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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 945
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: 2 years ago.
Category: HVAC
Customer: replied 2 years ago.
varidigm vf4-1210 control board.
Expert:  Brian HVAC Guy replied 2 years 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.

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