Hunter 42999B Digital RV Thermostat Install

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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

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 RTH5100 1025 Deluxe Thermostat. The key feature it has is to automatically switch from cooling to heating mode. – Ray

Update July 2019Detailed installation post and video of the Honeywell RTH5100 thermostat

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

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

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