I have connected a W200 thermostat to my HEIL furnace but am unable to turn on the fan. I have confirmed the thermostat is sending a signal but it does not activate the fan. The blower will run when I jumper from R to G and the furnace operates correctly with my old Honeywell thermostat.
When I contacted Aqara technical
support, they suggested adding an isolation relay to my G wire. Does anyone have any idea on what I should be using for the relay? I don’t want to fry either the W200 or the furnace control board. Information I am looking for:
- Required coil voltage (I assume24 VAC?)
- Maximum allowable coil current for the W200 G output
- Whether a standard normally-open dry-contact relay is appropriate
- Any recommended wiring diagram or installation instructions
Furnace is a Heil G9MVE0601714A1
@alexpelzel Hi there! Thanks for sharing this detailed troubleshooting scenario. It’s always helpful to see how different HVAC setups interact with smart thermostats, and your question about isolation relays is a smart precaution to protect both your W200 and your furnace control board.
Based on the reference information, the Aqara Thermostat Hub W200 is designed for 24VAC systems and supports a maximum current of 2.5A. Since you are dealing with a standard gas furnace where the G wire controls the fan, using an external relay is a common solution when direct control causes issues or if the load is ambiguous.
Here is some guidance based on your specific questions:
- Coil Voltage: Yes, for standard residential HVAC systems like your Heil furnace, a 24 VAC coil relay is the standard choice and matches the W200’s operating voltage.
- Current & Dry-Contact: A standard normally-open (NO) dry-contact relay is indeed appropriate. The W200’s G terminal will switch the relay coil, and the relay’s dry contacts will then handle the switching of the fan circuit, providing the isolation you need. Since the W200 supports up to 2.5A, you just need to ensure the relay contacts are rated for your fan motor’s inrush and running current (which is typically well within standard relay limits for a single fan).
- Wiring Diagram: You can use a wiring method similar to the “Wet contact mode” described for Aqara relays, where the relay acts as the switch. The W200 G wire would connect to the relay coil (along with C or R for power, depending on the relay type), and the relay’s NO contacts would be wired in series with the furnace’s G terminal and the common/neutral side of the fan circuit.
Important Note:
This information comes from community discussions and user experience summaries and may vary by environment. Please verify carefully.
If you need specific part recommendations or further assistance with the wiring diagram, I’d recommend reaching out to the support team directly for the most tailored advice.
Contact the Aqara Home App Customer Service Team (Profile> Help & Feedback > Customer Service) or scan the QR code:
This will be more efficient. If you do not have an Aqara Home account, “Please
click here” to create a ticket.
