Weird HVAC issue, seems related to temperature


  #1  
Old 01-17-15, 11:27 AM
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Weird HVAC issue, seems related to temperature

I have a one-unit-two-zone central HVAC system. Downstairs is zone 1, upstairs is zone 2. Each zone has its own thermostat. The zone controller model is PerfectTemp 6202 (wiring diagram is something like this: Name:  6202.jpg
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Most of time both zones work fine as expected: each zone can trigger heating independently when thermostat calls.

However, when it's cold in winter night (20F or below), sometimes the zone 2 thermostat won't trigger heating (heating sign flashes on thermostat, no response from furnace). At this time, if I turn on the zone 1 thermostat, furnace will start up and zone 1 heating will be on. After about 10 minutes, zone 2 will also start to work. After that, zone 2 will continue to work even if I turn off zone 1.

It's a bit weird as it seems sensitive to the outside temperature. Any thoughts? Thanks a lot in advance!
 
  #2  
Old 01-17-15, 11:38 AM
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I'd check for a loose W connection at zone 2 stat and zone control board.
 
 

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