RMD8555 12v not working

[John David]

Doug
Caution everyone, this is a long post.
Sorry I was away. Jamman is right. You only need to hook up the 12 pwr. The D+ and S+ are signal wires. I have the 12v pwr hooked up, no d+ or S+. My fridge will NOT find and switch to 12V automatically. It will auto switch in priority to 110 then propane. I have to manually choose/force 12v and thats the way I like it, uh huh, uh huh. (wasn't that a catchy song at one time).

Front page text selection thru adobe of my manual is below. I thought it was the same as rbryan4 link but now I think about it I looked at the manual in that link a few weeks ago and decided I did not like it as it was from another country and geared to 220 v (and who knows what else is different). The manual I have I beleive I got off a dometic website. Should have kept the link but didn't. I will pm you the whole manual if you like. its about 1.5 MB.
Type C40/110
822-6114-00
TB MBA/2009
N 1
RMD 8501 RMD 8505
RMD 8551 RMD 8555
Installation Instructions

Looks like it was copyright 2009.

Here's section 4.9.3 without the pictures. (i've noted where there are pics)
4.9.3 Terminal strip
Contacts pic of back of fridge showing terminal strips)
A = Ground heating element DC
B = Positive connection,heating element DC
C = Ground electronics
D = Positive connection, electronics
D+ = Alternator signal
S+ = AES input signal from solar
charge regulator
Fig. 36 (pic close up of term strip A and B.

Pic close up of term C and D and D+S+

For MES and AES it is compulsory to provide
a permanent 12V DC supply at the terminals
C/D (permanent voltage supply for functional
electronics).
4.9.4 D+ and solar connection (only for
AES models)
D+ − connection:
n >Automatic Mode< the AES electronic system
automatically selects the most efficient energy
supply. In automatic mode the electronic
system uses the D+ signal (dynamo +) of the
alternator to detect 12V DC. 12V DC operation
is selected only while the engine is running in
order to prevent battery discharge.
on the vechicle
on the appliance
Abb. 37
S+ − connection:
12V DC energy can be optionally achieved by
mounting solar equipment to the vehicle. The
solar power equipment must be provided with a
solar charging controller with AES output (ade-
quate charging controllers available in selected
stores). The "S+ connection (Solar +) must be
connected to the respective terminal of the solar
charging controller (AES output). The electronic
system uses the S+ signal of the solar charging
controller to detect solar 12V DC.
Cable cross−sectional areas:
There are no particularly high current flows via
the D+ and S+ connection; therefore no particu-
larly large cross-section is required for these
connections (approx. 1mm² is sufficient).

As I said I will pm you the manual.

[Brian B-P]

The description is pretty clear: the intention of the AES system is that trailer battery power is never used to operate the refrigerator (only the controls). European caravans normally have separate connections to the tug for always-on power and engine-running power, making Dometic's setup easier to use. It would be straightforward in a motorhome, as well.

To wire an Escape to recognize that the tow vehicle is supplying power, without introducing the voltage drop of a diode, one approach would be to use a switch which follows voltage. When the voltage is higher than that of a fully charged battery, the switch goes on; any lower and it's off. This functionality is normall found in battery isolators and protective shutoff relays, but those have high current capacity which would not be needed. This device would switch on when either the tug is connected, or the solar system is producing power, or the shore power is connected and the converter is on. Since AC power is used in preference to DC, this might work out okay.

[dbailey]

I quick followup to this thread:

My thanks to pgdriver and rbryan4 and John David and Reace who supplied various pictures and manuals and such, and to the others who took part in this discussion.

It was obvious that my fridge was miswired -- no power to the heating elements and no extra fuse to the electronics. The shop that originally did the work agreed. Aside from a bit of griping about working with Dometic (by now I think we all sympathize) he made no excuses. 15 minutes later, it was fixed.

I also talked with another local Escape owner (not a regular on these forums, I believe) who had his fridge swapped at the same shop. Same problem.

Currently it's back on my driveway. I know the heating elements are drawing power, but in the 20 minute drive home the fridge didn't cool appreciably. I've got it running on 120v now. Once it's cooled down I'll switch over to 12v and see if it maintains temperature.

I guess it worked out to about 3 hours of my time, between researching the issue here and taking the trailer back in for repair.

Thanks again, all!