Truckfridge won't work when my EVC is plugged into shore power

[dixoncj]

So here's a new one.

I just installed a Truckfridge TF49 to replace the Norcold in my 2003 Eurovan camper. It works - and looks - great and gave me a ton of new storage space. I'll put up a post about the install soon. The TF is plugged into the electrical input for the old Norcold - the plugs even had the proper plug-ends to make it work perfectly. But here's the weird thing. When I plug into shore power, the fridge compressor won't come on. The battery charges, but the TF simply won't work. Unplug the van, and it comes on just fine. Suspecting that the EVC stock charger really is that crappy, I hooked up a nice, modern Minn-Kota charger to the aux battery https://www.amazon.com/dp/B0042T4GIW/ (2 banks, though I only have one hooked up to the aux battery currently).
Sure enough, the new charger works fine and the fridge works fine when the new charger is charging.

I'm looking for a short term fix for an upcoming camp trip. The problem with this solution of course, is that if I plug into the van's stock shore power input, I can use the interior shore power plugs, but the fridge won't work. If I plug in the Minn-Kota, I can't plug the van into shore power because the two chargers would likely destroy each other and then the fridge really won't work. Can anyone tell me how I might disconnect the old charger from the battery only while maintaining interior shore power ability on the old charger? Eventually I'll take out the cabinetry and sort this out properly by removing the old charger. But in the meantime - suggestions?

[orbeamike]

Did you get the AC/DC input TF49? How about just unplug the AC and run the TF49 strictly in DC mode.
Shore power recharges the house battery, which then power the TF49 in DC mode when you are connected to shore power.

[e&m_ghia]

We noticed the same thing on our 97 EVC, after we swapped the old fridge for a newer one... When plugged into shore power, the DC line going to the old fridge didn't let our Vitrifrigo operate. We had the AC/DC option, so we just put in an automatic switch (relay) to change power sources to the Vitrifrigo when shore power was hooked up - although there were other options to correct it, this seemed safest for the new fridge.

When trying to understand this, I eventually realized that the "DC" power going to the fridge circuit was essentially unregulated when shore power was hooked up, and had a large AC component to it. This large AC ripple shut off the fridge. It may be the same in your year & Truckfridge.

What I also discovered, on our van, was that the DC power going to the middle cigarette lighter outlet was regulated, by virtue of being "filtered" by the coach battery. So the fridge could operate off of the cigarette lighter circuit's DC power, whether hooked up to shore power or not.

I documented my goof on:
https://www.thesamba.com/vw/forum/viewtopic.php?t=690336&highlight=vitrifrigo

You might think about taking some DC & AC voltage measurements, to see if the same thing applies to your fridge & cigarette lighter circuits.