can't find C wire at thermostat

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  #1  
Old 11-01-19, 07:19 PM
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can't find C wire at thermostat

I'm about to install a smart thermostat. I removed the old thermostat cover and see 4 wires connected to the thermostat. The old thermostat is powered by two AA batteries.

Green Wire connects to G
White Wire connects to W
Black Wire connects to Y
Red Wire connects to R

The C connection is empty on the thermostat.

When I go downstairs into the basement and remove my furnace cover it appears that there is a wire connected to the C. So shouldn't this wire also be going to the thermostat? I've looked behind the old thermostat, but I don't see a 5th wire anywhere. Just a bundle of 4 wires. Am I missing something or do I have to call an HVAC technician to install a C wire? Thanks

The pictures below show the thermostat connections and the furnace circuit board.
 
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  #2  
Old 11-02-19, 01:27 PM
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Hi, the C at the furnace is probably going out to the condenser unit for your AC., unfortunately you will need to get another wire up to the Tstat, there are other ways but I believe this is the best.
Geo
 
  #3  
Old 11-03-19, 11:22 AM
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Nope.... you are seeing correct. You'll need to replace the 4 wire cable.
When doing that..... add extra conductors for future.
 
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