AC on DC circuits?!

[chemist308]

So as some of you know, I've been having issues with my Dometic refrigerator for months--so far about 6 visits from a mobile repair guy. Dometic finally approved replacing the board which was done this week. Then the fridge started throwing an "EO" error code, which is linked to communication between upper and lower board. After some troubleshooting directed by Dometic, the repair guy is telling me that it's a Grand Design wiring issue. He's saying there's a board in my rig that could be allowing AC to travel across the DC circuits. He's telling me the fix would have to be done by Grand Design service and they'd likely have to pull down the enclosure from the underbelly.

Is this even possible? Or am I just getting a line of BS from Dometic trying to get out of more warranty work. So far it seems legit--he's got my fridge running on a separate battery and an AC power connection external to the rig. Has anyone heard of this?

[CoChris]

A bad converter (120v AC to 12V DC, which all Grand Design units have) could easily put AC "noise" on the DC bus. The battery acts as a big filter (capacitor) to help reduce the noise/ripple. Is your battery disconnect switch on so the battery is connected? Another possible source is an inverter (if you have one) back feeding noise onto the 12V DC bus. If the noise is around 60Hz (standard US AC line frequency), either or both of these case can be easily checked with any standard AC volt meter (it should read 0 or very close to 0 v AC). If it is not 60 Hz noise, a "true RMS" reading AC volt meter (preferably one that will show you frequency) will tell you the noise level. I would expect a competent electrical repair person would know this and have the equipment.

Chris

[CoChris]

A quick test for the converter causing problems would be to turn off the converter (turn off the breaker or unplug the unit). and see if the refrigerator works correctly. If it does, the converter is the problem, if not, the converter is probably OK or at least not the only problem.

Chris

[howson]

So as some of you know, I've been having issues with my Dometic refrigerator for months--so far about 6 visits from a mobile repair guy. Dometic finally approved replacing the board which was done this week. Then the fridge started throwing an "EO" error code, which is linked to communication between upper and lower board. After some troubleshooting directed by Dometic, the repair guy is telling me that it's a Grand Design wiring issue. He's saying there's a board in my rig that could be allowing AC to travel across the DC circuits. He's telling me the fix would have to be done by Grand Design service and they'd likely have to pull down the enclosure from the underbelly.

Is this even possible? Or am I just getting a line of BS from Dometic trying to get out of more warranty work. So far it seems legit--he's got my fridge running on a separate battery and an AC power connection external to the rig. Has anyone heard of this?

Chemist308--please put your rig in a signature line so those of us following posts like this know what's being worked on. (If unsure how shoot me a PM and I'll send instructions.)

CoChris gave excellent answers--so I have nothing to add regarding your specific problem. Hope it is fixed soon!

[chemist308]

Chemist308--please put your rig in a signature line so those of us following posts like this know what's being worked on. (If unsure how shoot me a PM and I'll send instructions...

Done, howson. I added my rig and as an added bonus linked previous discussions on this issue for some better visibility, as I realize sometimes discussions need to be moved to less visited areas.

[howson]

Done, howson. I added my rig and as an added bonus linked previous discussions on this issue for some better visibility, as I realize sometimes discussions need to be moved to less visited areas.

Great timing! I was reading through the Dometic RM1350 Diagnostic Manual this morning looking for the AC requirements and came across this paragraph (related to your issue) but couldn't remember who was having the problem.

SECTION 4 DC VOLTAGE
Clean Direct Current (DC) power is mandatory for high-tech circuits to operate as designed. A battery will provide straight line DC power. The converter and alternator produce DC power by a series of diodes that rectify alternating current to DC. The Dometic control system will only tolerate up to 6 AC volts on the DC line. AC ripple can be measured by a digital voltmeter set on the AC and measure at the main DC terminal block connections. Six volts AC or less is acceptable. If AC volts exceed 6 on the DC incoming line, the power source should be cleaned up. AC voltage in excess of 6 volts will affect the processor and create erratic operation. When testing for AC ripple on the DC line, always put a load on the converter. The operational range of the unit is a minimum of 9.6 volt DC to a maximum of 22 volts DC. The unit will automatically shut down at 22 DC volts or greater, and come back on when voltage has decreased to 18 volts DC. The refrigerator requires at least 9.6 volts DC for proper operation, however the panel lights will continue to be illuminated until voltage has dropped to 4 volts DC or below. Do not use the body or chassis of the RV as a substitute for either of the two conductors. The refrigerator must be connected to the battery circuit with two wires of adequate capacity to avoid voltage drop. Proper polarity is crucial for refrigerator operation. No other electrical equipment or lighting should be connected to the refrigerator circuit. Just because you can read volts, does not mean you have the amps to operate the control system. If relays buzz or lights go dim or out during operation, this could indicate there is a loose connection somewhere. As a last test, use a battery and run wires directly to DC terminal block. If the unit works ok on direct DC volts from a battery, the problem is in the coach not the refrigerator control system.

[chemist308]

Well, I forgot to mention it, but last night the fridge went back to EO error while running on a separate battery and power source. Repair guy is out until after New Years though, so I won't likely have any updates on what they do next till then. I ended up putting a small residential fridge in a shed attached to my site. That seems kinda ghetto to me, but I had to. We'll see where this goes.

Oh, and Howson, I like that Reflection 315. That model was near the top of my list when I bought this one.

[chemist308]

So Dometic has agreed to send out yet another lower control board. The EO error code means that lower and upper control boards aren’t communicating. Thing is the lower board was just replaced. I asked the tech why they won’t send an upper board and the answer I got was a they’re procedure is to first replace the lower board for this error, and they won’t send 2 at a time.

I’ve had mobile service out for this ongoing issue no less 10 times. Between this and other issues I’ve had enough. Whatever I replace this Reflection with sure as hell won’t be from Grand Design.

[TucsonJim]

I’ve had mobile service out for this ongoing issue no less 10 times. Between this and other issues I’ve had enough. Whatever I replace this Reflection with sure as hell won’t be from Grand Design.

This is a Dometic issue. They are used in pretty much all brands of RVs.

Jim

[howson]

This is a Dometic issue. They are used in pretty much all brands of RVs.

Jim

Not necessarily--if the trailer's wiring is taking out the refrigerator it's a Grand Design issue.

At the very least I understand his frustration.

In addition to the refrigerator problem, look at the list of electrical issues he's had (in his signature line)!

• 2 water heater failures (2 boards replaced)
• Bedroom USB outlets have never worked
• Dual Kitchen USB outlets fail when charging 2 devices
• Coffee bar circuit breaker trips on coffee pot with nothing else on