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Old 11-04-2020, 03:46 PM   #1
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THOR #18316
A/C Fuse Problem

Hello. When we arrived at the campground on our last trip, we had to wait for a couple of hours before we could move to our site. I turned off the inverter and ran the generator and the air conditioners. When at the site and ready to set up, I shut down the generator and the A/C's and then connected to shore power (50A service on '16 Hurricane 32N). When I tried to start up the A/C's and after a bit of searching found the 15 amp fuse shot (labeled appliances). After replacing the fuse, everything worked for the week. We then moved to a different campground and repeated the same process with the same result - a blown fuse. Any idea why that would happen and what the solution might be? Thanks in advance.

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Old 11-04-2020, 03:53 PM   #2
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You wouldn't have fuses for the A/C. You would have breakers. Are you saying you are tripping a 15A breaker for the A/C unit.

What size is your A/C unit? Most are on a 20A circuit and not a 15A circuit.
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Old 11-04-2020, 04:06 PM   #3
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Actually the control circuit is 12v and is connected to the furnace control circuit. It is a 15a DC fuse that is blowing. That took me awhile to figure out especially with the vague fuse labeling. Thanks.
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Old 11-04-2020, 04:16 PM   #4
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So if it is the DC Control Circuit fuse is blowing, that would tend to eliminate any issue with the AC voltage causing the fuse to blow since they are two separate circuits.

You are saying the "Appliances" fuse is blowing. What other items are not working besides the A/C when that fuse blows?
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Old 11-04-2020, 04:36 PM   #5
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True, I am not sure about other
things on that fuse except the furnace and maybe the thermostats. I guess I need to check their wiring.
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Old 11-04-2020, 04:46 PM   #6
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It would be worth pulling that fuse to see what other 12V items are on the circuit. It is possible something else other than physically running the A/C is causing the fuse to blow.
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Old 11-04-2020, 06:26 PM   #7
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The appliance circuit would be The Refrigerator, Furnace, A/C, range hood if it's a single unit and WH. All gas-fired units.
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Old 11-04-2020, 06:31 PM   #8
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Also, you say you turn off the inverter, is it one that also charges the batteries when you have AC power? What is the voltage of the batteries while you are doing these changeovers?
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Old 11-04-2020, 06:46 PM   #9
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Thanks everyone and sorry for the delay. I've been driving. Good to know that the fuse has all gas appliances on it. My refrigerator is 110vac only but I'll try to eliminate all the others. It's odd that everything seems to operate although I haven't run the furnace itself. The only time the fuse is a problem is after turning the genset off and plugging into shore.

The inverter is not a charger, it's the Xantrex 1800. All battery voltages are good in all situations (both charging and when inverter is on).
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Old 11-04-2020, 06:49 PM   #10
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I failed to mention that I have changed the thermostats to Honeywell digital but the too have worked great.
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Old 11-04-2020, 07:17 PM   #11
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Have you been driving through rain? It is too common for the furnace control board to get wet especially with your vintage coach. Even if not wet, the corrosion on the control board could be causing an intermittent short as you drive down the road and blowing the fuse, but you don't see it until you have setup camp and the A/Cs don't work because the thermostats have no control power.
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Old 11-04-2020, 07:28 PM   #12
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Yes, we drove through heavy rain for about 8 hours the first day. Thanks for the tip. I'll check that out.
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Old 11-04-2020, 07:39 PM   #13
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Yes, we drove through heavy rain for about 8 hours the first day. Thanks for the tip. I'll check that out.
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Old 11-06-2020, 06:11 PM   #14
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So I think that I have isolated my problem to either the wiring of the Honeywell thermostat or the furnace control board. Whenever I move the slider switch to heat, it pops the 15a appliance fuse. I didn't think I did that twice on my last trip, but I've done a lot dumber things. As mentioned, the control board does not show signs of moisture or corrosion. I know that they do crap out sometimes but I'm hoping that I did something stupid when wiring the digital thermostat. A/C and fan works fine as long as the fuse as good. Here are some pics of the thermostat. I sure appreciate any feedback you fine folks can provide.
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Old 11-06-2020, 07:16 PM   #15
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Quote:
Originally Posted by reminckv View Post
So I think that I have isolated my problem to either the wiring of the Honeywell thermostat or the furnace control board. Whenever I move the slider switch to heat, it pops the 15a appliance fuse. I didn't think I did that twice on my last trip, but I've done a lot dumber things. As mentioned, the control board does not show signs of moisture or corrosion. I know that they do crap out sometimes but I'm hoping that I did something stupid when wiring the digital thermostat. A/C and fan works fine as long as the fuse as good. Here are some pics of the thermostat. I sure appreciate any feedback you fine folks can provide.
Here is a good simplified schematic for your Atwood furnace:


You can see in this diagram that you should be able to turn the "breaker/reset/power" switch on the furnace to OFF and still have control power back to the thermostat, but in my experience that is not always the case as the BLUE wire is attached to the downstream side of the switch.
In any case, turn the furnace breaker/switch off, jump 12 VDC to the blue wire to power the thermostat, then try to turn the furnace on at the thermostat. It obviously will not come on, but the thermostat will send the "ON" signal to the furnace.

If the fuse does not blow, then the thermostat wiring shoild be OK but your problem is likely in the control board or maybe the fan drawing too much current (can you manually turn it?)

If the fuse still blows you have a problem between the thermostat wiring and the relay on the control board.
You can further isolate the control board by removing the wire connection plug from it but you will definitely need to jumper the 12 VDC to the thermostat at the plug to provide power to the thermostat. If it still blows the fuse then you either have a wiring problem with the thermostat or between the thermostat and the control board plug.

Good Luck
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Old 11-06-2020, 08:23 PM   #16
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Thank you very much. It'll likely be this weekend before I can follow your troubleshooting advice but I'll let you know how it turns out.
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Old 11-06-2020, 10:27 PM   #17
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Hey Ted, I did make it back out the coach a few minutes ago. I turned the switch off at the control board. I jumpered across the two wires which I had removed from the switch at the control board. When I did so, the fan started (I had left it in run on the thermostat). I turned the fan to auto and switched to heat and the fuse popped. So, based on your advice, it looks like a problem between the thermostat and the control board. Correct?

Does it look like the thermostat is wired correctly as far as the heat circuit is concerned? Now that I think about it, I can't remember why I put those two blue wires in with the large white and black. Now I'm thinking that the two blues should wired together without anything else. Thanks again.
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Old 11-06-2020, 10:48 PM   #18
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Old 11-06-2020, 11:25 PM   #19
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Thanks but these wire colors don't match with what I am working with. I do see that he added a switch to choose high or low fan setting which I have not done yet. I may in the future but my A/C has worked great since the thermostat changes. That is as long as I don't turn on the furnace.
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Old 11-07-2020, 02:48 AM   #20
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I connected mine according to the diagram that came with the thermostat and it blew the same fuse. Then I connected according to the diagram without high low switch changed fuse and everything was fine
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