AC unit has E7 error

[mikeborny]

Both my front and rear AC work when I run the generator, but when I plug into power I get an E7 error on rear AC.
The error code is no power to unit.

Anyone know why it would work under generator but not shore power?

2014 390 BH

[mikeborny]

Disconnected from shore power and took it for a quick drive and ran both AC units while driving. Put back in storage, hooked up power and now both working. [emoji848]

[Mmnsc]

You might have a loose connect on the shore power side of your transfer switch which might intermittently let power in. If it happens again that would be the first place I would look.

[planopat]

Did you turn the power off on the dometic control panel and wait a minute then power on? Might just need a reset.

[CZNEDY]

E7 error code means "Interruption of power" Switching from Gen to Street power or from street power to gen will do that. Turn the AC off before switching and you wont get the error.

[flattyattack]

This always happens to us when the power flickers on and off while the AC is running, all it takes for us is to reset the circuit breaker.

[Oscarvan]

Originally Posted by CZNEDY

E7 error code means "Interruption of power" Switching from Gen to Street power or from street power to gen will do that. Turn the AC off before switching and you wont get the error.

Not only that, your transfer switch will live longer if you download to minimum load before switching over between generator and shore or vice versa.

With a load on there's a minute amount of arcing in the brief nano second that the contacts are ALMOST touching. Many nanoseconds burn a hole.

[Oscarvan]

Originally Posted by flattyattack

This always happens to us when the power flickers on and off while the AC is running, all it takes for us is to reset the circuit breaker.

If the power is back on, turning it off and back on at the thermostat will fix it too.

[gordonsick]

The E7 Error Code says that you don't have shore or Genny power to run the AC. Now, consider that you can leave the AC setting as normal, pull out of the campground and now drive down the road. If the temperature gets warmer than the engine AC can handle, turn on the Genny from the dashboard and you've now got AC running throughout the coach. Thus, it is a feature rather than an error in this instance.

This is also handy after a hot day's drive when you want to cool the coach before arriving at your destination. This is particularly useful if you know you are going to be boondocking and the locals will frown on you starting up the Genny just before you arrive.

One of the regularly touted features of Auto Gen Start (AGS) on the Genny is to run the AC and protect pets while you are away if the temperature gets hot. There is a special Magnum ME-PT unit you can put in a Dometic AC that does trip the AGM when the AC wants to come on, but it seems to be rare as hen's teeth and I've never seen one installed. Thus, I always thought that the idea of AGS to protect your pets was just marketing nonsense.

However, when reading the Magnum manuals on AGS settings for temperature, we read that you should set the auto-start temperature for the generator to be higher than the temperature that you've set on the AC. That means you will get the E7 error code when the thermostat calls for AC, but the generator hasn't started. As soon as the generator starts on the basis of the AGS temperature threshold, and gets into generation mode, the E7 code clears and the AC starts.

To be more specific, let me quote from Section 7.0 of the Magnum ME-RC Web Rev-G manual, which I found at http://magnumenergy.com/wp-content/u...-ME-RC_Web.pdf
"Where should I set Start Temp? If you are using this feature to power an air conditioning unit, the AGS: 04 Start Temp F setting should be slightly above the A/C unit’s thermostat “cool” temperature (usually around 70-72F). Once the temperature setting is reached, the generator will start providing power to the A/C unit. The reason the temperature is set above the A/C unit’s thermostat is to ensure the A/C unit will run when the generator starts. If the AGS’s temperature setting is below that of the air conditioning unit’s thermostat setting, the generator will run, but the A/C unit is not calling for a run period or cooling; your generator is running, but the power is not being used by the A/C unit—resulting in wasted fuel and run time."

In other words, the normal operation of the AGS feature to start the AC requires that you get an E7 error code before it starts. It is a feature and not an error!

