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Dometic thermostat problems


Jaydrvr
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Our a.c. system quit today and none of the usual resets are working. I can't see how to open the Dometic thermostat to check the connections and I don't wish to just break it off the wall. There doesn't seem to be any useful info available online, or on my go-to, YouTube. Surely, someone knows how to do this, probably many someones... Just not this someone. TIA Jay

Edit: The zone 1 number is blinking continuously, regardless of what I do. I'm assuming that's a communication issue?? I did initially have the E1 code. I'd like to eliminate everything at ground level before I venture up on the roof.. Which I may never do....

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21 minutes ago, Kirk W said:

Which Dometic thermostat do you have? I did some poking about on Google and I think that one of these two documents may be helpful. 

20 page Dometic operating instructions           1 page E1 error recovery instruction

61kDGLZjYwL._AC_UY436_FMwebp_QL65_.jpg

Thanks, Kirk. That's the one. Usually a simple reset clears the code and it works, but not this time. I've done resets, hard resets, reset to factory default, but nothing works. Trying to avoid climbing the ladder, but I guess that may be unavoidable. Jay

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1 hour ago, Kirk W said:

I checked with Bryant RV's website for service manuals and he does have this information on the diagnostic mode for your thermostat. It shows dip switch positions, but does not show how to access them???

Yeah, I have yet to figure out how to get into the thermostat control itself. Dip switch positions must be correct - the system's been working for years. Thank you for that diagnostic! That's more than I've been able to find. Jay

Edited by Jaydrvr
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  Did you follow the reset procedures on the instructions

  If I remember correctly you may need to hold the mode and zone down for 50 seconds.   Or maybe longer.   Brain dust is moving in my head. Thinking.     This thermostat may need a certain time to reset it. As in holding the buttons down.

 

  Last time I did one of that model I called Dometic tech service and the tech said about a certain amount of time. At least I think so.

 

  Vern in a T-shirt 

Edited by Wrknrvr
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5 hours ago, Wrknrvr said:

  Did you follow the reset procedures on the instructions

  If I remember correctly you may need to hold the mode and zone down for 50 seconds.   Or maybe longer.   Brain dust is moving in my head. Thinking.     This thermostat may need a certain time to reset it. As in holding the buttons down.

 

  Last time I did one of that model I called Dometic tech service and the tech said about a certain amount of time. At least I think so.

 

  Vern in a T-shirt 

Okay, thanks. I didn't hold it down that long. I'll try that. Thank you. Jay

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2 hours ago, Star Dreamer said:

If the error code does not reset or keeps coming back then you need to fix the problem that is causing the code not just resetting the code. May need to find out what causes that error code and then troubleshoot each item.

Thanks. It's always E1, which is a communication code. Apparently, that's a common problem with this system and the flimsy Ethernet type cable used. The code reset, but now nothing's working. Jay

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Is the thermostat on a slide where it moves in and out? If so that may be where the cable is having issues. We had customers that wanted us to use a regular Ethernet cable in their elevators and we always had to tell them it won't hold up to the constant bending of the traveling cable that goes to the elevator cab. Were you able to get the unit apart to see were the cable is attached and can you run a separate temp cable from there to the other connection?

Edited by Star Dreamer
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5 minutes ago, Star Dreamer said:

Is the thermostat on a slide where it moves in and out? If so that may be where the cable is having issues. We had customers that wanted us to use a regular Ethernet cable in their elevators and we always had to tell them it won't hold up to the constant bending of the traveling cable that goes to the elevator cab. Were you able to get the unit apart to see were the cable is attached and can you run a separate temp cable from there to the other connection?

Great idea, but no, it's not on a slide. I haven't been able to get it open to check the connections or to run a test long. Thanks for your help. Jay

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Roof time sorry... Check the connections  of the phone like cables. Corrosion is possible. They are under the return plenum. Where all cables and power wiring come in from ceiling up into unit. 
 

Had same fault before no resets fixed. 
 

Found totally corroded connection. Mine was on the # 3 AC rear, but had no zones showing and E1 fault. Fixed connection and was good. 

Edited by billr
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30 minutes ago, billr said:

Roof time sorry... Check the connections  of the phone like cables. Corrosion is possible. They are under the return plenum. Where all cables and power wiring come in from ceiling up into unit. 
 

Had same fault before no resets fixed. 
 

Found totally corroded connection. Mine was on the # 3 AC rear, but had no zones showing and E1 fault. Fixed connection and was good. 

Thanks for the info. I guess I'm headed up there tomorrow. Jay

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  If you replace the end of the phone cable. Absolutely make sure you install the new end just like the old one. I normally will cut a extra 1/2” of the wire off. Then there is normally a little line on one side so to reference the order of the wire colors.

  They probably have the ends reversed from a phone connection. But you could make one up with reversed ends. Look at the color of the wires and just duplicate it. If you have a extra cable made up you can take the thermostat up on the roof and test it right at the control board.

 

  Be safe ,   Vern in a T-shirt 

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17 minutes ago, Wrknrvr said:

  If you replace the end of the phone cable. Absolutely make sure you install the new end just like the old one. I normally will cut a extra 1/2” of the wire off. Then there is normally a little line on one side so to reference the order of the wire colors.

  They probably have the ends reversed from a phone connection. But you could make one up with reversed ends. Look at the color of the wires and just duplicate it. If you have a extra cable made up you can take the thermostat up on the roof and test it right at the control board.

