Modification to RV Digital Thermostat to Raise and Lower Set Point Remotely

This is a modification to a residential thermostat used for an Recreation Vehicle (RV) that allows wireless adjustment of the temperature set point using off the self components. Its intended as a convenience modification so that you can raise or lower the set temperature from anywhere in the RV.

The modification can be done to many types of non programable types of battery operated residential Thermostats but only the module used in this procedure is detailed. You will need to pay attention to the common wiring in Step 3 to wire up a different Thermostat.

The Wireless Relay board used her has two remoted with two push button switches and an internal battery (this may need occasional replacement). The A and B buttons are intended to RAISE and LOWER the temperature setting.

You will need the following tools / equipment:

1) Solder Iron (for electronic components)

2) Resin core Solder

3) Isopropanol Alcohol

4) Small Phillips Screw driver or screw driver set

5) Ruler or Tape measure

6) Volt / Ohm Meter

6) Safety Glasses

7) Magnifying eyewear (optional - for older people like me!)

You will also need the following parts:

Parts List:

Item Cost     

1ea Digital Thermostat                   $27.99

1ea Wireless Relay Board & Remote $16.19

1ea Voltage Regulator (optional) $ 7.39   (for 2ea)

1ea Enclosure – your choice  $ 12.00 (or less)

(I have supplied 3D printable STL file) ---

*** see attached file 

Miscellaneous Wiring needed ---

 Total Cost: Less than $64

 NOTE: Cost are as of 1/4/2025

Thermostat modification steps:

1) Remove the four screws holding the Thermostat together (not the back mounting plate).

2) Next, Removed the four screws that mount the Printed Circuit Assembly, or PCA, so that you can solder wires onto the two Switches mounted on the PCA.

3) Choose 3 different colored wires and cut 12-15 inch lengths of each.

4) Locate the UP and DOWN switches on the front of the Thermostat PCA.

5) Using an ohm meter, determine which side of the UP and DOWN switches are common to each other (meaning the are electrically the same point).

6) Solder the 1st-colored wire to the Non Common side of the UP Switch.

7) Solder a 2nd-colored wire to the Non COMMON side of the DOWN Switch.

8) Solder the 3rd-colored wire to the COMMON side of either switch, they are the same point electrically.

9) Carefully feed these three wires to the back side of the PCA through an access hole in the PCA or the side of the PCA.

10) Re-mount the PCA to the Front Panel with the same four screws previously removed.

11) OPTIONAL: Solder a 4th-colored wire, I suggest a Green wire be used, to the Positive side of the Battery connection of the PCA.

12) OPTIONAL: Solder a 5th-colored wire, I suggest a White wire be used to the Negative side of the Battery connection of the PCA.

13) Thread these wires through the back opening of the Rear Housing of the Thermostat that was previously removed and secure the housing in place with the four removed screws. Care must be taken to ensure the wires do not get in the way of the connectors on the back of the Thermostat as these are to connect through the wall plate to connect the furnace wiring to the Thermostat.

14) These five wires will be connected to the wireless remote switch in the next section. They may go through the wall into an adjacent area or to the side of the Thermostat into a separate enclosure (see the next section).

NOTE: Steps 11 and 12 are optional if you choose to use batteries in the Thermostat.

Disconnect the Power coming to the RV and the 12 Volt Battery connection BEFORE proceeding!

Wireless Relay Board wiring steps:

1) Run the Wires coming from the modified Thermostat through an opening in the Enclosure to be used to mount the Wireless Relay Board in.

2) Mount the Wireless Relay Board in the Enclosure.

3) Feed the 3 (or 5 wires if 1 using the separate power supply) wires from the modified Thermostat over to the hole in the bottom of the Wireless Relay Enclosure.

4) Connect the wire from the “UP” switch on the Thermostat to “NO1” on the Relay Board.

5) Connect the wire from the “DOWN” switch on the Thermostat to “NO2” on the Relay Board.

