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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Trying to diagnose what's happening with my Trane XV90

Customer Question

Trying to diagnose what's happening with my Trane XV90 furnace... no heat... main blower working when thermostat fan control set to ON... furnace LEDs flash the same whether the thermostat is satisfied (not calling for heat because I turned the setting down to 58) or not satisfied (calling for heat, set desired temp to 75, thermostat says HEAT ON)
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: I turned the thermostat up to 75 to call for heat, it responded by showing "HEAT ON" and I heard the click to signal the furnace. Using an electrical multimeter at the furnace where the thermostat wires connect, I verified that the voltage from R to W1 went from ~26.5 Vac (heat off) to 0.0 Vac (heat on), so the furnace is getting the thermostat signal to engage the heat
JA: Do you plan on doing the work yourself?
Customer: Trying to see if I can at least get the heat to turn on tonight... Yes, myself, unless it just becomes a lost cause that I can't figure out...
JA: Anything else we should know to help you best?
Customer: I'm an electrical engineer with a capacity for electrical troubleshooting and mechanical whatnot, so hoping to figure out what the problem is, at least...
Submitted: 8 months ago.
Category: HVAC
Customer: replied 8 months ago.
I just power-cycled the furnace... off for 5 minutes, then back on. Zero alarm codes shown upon startup, as in, the red LED flashed once and then not again for 15 to 20 seconds. The green LED flashes about once per second no matter what.
Expert:  airheatman replied 8 months ago.

26.5v between R and W1 does not indicate we are getting signal from thermostat,Check between W and C.We may have a break in a condensate pump or float switch between thermostat and furnace.