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Old 03-07-2021, 01:51 PM   #1
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Port Saint Lucie , Florida
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2021 FC Temperature sensor for AC

We have had our 2021 FC Twin now for 1.5 months and have been taking short 1 week trips to shake out the bugs. So far the only bug is the AC. The inside temperature reads very high and the AC will freeze you out during the day. The solution has been to set the AC to around 88 F, but at night this is too high and it gets overly warm. I should mention we are in Florida. I called the dealer service department and asked them where the sensor for inside Temp is located. The thermostat is in the bedroom and the inside temp sensor is on the port side behind the front TV. In other words it is mounted on the side wall of the refrigerator compartment. Using a portable thermistor I now know the problem. The wall where the sensor is mounted is 15 degrees higher than the actual temperature in the trailer. The reason is that behind this wall is the part of the absorption refrigerator that is heated. You really donít need a thermistor to see the problem, all you have to do is put your hand on the wall and it is warmer than even the outside skin of the trailer to the touch. Has anyone else noticed this problem? Iím thinking of sticking insulation up inside that wall from the outside until I can get it back to the dealer and ave it relocated.
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Old 03-07-2021, 03:22 PM   #2
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Common issue. Same for me. Only remedy is to pull the fridge and move the thermostat, which is a serious PITA.
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Old 03-07-2021, 03:48 PM   #3
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Thanks for that insight. I thought the temperature sensor needed calibrated.
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Old 03-08-2021, 05:30 AM   #4
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Common issue. Same for me. Only remedy is to pull the fridge and move the thermostat, which is a serious PITA.
Thanks for the info. Glad (or not so glad) to hear that others have noticed it too. I wonder why the service guys at RV-1 donít know itís a common problem? Iím going to try and get them to fix it since the trailer is brand new.
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Old 03-08-2021, 05:57 AM   #5
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Common issue. Same for me. Only remedy is to pull the fridge and move the thermostat, which is a serious PITA.
I looked at it again today. My thought was to insulate it from the inside of the outside compartment, but thatís a no go because of the double walled construction of that compartment. Iím thinking I can remove the little grilled cap over the sensor and if there is enough slack in the wire, pull it out and use spray-foam insulation to insulate the backside. Iím going to talk to the dealer first and see what they say. Moving it would be best - there is another hole just to the bottom left where the TV cable comes through the wall and there is no detectable temperature differential around that hole so that area is a candidate for where to move it.
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Old 03-08-2021, 09:37 AM   #6
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You might try unscrewing the sensor and putting a small piece of insulating foam under it to decouple it from the wall.
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Old 03-08-2021, 10:56 AM   #7
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We had this exact problem.

We had this exact problem. We have had it looked at while we were at the factory having some other repairs done. No success. We had it at a local RV dealer. No success. I even bought a spare remote probe, plugged it in and put it at various places to see if that fixed the problem. No luck. A friend had the same problem. What he did was remove the black grare over the probe, pull it out about 6 inches and secure it to the TV mount. I pulled mine out a couple inches. It didnít help. Eventually I took off the air return and unplugged it from the unit in the ceiling. The unit defaults to the thermostat for both AC units. That works fine for us. At night we were most concerned about the temperature in our bedroom. During the day or evening weíre more concerned about the temperature in the back of the trailer which we can adjust manually. There really isnít anywhere else to put the remote probe. If you check the literature it is not installed according to the manufacture. So, either live with it or unplug the remote probe
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Old 03-08-2021, 03:44 PM   #8
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We had this exact problem. We have had it looked at while we were at the factory having some other repairs done. No success. We had it at a local RV dealer. No success. I even bought a spare remote probe, plugged it in and put it at various places to see if that fixed the problem. No luck. A friend had the same problem. What he did was remove the black grare over the probe, pull it out about 6 inches and secure it to the TV mount. I pulled mine out a couple inches. It didnít help. Eventually I took off the air return and unplugged it from the unit in the ceiling. The unit defaults to the thermostat for both AC units. That works fine for us. At night we were most concerned about the temperature in our bedroom. During the day or evening weíre more concerned about the temperature in the back of the trailer which we can adjust manually. There really isnít anywhere else to put the remote probe. If you check the literature it is not installed according to the manufacture. So, either live with it or unplug the remote probe

Thanks for the info. I talked to the dealer today and have an appointment for April 3rd. They said they would relocate it. Can you tell me how you unplugged it in the ceiling after removing the air return? Thatís the first place I looked, but wasnít sure what to unplug. There are 2 RJ11 plugs labeled Zone 1 and Zone 2. I assumed those were for operating the AC. Only my Zone 1 is plugged in.
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Old 04-07-2021, 08:11 PM   #9
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Same thing.

Same issue here as well. Anybody have any luck other than unplugging the sensor?
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Old 04-08-2021, 05:40 AM   #10
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Same issue here as well. Anybody have any luck other than unplugging the sensor?
I called Dometic and they said to disconnect the sensor. The only other alternative is to move it. I have had my FC at AS for a week now. First they said it had to be moved, which would involve tearing apart the interior to get to it. We then discussed getting a new sensor and just putting it in the intake side of the air conditioner under the screens i the center of the trailer. I then told them what Dometic told me ad they said they would try it. Yesterday they told me it didnít work. They said the air conditioner still came on but it would not cycle.

Looking at wiring diagrams and talking to Dometic what AS tells me makes no sense. There is an onboard sensor in the thermostat and once the remote is connected it should default to the onboard sensor.

