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Mod #37: Digital Thermostat

Posted By Mark Corgan On July 14, 2008 @ 5:56 am In cooling, heating | 126 Comments

The standard analog thermostat found in most RVs doesn’t control the A/C and furnace with much accuracy. The “set” temperature is not always the temperature the thermostat cycles, which results in as much as a +/- 5°F temperature change before the A/C or furnace cycles on or off. This is known as the hysteresis of the thermostat. For example, if you have the furnace set at 72°F, this could mean the temperature would fall to 67°F before cycling on and rise to 77°F before cycling off! These temperature swings aren’t very comfortable so what to do? The digital thermostat mod of course.

Mod Difficulty:

Analog thermostats have what’s called a mechanical heat anticipator, which essentially tells the thermostat when to cycle. Some anticipators are more accurate than others but for the most part are not very good at controlling temperatures accurately. The digital thermostat is much better at temperature control since it controls its hysteresis using electronics to within +/- 1°F degree of accuracy.

This mod is commonly performed using the Hunter brand residential thermostat. It’s cheap and very straightforward to install. Other residential thermostats can be used but this one seems to be the most popular. Just be sure the thermostat you select is battery powered. Some residential thermostats use 24 VAC to power them. But if they have the battery backup feature, they can be used for RV 12-volt systems.

The wiring diagram above assumes you have a Dometic A/C unit and an Atwood furnace. Other combinations such as a Coleman Mach A/C unit and a Suburban furnace are very similar so be sure to consult your A/C and furnace manuals to ensure correct wiring. See the resources below for some really nice write-ups by fellow RVers who have performed installations with various A/C-furnace combinations.

ModMyRV recommends these parts for this mod:

General Reference
Hunter Digital Thermostat Installation
Coleman Mach to Hunter Digital Thermostat Instructions

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