GFI tripping, AC "E7", etc...

[Pahaska]

Originally Posted by Titus

I didn't realize that the AC could/would even try to run of off the invertor. Where does it get the 110 V power? The thermostat and furnace motor are 12V (invertor does not have to be on to run them). I assume that in the cooling mode the thermostat sends 12V to a relay at the AC unit. This relay may activate using 12V, but where does the 110 V power come from on the 'other side' of the relay when using the invertor?

The thermostat gets its 12v from the AC unit through a 4-wire telephone cable with 2 signal wires, 12v, and ground. That 12v is dropped down from 120v in the AC unit electronics. For the furnace, the thermostat simply tells the AC to connect 2 blue wires from the furnace whenever heat is needed.

This is all clear on the wiring diagrams. Since there were no wiring diagrams in my 2014.5 manual, I copied the 2017 pages which are still pretty accurate for my unit. Check on page 9-26 of the 2017 manual for the furnace/AC hookup.

The fact that the AC unit is getting any power at all from the inverter tells me that there is a wiring error in the coach. To me, the most probable wiring error would be that the wires are switched on the back of the power center with the AC accidentally fed through the GFCI breaker.

[FlyFishinRVr]

Originally Posted by Pahaska

The thermostat gets its 12v from the AC unit through a 4-wire telephone cable with 2 signal wires, 12v, and ground. That 12v is dropped down from 120v in the AC unit electronics. For the furnace, the thermostat simply tells the AC to connect 2 blue wires from the furnace whenever heat is needed.

This is all clear on the wiring diagrams. Since there were no wiring diagrams in my 2014.5 manual, I copied the 2017 pages which are still pretty accurate for my unit. Check on page 9-26 of the 2017 manual for the furnace/AC hookup.

The fact that the AC unit is getting any power at all from the inverter tells me that there is a wiring error in the coach. To me, the most probable wiring error would be that the wires are switched on the back of the power center with the AC accidentally fed through the GFCI breaker.

Not sure I agree. What I see on pages 9-17 (12V Distribution Panel) and 9-21 (Furnace and A/C Control) is all of that is run off the 12V bus through the fuse panel (no breakers, so no AC). That means the thermostat runs off 12V, so you can power it on, set it, etc., with no AC present. However, when it sends the "turn on the compressor" signal to the rooftop A/C via power control module 5A-2, it gets a "no, not gonna happen" signal back and sends that to the thermostat, which in turn displays the E7 error code. According to the Dometic thermostat user manual, E7 is no AC power, which is exactly correct.

So, I was wrong in assuming the Magnum had anything to do with the OPs GFCI issue. The A/C system is working as expected and the E7 error code is correct since the OP has no AC coming into the coach. What was throwing me off was the GFCI popping (breaker 6/7), and for that I have no idea. It might be like McRider's coach and something else is determining the behavior of the GFCI, but I don't think it's related to his attempt to use the A/C with no AC......

[txntravlr]

I'll just chalk all of this up to user error... but, I'm still waiting on that manual work pictures that shows what I can and can't do and why. You guys have been awesome with help to this gal!

[FlyFishinRVr]

Originally Posted by txntravlr

I'll just chalk all of this up to user error... but, I'm still waiting on that manual work pictures that shows what I can and can't do and why. You guys have been awesome with help to this gal!

Did your dealer go through the coach with you when you picked it up? You might want to give them a call and see if they'd be willing to set up an appointment to have a tech spend an hour or two with you and go through how the various systems work. If they'll do that, take a video camera with you (phone, GoPro, whatever) and record them while they're going through things so you can refer back to it later. There's so much to learn it's hard to take it all in so having a video reference can be really handy.

[txntravlr]

Originally Posted by FlyFishinRVr

Did your dealer go through the coach with you when you picked it up? You might want to give them a call and see if they'd be willing to set up an appointment to have a tech spend an hour or two with you and go through how the various systems work. If they'll do that, take a video camera with you (phone, GoPro, whatever) and record them while they're going through things so you can refer back to it later. There's so much to learn it's hard to take it all in so having a video reference can be really handy.

Barely... he walked around quickly pointing things out, but obviously didn't spend the time we needed as newbies!

[amirm]

On running the A/C from inverter, my 2000 watt unit can only do that when it is pretty cool outside, i.e. around 60 degrees. Anything higher and the inverter immediately faults and will shut down. The initial surge is much higher than that or possibly the power factor is pretty poor.

The solution is to put in a slow start for the compressor. It is not much of a priority for us so I have not yet bothered to do it.

[FlyFishinRVr]

Originally Posted by amirm

On running the A/C from inverter, my 2000 watt unit can only do that when it is pretty cool outside, i.e. around 60 degrees. Anything higher and the inverter immediately faults and will shut down. The initial surge is much higher than that or possibly the power factor is pretty poor.

The solution is to put in a slow start for the compressor. It is not much of a priority for us so I have not yet bothered to do it.

This is surprising. Did you end up going with the 2kW Xantrex? It has a surge rating of nearly 40A, but they don't say for how long. I suppose a soft start would cure that, but I'm still surprised it couldn't handle it. Have you tried putting a clamp on the output to see why it was failing? Just curious because I was hopeful the Xantrex would support the Dometic, because the alternative is a bit expensive (i.e. replacing the Dometic with something like a Kalori Electrik Variable Speed 12v A/C unit and pull straight from the battery bank).

[amirm]

Yes, it is the Xantrex 2000 watt inverter that I linked to in the other thread. I sure was disappointed that it couldn't handle it.

[FlyFishinRVr]

Originally Posted by amirm

Yes, it is the Xantrex 2000 watt inverter that I linked to in the other thread. I sure was disappointed that it couldn't handle it.

The generator is only 2500W and it handles the A/C just fine, so the Xantrex must be right on the edge. A soft start will likely solve that......

[Mcrid]

Status update: Replaced the GFCi breaker and all is good. They do go bad. I've replaced at least 2 over the years in the sticks and bricks.