  If after these 4 are disconnected (leave acc control in) the fuse holds, 
  you know the acc control is okay and the individual wire harnesses 
  feeding each component are okay.  If it still blows, the control is the 
  likely culprit or it could be a dead short on any of the wire looms. If 
  you find it still blows, disconnect the acc control (I am not going to 
  write this up here, it's in the archives) and go though each of the 
  harness testing for high resistance and shorts to ground.  I'd then 
  meter each of the devices for heavy resistance or just plug one 
  component back in at a time until you blow a fuse if the harnesses are 
  okay..

  Let me know what you find. hey, there may be a faster way to 
  troubleshooting this, but, that's how I'd go about it given my limited 
  non-mechanical experience.

  Regards,
  Dick


  Dan Stratton wrote:
  >
  >> Are you saying the small control fuse in the fuse box is blowing or the
  >> 25-30 amp foil blower fuse up in the holder on the firewall is blowing?
  >
  >
  > Dick,
  >
  > It is the small fuse in the fuse box. (at location #5)
  >
  > Dan
  > The MB Coupes Website!
  > W126 SEC Mailing List
  > Postings remain property of MB Coupes, L.L.C.
  >

  The MB Coupes Website!
  W126 SEC Mailing List
  Postings remain property of MB Coupes, L.L.C.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.pairlist.net/pipermail/mbcoupes/attachments/20090906/19190e26/attachment.htm>