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

[Dick Spellman]

Dan,

One other comment.  That knee bolster wants to drop a bit on the right 
side so that that the air delivery outlet can move free of the heater 
box to the left.  So, if at all possible lower the right side a bit first.

Dick

Dan Stratton wrote:

> 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

>>

>>

> The MB Coupes Website!

> W126 SEC Mailing List

> Postings remain property of MB Coupes, L.L.C.

>