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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 793
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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System (heat and AC) with a Honeywell tstat. tstat went

Customer Question

Coleman system (heat and AC) with a Honeywell tstat. tstat went dead. No power on tstat red wire. There is 24VAC at the transformer going into control board but no power to tstat.
Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
varidigm vf4-1210 control board.
Expert:  Brian HVAC Guy replied 1 year ago.

Hi I'm Brian and I'm here to help!

Typically when you have this situation, the 3 amp automotive style fuse on the control board has blown. It should be a purple fuse near the low voltage terminal strip and the white connector plugs on the board. There's also the possibility that there is a field installed safety switch that is breaking the voltage to the thermostat. The most common one being a drain overflow switch but usually these are wired just to stop the cooling from working, not to interrupt all voltage to the thermostat. I would check for both issues. The fuse, if blown, can be found at any auto parts store. It's an ATC3 fuse.

Please reply if you have further questions about this. Otherwise, please remember to rate positively (3 stars or better) before you leave! Bonuses are welcome and very appreciated!

Thank you,
Brian