The installation of the Honeywell RTH8500D 7 Day Touchscreen Programmable Thermostat to a 24 volt standard heating and or cooling system is straight forward if the instructions are followed carefully. Although I’m going to explain in this article how it is done, it cannot be stressed enough that you should read the instruction manual provided with the Honeywell RTH8500D before you begin installation.
Before you begin gather up the tools you will need: a hammer, pencils, 3 triple ‘A’ alkaline batteries, a number 2 Phillips screwdriver, a normal screwdriver, electrical wire, sticky tabs (should be included with the Honeywell RTH8500D), a drill and suitable drill bit (3/16 inch for a dry wall and 7/32 inch for plaster).
Now you are ready to begin. First turn off the HVAC systems at the circuit breaker then remove the old thermostat from its wall plate. Do not remove the wires. It is important to remember to not follow the colors on the wires but instead use the old thermostat to correctly identify the wires.
The first thing to check is the C and or C1 wires. If there are 2 C or C1 wires then do not connect them to the Honeywell RTH8500D. instead wrap electrical wire around the bare wires. If there is only 1 C or C1 wire going to the old thermostat then use a sticky label to mark this wire as C. If there are any unused wires then again cover the ends in electrical wire. These wires will not be used in the installation.
Now you can take a wire at a time and follow it to the terminal on the old thermostat to identity each wire. Once the wire is identified then use a sticky label on the wire so you won’t forget where it is meant to go. Then disconnect from the old thermostat and wrap the wire end around a pencil to stop it falling back into the wall gap.
Here is a guide to wire labeling:
RC or R to RC
R, RH, 4 or V to R
W, W1 or H to W
Y, Y1 or M to Y
G or F to G
C, C1, X or B to C
Y2 to Y2
W2 to W2
Once you have all the wires labeled correctly and disconnected then unscrew the old wall plate and take the Honeywell RTH8500D wall plate and thread the wires through the center. Then take a pencil and mark the drill holes. Next take away the wall plate and drill holes with the correct drill bit (3/16 inches for drywall and 7/32 inches for plaster).
Once done, put wall anchors in the 2 holes and tap them in with a hammer. Then thread the wires through the new wall plate and screw the wall plate to the wall. After, you can use the labeled wires to attach the wires to the correct terminals on the Honeywell RTH8500D.
Now you are nearly finished. Put the 3 triple ‘A’ alkaline batteries into the Honeywell RTH8500D programmable thermostat and find a tab in the lower left corner that says ‘Remove during installation’. Remove the tab and push the thermostat onto the wall plate until the thermostat snaps into place.
Finally, turn the HVAC power back on and set the calendar, time and system type using the large touchscreen interface and you are ready to start putting in your program settings for each day of the week.
If you encounter any problems first consult the instruction manual again and then call the Honeywell helpline.