House has two thermostats, no idea what the one on the second floor does.?

Question

My house has two thermostats, one downstairs, one upstairs.

The one downstairs works, turns on controls the heat and A/C unit.

The one upstairs does not turn on, even when I replace the batteries.  I only have one furnace and one A/C unit.  But the thermostat downstairs has a lightswitch next to it, which I cannot figure out what it does at all.  I know it doesn't control a light or an outlet.

I know it's virtually impossible to figure out what the upstairs thermostat does (or the point of it), but any ideas?  Any thing I can test to figure it out?

Anonymous · Answer

It controls an auxiliary blower unit when the downstairs thermostat, which is the master thermostat control, has the units on. So basically if it's reading a temperature that is different from the master...... It will either turn the auxiliary unit on or may keep it off if not needed.

Spock (rhp) · Answer

when the heat/ac is running, do you get strong airflow in the registers upstairs?  if not, it is possible there's a second circulation fan in the ductwork somewhere and this thermostat turns that fan on and off as temperature changes relative to the target temperature you've set.  it likely wouldn't turn the whole system on and off ... just the circulation fan for the upstairs

mustanger · Answer

Since it's a two story perhaps it had Two units at one time thus two thermostats. My daughter's two story had separate units and thermostats for up and down stairs.

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House has two thermostats, no idea what the one on the second floor does.?

3 Answers