I understand Oscar's concern about arcing in the contactors of the transfer switch. But, I conclude from Magnum's discussion that they don't regard this as being a major issue. I realize that the AC units are on a 20A circuit breaker, but they only get near this 20A when starting. They have a much smaller draw when running and this is the source of any arcing that can occur in a transfer switch when you go off shore power. When you go onto shore power, the AC unit starts in a phased way with the fan first and then the generator. The transfer switch is solidly closed by the time the AC turns on.

–Gordon

[formerFR]

Originally Posted by Mmnsc

You might have a loose connect on the shore power side of your transfer switch which might intermittently let power in. If it happens again that would be the first place I would look.

other than the typical 'electronic hiccup' that can happen with any system, I would say that if the problem persists, it is more-than-likely as stated above... a possible loss of connection either within the ATS(auto transfer switch), such as a loose wire on the shore power side, or even a loose connection at the Shore Power outlet/breaker...
Removing the ATS cover, while not plugged in or the Gen running, is a good and easy way to make sure that all connections are tight. The same can be said for both the Shore Power outlet, and breaker, and the Shore Power cord end, itself.

if the A/C unit is getting power from the Generator, then the ATS is doing fine for that 'side' of the incoming power. If 'no power' on the Shore Power side, then it points to a fault there, i.e. a loose wire/bad connection.

This can be a common issue on new coaches, as while the factory tries to install and tighten properly the wiring at the point of the build, when a load is applied, and heat runs thru the wires, any 'less than tight' connection can easily become a weak point.


I'll also agree with those on the 'let the ATS do it's job' side of the discussion, as for when it comes to whether one needs to turn 'off' things before changing power supplies, such as from Generator to Shore Power, or just allowing the AGS to start the Gen, and then later shut it down, while air conditioners are running.
I don't believe the ATS 'cares' whether there is any load at the time of switching, or not. If the ATS is built to have the capacity to accept and operate under these conditions, then whether the load is 2amps, or 80amps, at the time of connection, shouldn't matter. Your ATS probably has no 'caution' or 'warning' labels to that effect, either, because it is not an issue that is inherent within the ATS design - it's actually built to do just that - SWITCH power.


but, that's just me. Five years and many, many AGS runs and shutdowns while a/c units are running, and narry an issue. The AGS is designed to do just that, and the ATS is designed to handle it without human intervention. Of course, those who use more 'caution' are justified, as well... it's their 'baby' and they feel better to handle it that way : )

[gordonsick]

My previous post seems to be hijacking the thread to some extent, and I apologize.

But, I did leave one important thing out of my explanation of ignoring the E7 code when using Auto Gen Start (AGS). That is the strong recommendation that you go into the AGS menu of the ME-RC and scroll down to "08 AGS TECH". Make sure the last menu item "AGS Mode" is set to the default "RV" rather than "Other". This is discussed in Section 3.0 Setup, Table 3-1 of the manual I cited earlier. Section 3.3.2 AGS Menu sends you to Section 7.0 of the manual to learn more about the ME-AGS-N module that we have in our units – at least that is what I have. Section 7.0, under "AGS: 08 AGS TECH Menu" says:
"AGS Mode – Allows you to configure the AGS to comply with RVIA standards. When the AGS is set to “RV”, it is automatically disabled any time the generator is manually turned on or off."

Unfortunately, they don't explain the rationale for this RVIA standard, so I'll give my observations on it. I once set my AGS to autostart and the AGS Mode set to Other. I went to fill up with fuel and turned the Genny off at the instrument panel. It kept restarting on me, which was distressing, given that the Genny exhaust is pretty close to the fuel filler. It turns out that the AGS kept restarting my generator, and this was back at the ME-RC panel.

When you set the AGS Mode to RV, and then turn the Genny off at the dashboard, it will stay off. You want this to happen at fuel stops, customs stops and in the rare event that you are stopped by the police. To get the Genny back into AGS mode, you have to go back to the ME-RC panel and turn the AGS back on as the first menu item under the AGS button.

–Gordon