Filter
Top Products
Digital Thermostat Installation in RV HVAC Systems
Page 1 of 5
Coleman Mach to Hunter Digital Thermostat Instructions
Credit given where credit is due: This page written by Ken Lenger and derived from the text
from Alan Paskey and Les Adams. Credit for the original concept and details of the Coleman
modification is given to Alan Paskey. Les Adams further developed this concept to work with
the Dometic A/C and Atwood furnace. Their comments follow page 2.
The Coleman Mach analog RV thermostat can be replaced with a Digital Hunter thermostat part
number 42999(B) or 42995 to provide tighter temperature control in both heating and cooling
modes. The hysterisis program for the Hunter thermostat is +/-1 degree of set temperature, and
also provides a digital readout of ambient temperature. The Hunter unit can be purchased from
Wal*Mart for about $20. I have also verified that this mod will work with the Lux TX500
thermostat, which is available at many hardware stores.
Although the Hunter thermostat is designed to work with mili-volt and 24 vac residential HVAC
systems, it can be used in an RV DC system because the thermostat uses battery power to run
all of the thermostat electronics, which in turn controls internal relays to run the heating and air-
conditioning equipment.
Function
Coleman Mach
Wire Color
Hunter P/N 42999 or 42995
Terminal Designation
+12 VDC Power Red RH and RC (Note 1)
DC Ground Blue Not Connected (Note 2)
Furnace (+12 VDC switched) White W
Fan High (+12 VDC switched) Green G (see Note 3)
Fan Low (+12 VDC switched) Gray G (see Note 3)
A/C Comp (+12 VDC switched) Yellow Y
Note 1: The +12 VDC wire is required because the Hunter thermostat switches this power
through switches and relays to operate the HVAC equipment. The RH terminal supplies power
to the heating equipment and the RC terminal supplies power to the air conditioning equipment.
Note 2: The DC ground wire is not used. On the Coleman Mach thermostat, power to operate
the electronics is derived from RV +12 VDC power. The +12 VDC power and DC ground were
required for this. Since the Hunter thermostat uses battery power to operate it’s electronics, the
DC ground wire is not required.
Note 3: There are three options for the fan control terminal wiring:
Option 1: The G terminal can be connected to the green wire removed from the Coleman
thermostat for manual high speed fan operation, or to the gray wire for low speed fan operation.
Option 2: The G terminal can be connected through a SPDT switch to select either high or low
speed.
Option 3: The G terminal can be connected through a relay so that the fan runs on low speed
whenever the fan is turned on with the FAN switch on the T-stat (G terminal), and runs at high
speed whenever the A/C compressor is running (Y terminal). This option allows you to run the
fan at low speed to circulate air, but still have the A/C run at maximum capacity when on.
Note 4: The HG / HE switch in the T-stat should be left in the HG position. In the HG (heat-gas)
position, the furnace fan is controlled by the furnace electronics. In the HE (heat-electric)
position, the Hunter thermostat controls the furnace fan independently of the furnace burner.
This document can be found at http://www.klenger.net/arctic-fox/hunter-tstat/