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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 861
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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The thm5421c goes to a unico smart control board. ran a 5

Customer Question

the thm5421c goes to a unico smart control board . ran a 5 wire to the t stat for a new Honeywell bee why fi t stat do I need to keep the thm5421c in line
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: got the call call monday
JA: Do you plan on doing the work yourself?
Customer: yes worked in the hvac sys for 20 years have to learn the new sys better
JA: Are you an HVAC professional?
Customer: I hope so
JA: Anything else we should know to help you best?
Customer: i know oil and gas sys well control are weak point need to learn more to be the best
Submitted: 6 months ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 6 months ago.

Hi I'm Brian and I'm here to help. I'm sorry your question slipped through the cracks, I saw it on the board now for the first time.

What is the model number of the new thermostat you want to use? Only certain thermostats interface with the EIM panel (THM5421C). If your new thermostat is not one of them, you will have to bypass the EIM and wire the new thermostat directly to the Smart Board. If you do that and have anything wired to the U relays on the EIM, you will lose that functionality.