Don't Risk Burning Up Your Pride and Joy...........

Checking out an A/C issue, I discovered that the electrical connection on the mono valve was fried as well as the part on the magnet where it connects. Further, I found that my auxiliary water pump (located underneath the mono valve assembly) was frozen. Further checking, I found the push button a/c control unit (CCU) was fried also.

This could easily have become a fire.

On 126s, the aux water pumps have no fuses and if it fails or overloads, it fries the mono valve and CCU and creates a potential fire sale of your pride and joy..

There are several ways to prevent this:

1. Unplug the aux water pump. (the aux pump keeps the heat temp even while vehicle is at idle-that's all it does..) The plug is in plain sight between the battery and the mono valve on my 380SE. Leaving it unplugged won't harm anything.

2. OR, Put a 1 amp fuse on the wire to the aux pump.

Here is a good link:
1 amp fuse link for w123 Auxiliary Water Pump – Plug and Play! - PeachParts Mercedes ShopForum

3.Or, Install a bypass.

The cost of parts to fix is approx:

Auxiliary water pump.....$60-70
Mono valve assembly.....$200-250 (MB and aftermarket sell only the whole assembly. The magnet part cannot be purchased separately.)

CCU Control Unit............$175-230

Fortunately, I found a Pull A Part JY with an 85SE with all those parts in working condition. I decided to pass on the aux pump and will leave it unplugged. Paid $4 for the mono valve magnet and $13 for the CCU.