My 2nd floor radiant heat developed an irreparable leak, so I installed a hydronic coil on my Spacepak air handler. The thermostat will turn on the water pump, but not the fan. I switched the thermostat to cooling, and the AC works fine, so I know the fan works. Now, how do I get the thermostat to turn on both the water pump and the fan for the heating? My water pump has white connected to W, and red connected to RH. My AC has blue connected to Y, green connected to G, and red connected to RC. Will a jumper from RC to RH turn on the fan for heat? Also, my t-stat is an Aprilaire 8363.
How to get the blower motor to turn on with the new hydronic coil heat
hvacthermostat
Related Solutions
Your original wiring looked like this, where the top circles represent the thermostat terminals and the bottom the furnace.
To properly pull off the "G wire trick", you have to locate the transformer in the furnace. You then have to determine which leg feeds R, and which does not. The leg that does not feed R, will be where you connect your new C wire.
Once you have all that hooked up, then you'll install a jumper between the Y and G terminals in the furnace.
Once all that is completed, you'll have to make sure the motor is spinning at the correct speed when in cooling mode. If it's not, you'll end up with inefficient cooling. Which can cause poor performance, and/or damage to the system.
The first thing to do is check the two wires on the outside unit when the thermostat is calling for cooling. In your picture it looks like the Blue and Yellow thermostat wires are being used. You should have 24v AC across those two wires, which would normally close the 240v relay and start up the compressor and cooling fan.
If you're not getting 24v on the two thermostat wires, there's probably a bad connection somewhere. Since the air handler is working and the thermostat has power, the 24v transformer is working.
If you are getting 24v, then you can move on to diagnosing just the compressor. There are limit switches that can prevent the compressor from turning on if the coolant level is off. There can also be temperature sensors that prevent the compressor from running, so these would need to be checked. The relay should also snap shut when the 24v signal is present. A poor connection might read 24v, but might not have the amperage to actually close the relay. The relay can be corroded or filled with dead ant bodies.
I hope this helps. Clarify anything you can in the comments and I can attempt to edit as needed. I've done a lot to diagnose and solve problems with a WiFi thermostat and heat pump that were not wired correctly.
Best Answer
You need the wiring that turns on the pump to also turn on the fan. You may need to add a relay to isolate the fan from the pump due to different voltages or any other problem that could create. You could also use a temperature controller to run the fan which is how commercial installations do it. A controller like the " honeywell T675A1425" or a " White Rodgers 3F01-111 could be used, They would turn the fan on and off when hot water is present.