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I need to disable my thermostat from turning on the AC. Yes, covertly. I think one of my housemates is missing his native Antarctica. So, the thermostat still must be active & setable, but I want to disconnect the wire that controls the AC unit. I suppose the first question is: is this possible? If so, how?

The thermostat is a White-Rodgers 1F89-273. The current wiring configuration is:

  • C - Blue
  • R - Red
  • G - Green
  • O/B - Orange
  • X - Yellow
  • W2 - White + 2nd white wire connected to...
  • E - White, connected to W2
  • L - No wire connected
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2 Answers 2

It's going to be the Yellow wire that calls for cooling (surprised that's an X and not a Y).

Two things to be careful of. First, the O/B is for the heat pump valve (switching the compressor from heating and cooling modes), so I'm not familiar enough with heat pumps to know if activating this valve but not the pump itself could damage anything. I don't see why it would, but it's something to consider.

Second, if you are running an AC when it's below 60F, you run the risk of freezing the coils (literally, the whole thing could be covered in ice if it's running at this temperature). Ice on these parts can cause permanent damage, in addition to being a waste of electricity since air isn't going to pass through a block of ice. If your roommate still thinks this is a good idea, now may be a good time for them to sign a liability waver to cover the cost of replacing the AC if it becomes damaged, and to switch the electric bill into their name.

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Does O/B need to stay connected? Could not the heat pump valve be switched to heating mode, and then the wire be disconnected? Would it then stay in the proper mode? Thank you for the excellent and well-considered answer. –  John Nov 18 '11 at 6:07
    
@John Odds are good that O/B is energized to set the valve in cooling mode since it's orange, but on some models, it could be the reverse, energize to heat. O is one direction, B is often the other, so having both labels makes it a bit ambiguous. –  BMitch Nov 18 '11 at 11:31
    
If your thermostat has a battery and can operate without being attached to the wall, you could use a tester on the disconnected thermostat. See if there's continuity between R and O/B for heating or cooling. If there's a connection while cooling and not for heating, then you can leave this wire disconnected as well. –  BMitch Nov 18 '11 at 11:35
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Rather than messing with the wiring, why not install a locking thermostat cover like this enter image description here.

Just don't give your roommate a key, until they can be more responsible.

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Assuming his roommate pays rent and utilities as well, he's also entitled to change the thermostat. There is nothing irresponsible about adjusting the thermostat to a comfortable temperature. –  Zach Dec 9 '11 at 17:37
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