The first step is to determine whether your heating system has a 24 or 48-volt service. You do this by checking how many wires are coming out of the socket in your wall at the end of the heating system’s supply run. If there are two wires, then you have a 48-volt system. If there are three, then you have a 24-volt system. Let’s see in detail to start heat pump thermostat wiring.
Steps to heat pump thermostat wiring
Follow the steps to heat pump thermostat wiring perfectly.
Using the fan side of your 24 or 48-volt thermostat, wire it to the common contact (the one that will be energized when the heat pump is on).
Wire the heating side to a 110-volt relay, along with the wires from both sides of the thermostat. Then connect these wires with the contact wires that will be energized by a 24-volt transformer. Connect the 110-volt relay to these wires as well.
Wire up your transformer to one of your heat pump’s power leads (the red wire) and connect this lead to a 110-volt source, such as a lamp cord plugged into an outlet.
To test it out, just make sure you have connected everything correctly and then turn on the switch that runs the fan side of your thermostat (this is usually located at or near the bottom of your thermostat). The relay should close, sending 110 volts through both sides of your thermostat. If nothing happens, then something has probably been reversed in your wiring diagram.
Assuming that your thermostat has a relay, you can wire it to the pump control circuit of your heat pump by using the same 110v relay and wiring up the 220V lead from the compressor side of your thermostat (this is usually a blue wire) with reference to the instructions in your heat pump’s manual.
Once this is done, you will need a way for your heating system’s fan switch (usually located near or at the bottom of any given unit) to energize and de-energize this relay when you want it to do so. The easiest way is to use a double pole switch and have each set of contacts connected to two wires that come out of either one side or both sides (one from each contact) of your previously wired relay.
If you want to wire it differently, then just make sure that when the fan is turned on, the contacts are connected together (in series) and when the fan is off, they are not (open circuit). This will have both contacts attached to one side of the relay, which should close it when the power comes in. Then all that’s left is wiring up this switch with a 220 V lead coming from the compressor side of your heat pump thermostat and an additional hot source directly from the phase of your home’s AC service. You can also find instructions for doing this by reading through your heating system’s manual.
With everything now working properly, you’re done! Now just set up your thermostat to turn on the heat whenever you want it on (or off) and maintain a comfortable temperature.
I hope this helps!