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jack b
Gone Fishing
Premium,MVM
join:2000-09-08
Cape Cod
kudos:1
reply to PhoenixDown

Re: Nest & Tracking Heating Effeciency

The only way you could use your Nest or any other low-voltage thermostat to control a room AC is to hook up a suitable load-rated relay inline with the unit's power supply outlet.

This is doable, but the main key to it's success or failure is if the AC unit itself resumes cooling at IT'S setpoint, after line voltage is interrupted and restored.

A lot of AC units will not even restart automatically after a "power failure" or will run cooling @ 76 degrees, or such.

For a remote thermostat to do the job, you would need to set the unit as low as it goes and allow the remote stat to cycle it on and off.

I've done this setup before and it can work!
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TheMG
Premium
join:2007-09-04
Canada
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Reviews:
·NorthWest Tel
said by jack b:

The only way you could use your Nest or any other low-voltage thermostat to control a room AC is to hook up a suitable load-rated relay inline with the unit's power supply outlet.

You're right, getting such a thing to work well with a modern electronically-controlled A/C unit can be a big pain.

I've run into this before. At work we had an A/C unit replaced at one of our sites where the A/C unit was being controlled with a contactor as part of a more complex HVAC system. The new unit has electronic controls, and would default to "OFF" after power is removed from it.

We actually had to get a firmware modification from the manufacturer of the A/C unit to resolve that problem.