No power to thermostat

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Old 05-18-14, 03:29 PM
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No power to thermostat

My thermostat is not getting power. I am attempting to locate and replace the 3 amp fuse at the air handler but cannot find it. Attached is a photo of the circuit board at the air handler (Goodman). Any suggestions?

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Old 05-18-14, 04:32 PM
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Not all systems have a fuse for the transformer. Have you located the transformer and checked to see if it's powered and working (120VAC on input, 24VAC on output)? When you said that there is no voltage at the thermostat, were you checking between terminals R and C?
 
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Old 05-18-14, 04:58 PM
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Yes, I located the transformer and confirmed 120 VAC on input and 24 VAC on output. I did not check between terminals R and C -- I switched out the original thermostat (in guest room) with another functioning one (in hallway) in the house. The original worked at its new location in the hallway, while the functioning one failed to get power when wired into the guest room location. Thank you for your response and any additional suggestions you might have. Your response leads me to believe you're well above my skill level, so I appreciate it,
 
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Old 05-18-14, 05:06 PM
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Are they 4 wires T-stat or 5 wires T-stat ??
 
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Old 05-18-14, 05:07 PM
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What makes you say that you're not getting power at the thermostat? It appears that you haven't checked to see if there is voltage at the thermostat. What happens when the thermostat calls for cooling? Does the air handler (blower) turn on and blow air? Does the outside unit (compressor & condenser) turn on? There is a condenser fan that is visible from the top of the outside unit. Is that running when the thermostat calls for cooling?
 
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Old 05-18-14, 05:28 PM
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5-wire t-stat.

I just checked for voltage at the thermostat (between R and C) with negative results. The thermostat is not powering on at all, so the thermostat is not calling for cooling. At the air handler itself, I am able to power on the fan by pressing the contactor.

Thanks again...
 
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Old 05-18-14, 05:38 PM
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Do you have a float switch in the condensate pan? Some systems have a safety switch (float) that shuts off the A/C should the condensate not drain and back up, filling the pan. Check to see if you have a float switch and if your pan is full. If that's not the problem, check to see if you have a broken thermostat wire. You should be able to check out the wiring to see if there's an open.
 
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Old 05-18-14, 07:18 PM
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I just checked for voltage at the thermostat (between R and C) with negative results.
Now check the same terminals at the control board.
 
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