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Mod #100: Honeywell Digital Thermostat

Posted By ModMyRV On January 3, 2012 @ 9:59 am In cooling, heating | 43 Comments

This modification was designed and completed by ModMyRV member Lencactustwo. Credit given to Ken Lenger, Alan Paskey and Les Adams for their detailed instructions with their A/C, furnace and digital thermostats. Mine is like all others, slightly different with different wire colors and a Honeywell 5+2 digital. This article carries a copyright. Permission must be obtained from the author before duplication or reposting.

I purchased my unit at the HD for $25 and have seen same at Wally and Lowes for about the same. The switch I found at Radio Shack SPDT (single pole double terminal) but found out I just needed a switch SPST (on /off) for $3.50 as did Les Adams. A little tricky notch in the bottom right corner of the base and back panel to fit. I would do it again but on the left side due to projections on the back of the circuit board.

Mod Difficulty:

My wiring was as follows: yellow wire (always A/C) to Y. White wire to W (for the furnace). Basically all furnace wiring is power wire to white, touch your power wire to the white and presto the furnace starts and cycle thru for about a minute (hint- twist them together to keep you and your loved ones warm while you figure out what else to do) (another hint- twist the yellow and your power wire together to keep you cool headed instead of the furnace).

If you twisted the red wire (typical power) to the yellow or white wire and it did NOT start the A/C or furnace, then try either of them on all other wires until it does. THAT wire is the powered wire and will go on to the R or RC terminal. My case it was the green wire to R/RC with jumper in (u shaped wire between R and RC [furnace and cooling circuits]) Now both A/C and furnace have power when the switch on the bottom is on heat(R/RH) or cooling (RC). Brown wire to G (which runs the A/C fan).

NOW for the tricky part: ALSO put one side of the Radio Shack SPST (on/ off) switch wire into the G terminal and the other to the blue (high fan speed) wire. It works like a tri light bulb 50/100/150 watts, you need 50watt on and 100watt on to get to 150watt, so both wires are powered by the G terminal to get high fan speed, see diagram below that I modified from a Hunter diagram

Don’t worry about the red wire not hooking up, you probably found out it had no power on it, and as the other gentlemen installers noted DO NOT CUT the red wire short as you may need the wire one day for future mods or the buyer of your rig when you sell it down the road may want the old thermostat re-installed.

Remember both the Honeywell and Hunter thermostat instructions were designed for home use not RV use. I have personally installed them in homes and they are exactly as laid out in the instructions: red for power, white for heat, yellow for A/C and green for fan, EASY PEZZY. Us RVers have to follow other instructions!! You know, if they sold one to work in our rigs, it would be 3-4 times the price!

Follow any of the great mods for this UPGRADE to enjoy constant temperatures in your rig so you don’t have to hear “I’m cold…I’m hot”. YES it runs MORE often, but for SHORTER times and more accurately as you can see the digital readout in 1 degree increments, not “kinda between 10 and 20, half way, somewhere, maybe 17 ¼ degrees?” Press either the up/down arrow ONCE to light up the display without disturbing the program and press AGAIN while lit up to change settings for temporary comfort relief (2 hours) or touch RUN to go back to the scheduled settings at any time.

Set up the program in BOTH the heat mode AND cooling mode even if you may not know what you may need exactly, you can always change it. A few degrees different during the night or when you are not in the rig can save you enough to pay for the new thermostat. Save the instruction book for future adjustments. As we are full timers now, I set the weekday program to be the same as the weekend.

ModMyRV recommends these parts for this mod:

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