6) Connect the ‘Common’ wire from the Thermostat to “C1” on the Relay Board.

7) Connect a ‘Jumper’ wire from the “C1” to “C2” on the Relay Board.

8) Mount the Enclosure near the modified Thermostat bracket.

NOTE: The Thermostat will be hanging loose at this step so be careful to not damage the wires coming from it,

The following steps are for the OPTIONAL Voltage Regulator:

NOTE: The Voltage Regulator MUST be ‘pre-set’ to regulate 12 volts DC (or VDC) down to 3 VDC prior to performing the following steps. Once the setting is made, use a small drop of fingernail polish to lock the adjustment potentiometer in place so the output voltage stays at 3 VDC. You may wish to consult a friend with electronics experience for this step if you don’t feel comfortable doing this.

1) IF using the Voltage Regulator assembly, mount it in the same Enclosure with the Wireless Relay Board.

2) Connect the Green Wire coming from the Positive Battery side of the Thermostat to the Positive Output Side of the Voltage Regulator.

3) Connect the White Wire coming from the Negative Battery side of the Thermostat to the Negative Output Side of the Voltage Regulator.

4) Connect the Positive 12 VDC to the Positive input point on the Voltage Regulator (the Red Wire on the Thermostat is usually the 12VDC).

5) Connect the Negative (or Ground) 12 VDC to the Negative input point on the Voltage Regulator (the BLUE wire spoken about earlier is usually a Ground point).

This step connects the modified Thermostat to the RV wiring and the Wireless Relay circuit in the enclosure.

Ensure the Power coming to the RV and the 12 Volt Battery connection are disconnected BEFORE proceeding!

Connect the wiring in the RV to the modified Thermostat with the following steps:

1) Connect the RED Wire from the RV to the RH/RC terminal on the Thermostat (the RH and RC Terminals should be shorted together.

2) Connect the GREEN Wire from the RV to the G terminal on the Thermostat.

3) Connect the YELLOW Wire from the RV to the Y terminal on the Thermostat.

4) Connect the WHITE Wire from the RV to the W terminal on the Thermostat.

5) Connect the BLUE Wire (IF PRESENT) from the RV to the C terminal (Common) on the Thermostat.

6) The GRAY Wire may be capped off, it will note be used. The Gray wire is the 'Slow' speed fan for the AC but most people do not use this,

7) Reconnect the RV power and 12 V battery to test the Thermostat

NOTE: If you desire to have two speeds for the AC fan you can add a double pole switch to the modification and wire a separate GREEN wire (or other color not used previously) to the center of the switch and then wire the original GREEN wire to one side of the switch and the GRAY wire to the other side of the switch. This will allow you to select between High and Low fan speeds.

Connecting the modified Thermostat to the wired mounting bracket for the Thermostat

With the Power to the RV and the 12V battery still disconnected perform the following steps:

1) Very carefully attach the Thermostat onto the wall mounted bracket so that the new wiring added goes through the wall without interfering with the Thermostat mounting. Also, take extra care to ensure the new wiring does not get in the way of mounting the Thermostat onto the bracket its self.

2) Ensure the Thermostat is set to the OFF position. Reconnect the RV power and 12 V battery to allow testing of the Thermostat.

3) Turn the Thermostat to the HEAT position and raise the set temperature with the buttons on the front of the Thermostat to the point the Heater should turns on,

4) Lower the temperature set point until the Heat turns OFF.

5) Now, use the A/B remote that came with the Wireless Relay board to try and raise and lower the set point of the Thermostat with the Remote.

6) If all steps have been done properly the Remote should be able to raise and lower the temperature set point by clicking the A and B buttons.

7) The AC (Cooling) operation can be checked in the same way by selecting the COOL setting on the Thermostat.

8) If the A button lowers the temperature and the B button raise it, just witch the wires positions on the Wireless Relay board in STEP 2, sub-steps 4 and 5, of these instructions,

Now just enjoy using the remote to raise and lower the temperature throughout you RV!