Grand Design (and other manufactures) install one or more Dometic Brisk series air conditioners in their RVs. These newer Dometic AC units utilize an "improved" Capacitive Touch (CT) control digital thermostat to manage both air conditioner cooling temperatures as well as LP furnace heating temperatures. My personal experience with these thermostats is that they are temperamental to operate (erratic controls) and do not maintain the cool or heat set temperature well. My goal was to replace the Dometic digital thermostat with a conventional residential analog thermostat.
The Dometic digital thermostat communicates with the AC control board in the roof-top unit over a simple proprietary one-wire digital bus, making it difficult to replace the digital thermostat with an analog model. I have researched the options to replace the Dometic AC unit roof-top control board with an analog compatible version, but did not find a good solution. I found many forum posts with people successfully upgrading from the old mechanical analog thermostat to the Dometic digital thermostat system by replacing the control board and thermostat as a set, but not going the other way.
In an effort to improve my furnace response, and due to the poor location by GD of the Dometic digital thermostat on the hutch wall above the furnace, I installed an additional Honeywell P/N TH5110D1006 analog thermostat on the side of the galley island and connected it to the furnace in lieu of the furnace control wires from the AC unit control board (see wiring diagram). The LP furnace is old school analog (+12 VDC to turn on the heat), so the Honeywell analog thermostat worked just fine for that, and the relocation solved the problem of heat soaking from the furnace residual heat.
What I came up with for fixing the AC side is kind of clever, if I may so so myself. There are 3 wires connecting the AC control board and the Dometic thermostat: +12 VDC power, Ground, and the digital communication bus. The key to my solution working was that the Dometic thermostat has non-volatile memory, so it remembers its previous settings after the power is removed and reapplied. If you leave your Dometic thermostat AC set to ON (Auto, High, or Low) when you shut down your RV (by turning off the battery switch), the AC will immediately start working the next time you turn on the battery switch and apply external campground power. The Dometic thermostat "wakes up" with all the previous settings. Here's the clever part. I hooked up the cooling compressor ("Y" terminal) output from the Honeywell analog thermostat and connected it to the Dometic thermostat +12 VDC power input in lieu of the +12 VDC power from the AC unit control board (Pin 3). Then I set the Dometic thermostat temperature to Cool (Auto, High, or Low as you prefer) and set the temperature to a temperature lower than I expect to use (60° for example). Next I set the Honeywell analog thermostat to COOL with the temperature set to say, 78°. The Honeywell thermostat will cycle on and off as necessary to control the temperature in the RV, and (drum roll please) the Dometic thermostat simply functions as an analog to digital converter to control the AC cooling, but has no effect on the set temperature (because it is set lower than the analog thermostat). Early testing of this modification is very positive and the Honeywell thermostat has settings to control the number of on/off cycles per hour.