Mystery Circuit - Between Air Handler And Thermostat. What Could It Be??? - HVAC - DIY Chatroom Home Improvement Forum

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Old 06-09-2012, 08:59 AM   #1
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Mystery circuit - between air handler and thermostat. What could it be???

I'm trying to come up with some possible theories of what kind of circuits could exist between a thermostat wire and air handler??

- forced air electric, 2 zones
- Zone 1 is main house
- Zone 2 is wing of house controlled by a separate thermostat that actuates a damper to redirect air handler output to that wing of the house.

Zone 2 works fine, but when tracing the thermostat wiring for Zone 1 there appears to be some kind of circuit in the thermostat wiring somewhere well outside of the air handler. Whatever this circuit is, it's not easily accessible/identifiable. The thermostat wiring runs right alongside zone 1's hot air outlet duct.

(ie With Zone 1 thermostat wiring disconnected at AH and Thermo I measure 2 ohms red to red but 185 ohms white to white. That suggest possibly a relay coil???)

What possible circuits could be in line between a thermostat and air handler. Maybe a second damper?? What else is common??



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Old 06-09-2012, 10:09 PM   #2
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The only thing I could think of would be an additional damper. That's very normal in a two zone system so that either zone can call for heat/air while the other one is satisfied.


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Old 06-10-2012, 06:36 AM   #3
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Probably a zone panel.
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