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?

  • Perhaps you have wired them incorrectly - check the diagrams again and check exactly what you have done. The last time I did something similar, I made sure of the original wiring positions with a photo and a drawn diagram. Have you checked the original wiring setup? – Solar Mike May 19 '19 at 18:32
  • No one can figure it out. I was trained in HVAC many years ago and I went over it. Two other HVAC servicemen who are friends have gone over it, and the conclusion has been forget about using the program feature of the thermostat and manually turn on the fan. Just one of those mysteries that might never be solved. – Thomas Jul 26 '19 at 17:45

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