Fridge Cuts out When I Start the Engine

swebster · 05-16-2004, 09:02 PM

I've been chasing an intermittant issue with my fridge for almost a year. It seemed to turn off on it's own from time to time. It always seemed to be something with the 12V system and since the PO had wired an inline fuse into the 12V dist panel I thought maybe it's just shakes loose from time to time. Well today I got a little further. I noticed that the on/off switch would come back on if I pushed it. So a little di-electric cleaner and the switch is fine now.

BUT...there's more...

Now it seems to work in all modes until I turn the key to ignition start. It's fine coming on or off shore power and blows the fuse as soon as I start the engine.

I have the Dometic Diagnostic manual and understand that there is a 12V feed and Ground that should be wired right to the house batteries and another 12V for the ignition lock out but now I know why the PO put the fuse holder in there. It keeps blowing whenever you start the MH.

I have yet to chase wires, but since chasing wire is my least favroite thing in the workd to do...does anyone have thoughts on where to look...bad ground....ideas?

Here is a pic of the 12V dist panel with the inline fuse.

87MH · 05-17-2004, 06:38 AM

Quote:

Originally Posted by swebster@myrvadvanta

I've been chasing an intermittant issue with my fridge for almost a year. It seemed to turn off on it's own from time to time. It always seemed to be something with the 12V system and since the PO had wired an inline fuse into the 12V dist panel I thought maybe it's just shakes loose from time to time. Well today I got a little further. I noticed that the on/off switch would come back on if I pushed it. So a little di-electric cleaner and the switch is fine now..

I, also, had an identical problem with the switch as you have described.

Also had a problem with the main board - sent them both to:

http://www.dinosaurelectronics.com/S...0Bulletin2.htm

Rebuilt both boards for less than 200 bucks. Good people to do business with.

If I remember correctly, the source for the 12 volt heating element power is directly from the alternator, not the batteries. It is installed this way to prevent the heating element from draining either house or coach battery. The main fridge board is not supposed to switch to 12 volt power until it senses a voltage in excess of (I think) 13.4 volts. Again, a safety circuit to prevent the 12 volt heating element from draining the battery(ies).

Quote:

Originally Posted by swebster@myrvadvanta

BUT...there's more...

Now it seems to work in all modes until I turn the key to ignition start. It's fine coming on or off shore power and blows the fuse as soon as I start the engine..

Remember that once the main board senses a lack of 13+ volt power (and turns to 12 volt heating element "Off"), there is a delay of about 20 minutes before the gas burner will ignite - I think this is a safety feature such that if you pull into a gasoline station and turn off the ignition switch, the gas flame will not attempt to ignite while you are pulled up next to the pump.

Quote:

Originally Posted by swebster@myrvadvanta

I have yet to chase wires, but since chasing wire is my least favroite thing in the workd to do...does anyone have thoughts on where to look...bad ground....ideas?.

Since it seems that there were no "standards" in place at the factory when they were building these beasts, and, for sure, most wiring is unique and without documentation on each unit, once you trace a line out, permanently mark it or make a diagram to insert in your manual. Like you said, tracing wires is a PITA (especially if you are working alone), but if you document it, it might save you from having to do it again in a couple of years.

Luck

87MH · 05-17-2004, 06:54 AM

The board itself takes minimal power.

What size fuse continues to blow?

It might be that the PO (or a service tech) rerouted the wires in the main board in an attempt to make the 12 volt element run off of the connection that you showed in the picture.

Again, on speculation, it is possible that there is a connection or fuse problem in the engine bay alternator/splitter wiring (where the 12 volt power for the heating element is SUPPOSED to originate).......and the guy took the "easy" way out and attempted to get a power source for the heating elements off of the house batteries (the house batteries should supply power for board logic and the gas ignitor only -- not the 12v. heating element).

"Suck it up, spend the bucks, do it right the first time."

swebster · 05-17-2004, 08:21 AM

Dennis - thanks for the input. I'll double check the installation wiring diagrams again at lunch but I thought I saw a diagram in the Dometic manual that shows it wired directly to the house batteries (10g under 17 feet and 8g under 33 feet) and then another lead (12V lockout) goes to the acc side of the ignition switch for the 20 minute cutout. Yes this cutout is for filling stations and boy do you want to make sure that thing works!

The fuse is a little 5 amp fuse. There is another fuse on the board. BTW - I replaced the board last summer (had two spares in the AS when I bought it - hmmmmm can you say trouble spot?)

Anyway we're headed to FL on Friday and the idea of not having a cold one at the end of a long day of driving is just too much for me to bear. I guess I'll just have to start chasing wires.

swebster · 05-18-2004, 09:42 PM

A little closer to a solution tonight. I stuck a tester on the 12V positive and negative as well as the ignition cutout (they are in fact seperate circuits). Sure enough, 12V to the fridge with the ignition off, no power to the cutoff...turned the key to the acc position, same deal, started the RV and the 12V lead blew a fuse as soon as the cutout came on.

So I'm looking over the dometic info trying to figure out everything. Did I mention I hate tracing wires? To make this more fun...the wires run up into the wall behind the fridge. So something is happening to the 12V feed on engine start. I wonder if the battery isolator us the cuprit.

Next step is to put a multi meter on there and see what happens to that line on start.

87MH · 05-19-2004, 06:10 AM

Steven:

On the main board, to the right, there should be a connection point for the 110v in, in the same vicinity, there should be some heavy wires carrying 12 volts for the 12 volt heating element.

Just wondering -- could someone have jumped the output from the control board power supply (board power only, probably the 5 amp connection you pictured above) into the power connection for the heating element?

I'm pretty sure on mine that the heating element power comes from the splitter in the engine access compartment.

IF the heating elements are attempting to power up through the 5 amp fuse it would surely explain the fuses being blown.

swebster · 05-19-2004, 08:19 AM

Dennis - I think you and I are getting to the same place. I dug out the original Dometic info last night and that line should be a directly wired to the 12V coach system with a 30 amp inline fuse. My board power has been wired with a 5 amp fuse in the access compartment (listed as a bulletin from dometic).

I also noticed that it's 10 AWG going into and out of the distribution panel with that little 12 (maybe 14) gauge inline 5 amp fuse holder in there.

I'd like to know why he bypassed this in the first place....maybe he got tired of buying those special little fuses in the panel? In any case I'm going to wire in a 30 amp fuse with 10 gauge wire, soldered connections the whole nine yards.

swebster · 05-19-2004, 12:24 PM

Stuck a 30 amp fuse in there today and the problem appears to be solved. I just "farmered it" in there for now. Fridge is on, stay on and won't turn off. Started and stopped the engine four or five times. Started an stopped the genset the same...tried with engine on and engine off...could not blow the fuse.

Left it on to see if the LP kicks in. If this is it it'll be the easiest repair yet on the MoHo