Hunter 42999B Digital RV Thermostat Install

Our Keystone Cougar 276RLSWE Fifth Wheel came equipped with a Coleman-Mach Analog Thermostat to control temperature when using either the Airxcel Air Conditioning or the Suburban LP Gas Furnace.

I noticed a problem right away with trying to maintain a comfortable temperature in the rig. It seemed like there were large swings in temperature between the furnace or the AC on and off cycles. Also with the analog type slider knob it was hard to precisely adjust the temperature.

Coleman-Mach OEM

I did a little research on the web and found many people had upgraded to a digital type thermostat and were happy with the results. Most of the articles recommended using the Hunter brand Model 42999B, as it was capable of controlling the cooling and heating, plus the fan function. I was able to find one in a local hardware store. They are available here at Amazon as well.

Hunter RV Thermostat Model 42999b - Open

To get the same hi/lo fan functionality as the Coleman-Mach analog model I needed to do a slight modification to the wiring by installing a 2-way toggle switch in the fan circuit. It’s a very simple hook-up, but solder is recommended to create reliable connections.

Hunter RV Thermostat Model 42999b - Fan Switch

Mounting the unit is no problem, just take off the OEM thermostat and use the existing hole and wires. These are the colors used in my Keystone Cougar. I imagine they are pretty standard in the RV industry but don’t take it for granted. Try to see what if the colors are the same on your OEM thermostat before you unhook everything.

· Red – 12 volt DC power

· Yellow – Controls the Cooling

· White – Controls the Heating

· Green – Fan Hi/Lo

· Gray – Fan Hi/Lo

On my install, I attached the gray and green wires to the outside switch toggle terminals and ran a blue wire to the fan control terminal.

Hunter RV Thermostat Model 42999b - Hookup Wires

There are a few things to program on the Hunter 42999B Digital RV Thermostat to get things setup the way you like. On the control board, there are option switches for Celsius / Fahrenheit and another for using the unit with an LP Gas or Electric type furnace. Also, you need to program in the span setting. This tells the thermostat when to come on and turn off. I set mine up for +- 1 degree to get the most even heating and cooling temperatures. All the settings can be found in the owner’s manual located on the Hunter website.

I’ll add my recommendation to the others I had found; this is a great inexpensive little mod to increase your RV’s heating and cooling functionality. I found it a big improvement over the analog model. – Ray

Video Detailing my Hunter 42999B Digital RV Thermostat Install

Supco 43054 Electronic Digital Wall Thermostats with Blue Back Light, 45 to 95 Degree F, 20-30 VAC
Price: $29.37
You save: $4.43 (13 %)
6 new from $27.0010 used from $15.97

Update: The Hunter 42999B doesn’t seem to be available anymore, however, the Supco Thermostat 43054 is basically the same. I’ve also been informed by a reader that another workable replacement option is the Honeywell RTH52100 1025 Deluxe Thermostat. The key feature it has is to automatically switch from cooling to heating mode. – Ray

See more interesting RV mods and Upgrades in the Love Your RV! Archives

Hunter 42999B Digital RV Thermostat Upgrade | Love Your RV! blog -

Share this post with other RVers, thanks!
  • Bob S

    Hi, I have a couple comments.
    – The Hi/Lo Fan switch that Ray recommends works fine, but it is a three position switch. You would end up with Hi/Off/Lo. So, you could inadvertently set the the Fan to Off when the air conditioning compressor is running. I used a two position SPDT switch, so Hi & Lo are the only possibilities. The switch is available here
    – I have a DuoTherm airconditioner so I had to make two changes to the wiring. I had to connect the GND wire to the RC/RH contact instead of the power wire. Also, for Hi Fan the Hi & Lo Fan wires had to be connected together.
    – This tip is great! I had no idea I could replace my RV thermostat with a modern digital home thermostat.
    Many thanks to Ray!
    Bob S

    • Thanks for the comment Bob, I never noticed I linked to the wrong type of switch. I’ve updated the post. Cheers Ray

  • terry

    Hellp Ray
    Here is what I found and did.
    My thermostat wire were white, red, blue, green so it didn’t match. I removed air box cover and found:
    white on GL===low fan
    green on GH==-high fan
    Red on yellow=yellow
    blue on B-
    So I wire to thermostate
    White & green to hi/low fan
    red on yellow
    blue not used
    red on RC
    jumper between RC & RH
    white on white
    All works well. Sorry to have bothered you. Thank you for ALL the information on you web sites.

  • terry

    Sorry Ray, I’m back
    One set of wires red and white. I guess these to be heater and red to RH and white to W pole.
    Other set of wires red, white, green & blue. If this is a/c I guess the red goes to RC and 1 to compressor other 2 are hi/low fan. With no red jumper needed. When it stops rainning I plan on taking shroud off a/c and try the chase wire, hope the colors stay the same.
    I am trying to do the exact swap you did. I have a 2012 Keystone Avalanche 330RE with 15K unit. HELP

    • Hey Terry, I have real weak internet right now, will check into it Tommorrow. 🙂

  • Terry

    OK Ray after watching the tutorial I’ll take the red jumper wire out and put red hearter on the RH pole and the red a/c wire on the RC pole. Please just confirm this is correct. Thanks Ray.

  • Terry

    OK I have a slight porblem. I have two red wires. I have 2 wire sets. One has 2 wires red & white, I figure its the heater. And a another set of 4 wire red, yellow, green & gray. So green and gray are fan yellow cooling. What is this red wire. Do I just put the reds together? I am trying to replace the same units in the pictures.

  • Hi there! Thank you for this tutorial. I was wondering if you knew if I could simply use a Honeyville thermostat and tape off the gray wire (since I don’t care too much about fan function)? There is a spot for the green still so would I simply get high fan but not low fan? Thanks for your help.

    • Yes, the Green and Gray are the two speeds, if you only want one speed you can do away with the switch and tape off the unused wire.

  • Frank D

    Here is a pdf file I created using a LUX DMH110a non-programable digital thermostat for my Heartland North Trail travel trailer. Some info is trailer specific, but all info is usable no matter what type of RV you install this thermostat into. This product has Lux Thermostat company support where hunter doesn’t.

    • Thanks for the great info Frank. The Hunter model is getting harder and harder to find so this is timely.

  • Thomas

    check the price. How could this be $25000.00 for hunter 42999b. Fix the price.