Monday, October 29, 2018

Driver Operated AC/ Furnace Remote Thermostat Switch

We do use our rear Dometic AC quite often even while under way, but there are times I wish I can turn the AC on and off from the driver seat instead of yelling at the rear passengers to have them operate the Thermostat. I already have a remote generator start switch mounted on the overhead cab so adding a wired remote thermostat switch in that same location will give me total control from the driver seat. The added convenience of remotely shutting the AC and generator before pulling into a gas station, etc. is a much worth modification at least for our RV lifestyle. 
 
It is a pretty simple switch with LED indicator lights for the Fan, AC, Furnace, and Heat Strip. It cycles to different modes every time you push the momentary remote switch, it basically mimics the Dometic thermostat operation, although, I’m not able to change the temperature setting from the wired remote itself.
 
I use an Ethernet CAT cable run from the Dometic thermostat to the front cab for the remote signaling. The CAT cable 8-conductor wires were all used, 6-wires for the 5-LED indicators and 2-wires for the momentary switch. I also purchased an Ultra Thin Ethernet patch cable, the cable is cut in half, one RJ45 connector is used by the wired remote and the other is connected to the thermostat. The ultra thin cable wires make it easier to route the wires inside the thermostat and the modified wired remote box. The RJ45 connectors also make it easier to plug and unplug the remote and the thermostat for servicing.
 
Things you need:
The Dometic Single Zone Thermostat with the face cover removed. Connections are tapped before the LED resistors, this is the cathode line and it's regulated at 5-volts. The remote switch needs 5-wires for each of the 5 LED cathodes (-) and 1 -wire for the anode (+) connection. The remaining two wires taps into the momentary switch.
 
Here is the finished wired remote Thermostat Switch. The On/Off LED light is built in into the momentary switch. You need resistors in series with the LED's to limit the current. Resistor value depends on the LED spec. LED resistor calculator can be found here: Click here. I ended up using higher value resistors as the LED's were too bright.
 
The remote housing is a small Ethernet junction box spray painted black. The labels are dry transfer decals sealed with clear Polyurethane spray for an OEM look.
 
One of the RJ45 Keystone Module Connector.
 
Wired remote Thermostat Switch mounted to driver side overhead cab.
 
With the AC switched on.
 
With the furnace switched on. That's it, happy Trekking to all! 
 
 

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