to operate an inline duct fan on a long run to a new addition. Thermostat in the new addition activates fan when the thermostat is set to cooling perfectly. I can use it to manually turn on the fan. But when I go to heat nothing happens and I get no voltage reading coming from the relay. I first checked the white wire for potential breaks but there was no resistance. I thought perhaps something was wrong with the control center so I swapped it out with another I had, both being new in the box. So I swapped out the thermostat with another new one. Same thing every time. I'm baffled for something that should be fairly simple. Any suggestions?