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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Installed a train TZEMT523AA21MA nexia thermostat and

Customer Question

installed a train TZEMT523AA21MA nexia thermostat and nothing happened. Screen didn't light up. Replacing an Emerson model which only uses 4 wires
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: Theremostat. System works fine with emerson thermo. I can't replace it with the Trane
JA: Do you plan on doing the work yourself?
Customer: Yes I did. Four color coded wires that match what they did on the emerson - followed instructions sing fault tree and pin location Red-Yellow-Green-White. Truly straight forward, but once wires connected, face plate put on and power turned on - trane unit will not power up
JA: Anything else we should know to help you best?
Customer: That it.... simple installation and good instructions. Unit wont power up when power comes back on.
Submitted: 8 months ago.
Category: HVAC
Expert:  airheatman replied 8 months ago.

A COMMON wire is necessary to power the Nexia. You do not have a common with only 4 wires. Is there an unused wire coming out of the wall in the bundle that we can use to common?

Customer: replied 8 months ago.
Probably. Just havre to locate the other end of run and connect free blue wire to grd
Expert:  airheatman replied 8 months ago.

Not to ground but to 24 volt common from transformer.

Usually there will be a C on furnace board just like thermostat.If you can give me model on furnace I will tell you where to connect it. re you there so you can verify the presence of the 5th wire now?