I have an electric furnace Carrier model FB4ANF030. I enclosed the wiring diagram.

Issue: The blower fan will not turn on automatically when the thermostat is set to "Emergency heat" and "Fan Auto".

Details: Lately, when I set the thermostat to "Emergency heat" (so that the heat pump will not be used, the heat is then provided by the internal heat coils), and set the fan on "Auto", the blower motor will not turn on when the thermostat kicks in. If I set the fan to "On", the heater works. Moreover, if I manually start the blower and then set it back to "auto" once it has started, it will keep on blowing and shut off upon thermostat command normally. The blower will not, however, start by itself on the next cycle. This results in the house cooling down (of course). When I set the thermostat to "Heat", everything is normal. (I.E. both the heat pump and the blower kick in in auto mode when prompted by the thermostat.)

Help requested: This is where I need advice from someone who can read a furnace wiring diagram. I can't seem to figure out which component is at fault.

Thank you for your help!

Pierreenter image description here

  • Hello, and welcome to Home Improvement. Did this used to work? If so, is there anything that accompanied or might have triggered the change? – Daniel Griscom Jan 13 '19 at 19:46
  • Check all of the wiring from the thermostat connections (tight, clean, etc), also check the connections (plugs/receptacles) for any molex mating connectors in the panel for the same things. Lastly, check connections and contacts of relay 2 (both legs), is it oxidized etc.. Did this used to work? – noybman Jan 13 '19 at 19:52
  • It was working fine before yesterday. I will check the connections as suggested. I highly suspect that the thermostat is the issue here. Thank you for your ideas! – Pierre-Alexandre Goulet Jan 13 '19 at 20:31
  • Quick update: I changed the thermostat for a Nest E today and everything is working properly again! Thank you everyone for sharing your knowledge! – Pierre-Alexandre Goulet Jan 15 '19 at 3:14

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