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

[Dan Stratton]

Still dealing with this problem, I've disconnected the monovalve, aux  
waterpump, AC compressor (still blows the fuse.) I haven't figured out  
how to remove the passenger knee bolster to get to stuff under the  
dash. I've removed 3 screws on the upper edge, 1 screw lower center  
and 1 plastic screw on the console but the bolster still feels like it  
is attached.

Thanks for everybody's help (and especially Dick Spellman).




> 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

>

>