Advice/Help w/ Coil Fan Thermostat
I'm trying to replace an extremely old line voltage (120v) 4-pipe coil fan thermostat in my condo with a new digital one. When I removed the old thermostat from the junction box, I noticed there were 4 wires. Since this is a 4-pipe system, two of the wires (red and blue) are for heating and cooling respectively. The white wire is line and the black wire is apparently for the fan. There is no neutral wire. I looked at the junction box attached to the Fan and confirmed there were only 4 wires in the armored cable and none of them were connected to neutral. The new thermostat I got requires a neutral connection to operate.
Is there any way I can work around this, or do I have no choice but to get new armored cable routed between the fan and the thermostat? (Or settle with a old-style analog thermostat?)
Picture of junction box on fan system. Going clockwise from the left, you see the connection to the cooling line, the fan, the heating line, and lastly the connection going to the breaker (top white and black line) and below that the 4 lines that go to the junction box where the thermostat goes.
Any help/advice would be appreciated.
Posted Jul 26, 2015, 10:05 PM UTC
The best way would be to get a new cable up to your thermostat box. The only other solution I can think of would be to tie the fan into the heat/cool wires via several relays. This would free up the 4th wire to be used as a neutral. The downside is that you would not be able to run the fan by itself, it would only run when there is a call for heat or cool.
I guess I'll be calling an electrician tomorrow. Out of curiosity how would the relays thing work?
You would need two relays, each with a 120 volt coil. One relay coil would be hooked up to heat, and the other to cool. You would then run power, in parallel, to a normally open contact on each relay. The two switch legs from the relay contacts would then be tied into the hot wire going to the fan.
For manual fan operation OP could add a manual on/off switch. Unusual to do that with these though AFAIK.