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Question How to tell thermostat to use itself for temp and not thermistor?

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Neal

Staff member
RVF Administrator
Joined
Jul 27, 2019
Messages
11,480
Location
Midlothian, VA
RV Year
2017
RV Make
Newmar
RV Model
Ventana 4037
RV Length
40' 10"
Chassis
Freightliner XCR
Engine
Cummins 400 HP
TOW/TOAD
2017 Chevy Colorado
Fulltimer
No
Hating the thermistor setup for zone 1 (front) in my 2017 Newmar Ventana motorhome. I'd like to set the front Dometic A/C to use the thermostat for its temperature sensor instead of the thermistor. Anyone know how to make this change? My guess is a dip switch on the roof top unit and that's what I'll start hunting down but wanted to present the question to the forum to see if anyone knows and will report back what I find.
 
I'm not sure the attached document is for the unit I have but it came up in a google search and it seems the same. It appears the P4 wire connection is the one. Zone 1 doesn't require an internal temp sensor but anything other than zone 1 does per this doc. I want to disable the internal temp sensor and see how things work using the TSTAT as the sensor.
 

Attachments

  • dometic-penguin-ii-13-5k_9105304179_62857.pdf
    1.2 MB · Views: 8
My fear though is per the purpose of the external sensor (thermistor). The TSTAT would be fine where I am here but with it being on the wall next to the door, if I had direct sun there I'd have a problem. I don't know if there is a way to calibration thermistors, I don't see a way other than offsetting temps for the TSTAT itself, think I'll have to just life with keeping the bedroom door half closed to block the zone 1 thermistor from zone 2 temps. Will go on the roof and see what the wiring looks like and how hard it would be to try if low risk. Curiosity is all there is for now.
 
My fear though is per the purpose of the external sensor (thermistor). The TSTAT would be fine where I am here but with it being on the wall next to the door, if I had direct sun there I'd have a problem. I don't know if there is a way to calibration thermistors, I don't see a way other than offsetting temps for the TSTAT itself, think I'll have to just life with keeping the bedroom door half closed to block the zone 1 thermistor from zone 2 temps. Will go on the roof and see what the wiring looks like and how hard it would be to try if low risk. Curiosity is all there is for now.
My zone one is the Thermostat on the outside wall (I'm assuming same location as yours) and, you are right, it reads hot in most situations. I just keep zone 1 higher than the thermistor based zones (two and three).
 
Neal -
I thought about making the same adjustment but decided to take a different approach. I used a box extender (like those on GFI outlets) and drilled holes around the sides to allow for airflow. Then mounted it in place of the thermistor adding some thin foam insulation between the wall and the holes. Then mounted the thermistor on a blank plate screwed to the extender.
Now coach air flows behind/around the thermistor; seems it reads the temps closer to actual than before.
joe


8F837409-592E-4C2F-9E64-471684CDAB8D_1_201_a.jpeg
 
Neal -
I thought about making the same adjustment but decided to take a different approach. I used a box extender (like those on GFI outlets) and drilled holes around the sides to allow for airflow. Then mounted it in place of the thermistor adding some thin foam insulation between the wall and the holes. Then mounted the thermistor on a blank plate screwed to the extender.
Now coach air flows behind/around the thermistor; seems it reads the temps closer to actual than before.
joe


View attachment 14470
Interesting. Your's is a bit of a different problem than Neil with the Thermistor. His Thermistor problem is that it's located to close to Zone 2 (sill placement by Newmar, which I have as well, but with Zones 2 and 3). His and my thermistors are on inside walls.

However, it's possible the same trick you have there, but with the thermostat, instead of thermistor, might help keep the thermostat from reading so high.
 
My zone one is the Thermostat on the outside wall (I'm assuming same location as yours) and, you are right, it reads hot in most situations. I just keep zone 1 higher than the thermistor based zones (two and three).
This makes sense. My system works just fine, but both my thermistors are on interior walls. Maybe someone should mention this to Newmar.
 
Neal -
I thought about making the same adjustment but decided to take a different approach. I used a box extender (like those on GFI outlets) and drilled holes around the sides to allow for airflow. Then mounted it in place of the thermistor adding some thin foam insulation between the wall and the holes. Then mounted the thermistor on a blank plate screwed to the extender.
Now coach air flows behind/around the thermistor; seems it reads the temps closer to actual than before.
joe


View attachment 14470Reasonable solution. Makes sense to me.
 
I have the same problem. Tried insulating the sensor with foam pad. Not much difference. Finally took it off the wall and now it is hanging loose away from the wall
( I was frustrated).
.BTW I did read the install manual. Dometic explicitly instructs the sensors NOT to be installed on outside walls and no higher than 50” (I think) from the floor.
 

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