The Homemade Heat Pump Manifesto

[jeff5may]

Originally Posted by nokiasixteth

I think i will try number 2. Or 1 with the wires. I have a workin knowledge of wires and eletrical . When it comes to this hvac stuff . I dont have a clue.
Maybe a snap disk switch on that coil that would keep it from freezin up ?

If you have a unit with an electric temp sensor, the control (pushbutton) is not just a thermostat. It is also a fan control and can do many other things depending on the model. Some analysis and reverse-engineering must happen before you can assume control of what's built into the unit. That being said, you can usually move the temp sensor so that it faces indoors and just set the unit as cold as it will go. If you're lucky, you can unplug the unit, plug it back in, and it will resume what it was doing before it lost power. Your mileage may vary.


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If you have a window unit with a mechanical (knob) thermostat, it is fairly easy to replace it. For instance, you could rig the unit with a SPDT heat/cool switch that would keep the built-in thermostat working as original during cooling season. Flip the switch to heat mode, and rig up a heating temp control to use during heating season. No problem, right?

Wrong.



The problem you will encounter happens this time of year, when you need heat the most. When the outdoor temps are above, say 40 DegF, the unit will belt out the heat nonstop. My 12000 BTU (1 ton) unit uses around 1000 watts wall power and pushes 2000 watts of heat (or more) indoors at this temp. But as the temps drop closer to freezing, the outdoor coil will freeze up and kill the heat-moving ability of the unit. Without a way to remove the frost from the outdoor coil, all you can do is shut off the compressor and hope the frost will melt on its own. If it won't, you're finished until it warms up outside.



The "snap disc" or "klixon" switch method will work as an outdoor temp sensor to tell the unit when it is too cold to run without frosting up. But to use it in a defrost control, it needs to be put on a timer to avoid short-cycling your unit to death.