 

  Be safe ,   Vern in a T-shirt 

Thanks, Vern for all the helpful advice. I'll of course watch for color matching. That makes sense. I've never had good luck replacing a phone cable end, but then I've never had a decent tool with which to do it. Generally,I would just replace the cable. Obviously, that won't do here, so if that's the issue, I guess I'll be "practicing" and probably buying a decent tool. Thanks for all the advice. Jay

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   I would go find a tool to replace the ends. Check to see if your thermostat is a 4 or 6 wire communications cable. While at the store buy a short cable and ends to match. That way you can test the system while on the roof. Instead of up and down the ladder or communicating with some one else at the thermostat. Also you could possibly test what is happening on the board also.

  My rear thermostat quit when there was snow on the roof. Installed a new thermostat after trying to reset the old one. Nothing worked.  15 degrees out, snow on the roof———.   ———.  

  Just installed a new wire from blue wires on furnace and a mechanical thermostat inside for the rest of the winter.   So I will take a test communication cable and thermostat on the roof in the next few weeks to see what is wrong. I found a new control board yesterday in my rv parts.

 

  Yep, pain in the.      But good exercise up and down the ladder.

 

  Stay safe,    Vern in a T-shirt 

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   I would try and call Dometic tech for info. Hopefully they will help. I am a dealer but cannot give my dealer number out to the public.

  Also if you have two ac units that are the same, you could swop the control boards. That is with the breakers turned off. Also if you swop them make sure u take a picture of how the dip switches are set on each board. There may only be a dip switch for the second ac unit. The older units had all set for the first ac unit. That maybe confusing.  Just make sure how the switches are set on the front and the rear. 

 

   Hope this is helpful,    Vern in a T-shirt 

   If al else fails it looks like you may need a new thermostat. Now if by chance you have someone near by with the same thermostat. And they are willing to lend it to you for a test.

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17 minutes ago, Wrknrvr said:

   I would try and call Dometic tech for info. Hopefully they will help. I am a dealer but cannot give my dealer number out to the public.

  Also if you have two ac units that are the same, you could swop the control boards. That is with the breakers turned off. Also if you swop them make sure u take a picture of how the dip switches are set on each board. There may only be a dip switch for the second ac unit. The older units had all set for the first ac unit. That maybe confusing.  Just make sure how the switches are set on the front and the rear. 

 

   Hope this is helpful,    Vern in a T-shirt 

   If al else fails it looks like you may need a new thermostat. Now if by chance you have someone near by with the same thermostat. And they are willing to lend it to you for a test.

Thanks, Vern for all your great ideas and helpful assistance. I went up this morning and checked the communication wires and plugs. Couldn't really see anything without disassembling it further, but I did manage to get it running. That tells me it's a communication issue like I thought it was. All along I thought it was a bad connection. We're good for now and I'll tackle a permanent fix later when I have the time. Thanks to all for helping. Jay

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2 hours ago, Jaydrvr said:

I went up this morning and checked the communication wires and plugs. Couldn't really see anything without disassembling it further, but I did manage to get it running.

If you can remove the cable plug and put it back, that my have cleaned things a little. Before you replace the cable, try using a good quality contact cleaner on the plug and its receptacle. 

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1 hour ago, Kirk W said:

If you can remove the cable plug and put it back, that my have cleaned things a little. Before you replace the cable, try using a good quality contact cleaner on the plug and its receptacle. 

The cable plugs are facing down into a cavity that makes it pretty inaccessible without disassembling further, so I jiggled and moved then around as best I could with my pinky to scrub the contact surfaces a bit. Once I can get further in there to remove them, I'll determine if they can be cleaned and treated with DeoxIT, or if the plugs have to be replaced. Jay

Edited by Jaydrvr
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If you remove the filter panel on the ceiling, you will see a metal box.  If you are lucky, you will be able to remove a screw that holds the cover on and then can see the circuit board inside.  We had the Zone 2 box fail years ago due to corrosion on the board and the phone wire connection.  I ended up buying a new box and replaced it.  That was seven years ago and have had no issues since.

corroded AC board 2.jpg

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13 minutes ago, 57becky said:

If you remove the filter panel on the ceiling, you will see a metal box.  If you are lucky, you will be able to remove a screw that holds the cover on and then can see the circuit board inside.  We had the Zone 2 box fail years ago due to corrosion on the board and the phone wire connection.  I ended up buying a new box and replaced it.  That was seven years ago and have had no issues since.

corroded AC board 2.jpg

Thank you much for that information. I really appreciate it. Our A.C. is not accessible from below. It feeds into ductwork. Since I'm no longer comfortable spending much time on the roof, I dropped it off at my local shop. Let them "take the fall" for me. There are some benefits to getting older. Jay 

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  • 7 months later...
5 hours ago, Bojack said:

Hey my furnace won’t turn off, and when I cut all power and turn thermostat off and reconnect power the furnace comes on by it self, had to pull the fuse to keep it from coming on. Help!!

Wish I could. I had nothing but problems with the RV thermostats and now with my Mini Split system I am so happy. Set it and forget it, well not really. I wish it was like the thermostat in my car where you can actually do that and it will activate the heat or cooling to bring to your desired temp.  I thought the "AI" button on the system did that for a bit the first time I used it, but the next time I tried it seemed to stick on what ever I used last. Cooling or Heat. Am planning on a "Service" call soon and hopefully the tech will give the system a clean bill of health and explain the "A I" setting. 

 

 

Rod

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