My question is have you disconnected your senso as a fix and did it solve the problem? I really donít see the need for a remote sensor located 15 feet from the built in sensor in the thermostat on a single zone system.
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Old 04-08-2021, 05:55 AM   #11
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Since the sensor is coupled/screwed to the wall, fridge heat will cause it to be 10 degrees hotter than it really is. Add the television heat....it's a recipe for disaster.

I unscrewed the little white cage, pulled the sensor out and bent it 90 degrees so it is literally "bumping" the cone part of the white sensor cage....essentially decoupling it from the wall and measuring the temperature in that area.

I also dedicated one of the vents to "point" in that direction i.e. sensor direction so that the air is swirled/circulated over the television and fridge wall.

This method has gotten us within 2 degrees F and we've accounted for that in the set point offset to keep the trailer where we really want the temp.

I understand why they put it there....furthest from the stove/furnace/heat ducts.....but screwing it to a wall where the fridge heats it up like a Dutch oven is just piss poor design. There are many other areas they could have stuck it in....like right over the table or something.

Disconnecting it is not an option, the thermostat controls zone 2 i.e. the bedroom/rear ac and the remote is for the front AC i.e. living area....so both thermostats should be used.....if they can be set up correctly.

EDIT: Front/rear is noted from our 2019RBQ, the zones may be reversed if yours is a FB.
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Old 04-08-2021, 06:36 AM   #12
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My trailer is single AC 1 zone , so then it shouldnít matter if I disconnect right?
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Old 04-08-2021, 06:52 AM   #13
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My trailer is single AC 1 zone , so then it shouldnít matter if I disconnect right?
It depends on how they wired it....if they are using the remote zone to monitor then disconnecting it may be an issue....what zone is your AC on? Does it say zone 1 or 2?
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Old 04-08-2021, 07:46 AM   #14
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Here’s an update as of this morning 4/8/2021. I called AS in Ohio and they have identified the problem and come up with a fix. They called my dealer and gave them instructions.

Basically they pull the sensor away fro the wall and insulate it from the heat source. It sounds like it will work. I asked AS why not just disconnect it and was told that their design calls for having the temperature sensed in the “largest” part of the trailer for maximum comfort. So, there you have it. BTW - AS in Ohio was extremely helpful and even called me back after they talked to my dealer and explained the fix. The gentleman I talked to in Ohio was, John.
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Old 04-08-2021, 09:27 AM   #15
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Originally Posted by kittmaster View Post
It depends on how they wired it....if they are using the remote zone to monitor then disconnecting it may be an issue....what zone is your AC on? Does it say zone 1 or 2?
Zone 1
I have a rear bed unit
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Old 04-08-2021, 12:37 PM   #16
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Zone 1
I have a rear bed unit
This is really a Jackson center service inquiry because the thermostat is typically zone 1 and would be use for the single AC. But the fact that the remote sensor is hooked up at all.....makes me gun shy to say just disconnect it.

The post by lento above shows that they want to measure the largest area....so maybe that is why it is setup the way it is. It may revert from remote to local sensor it if it disconnected....but then the whole trailer is being calculated from the thermostat area not the remote sensor.

I would really call Ohio and see what service can tell you.
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Old 04-08-2021, 01:31 PM   #17
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This is really a Jackson center service inquiry because the thermostat is typically zone 1 and would be use for the single AC. But the fact that the remote sensor is hooked up at all.....makes me gun shy to say just disconnect it.

The post by lento above shows that they want to measure the largest area....so maybe that is why it is setup the way it is. It may revert from remote to local sensor it if it disconnected....but then the whole trailer is being calculated from the thermostat area not the remote sensor.

I would really call Ohio and see what service can tell you.
Thanks. I may just try lentoís suggestion about pulling out the sensor and trying to insulate it
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Old 04-08-2021, 03:01 PM   #18
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Thanks. I may just try lentoís suggestion about pulling out the sensor and trying to insulate it
That is exactly what I did with my sensor also, being butted up against the wall is part of the problem, the fridge super heats the wall causing a radical offset in the proper temp reading.

Let us know how you make out.
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Old 04-08-2021, 06:15 PM   #19
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I am going to try disconnecting the rear sensor on my 26 RBT. I believe the ducted AC pretty well circulates either AC's output, so just using the main thermostat should work pretty well. Main drawback I can foresee is that if I have both ACs turned on that they will probably both try and turn compressors on at the same time, but we only do that when hooked up to 50amp service so don't see huge problem.

Note - I did discover on mine that the remote thermocouple was not the phone jack, but rather a different 2 wire connector more like a molex connector. How do you tell? When both zones read the same inside temperature. When I disconnected the phone jack (also 2 wires) I got an 'E1' error displayed for Zone 2 and the two zones displayed different inside temps.

Am going out for a two week trip next week so can test if this works if temps get warm enough.

Dave
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Old 04-11-2021, 04:45 PM   #20
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My AC is fixed and sensing the proper temperature. AS called my dealer and told them to remove the cover and pull the wire out from the wall. They then cut a piece of boot rubber to go around the wire and siliconed it to the wall. This was to insulate the wall from the sensor. Unfortunately since the sensor cover is about 1 inch in diameter the small piece of rubber wasn’t quite enough insulation. So, I removed the cover and cut a round piece of corrugated cardboard that fits tightly under the cover over the piece of rubber. I’m happy to report that the system is now working as it should. I measured the temperature at the remote sensor with a thermistor and it matches the temperature on the thermostat when the system stops running. We are at a campsite in Florida right now and it has been cycling on and off maintaining the comfort in the trailer. As far as I’m concerned the problem is solved.
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