Does such an electrical device exist

After having a really hot day today I started using my window air conditioner to cool my room down. This model does not have a thermostat you can set to a tempertaure, instead it has an colored arrow from cool to cold. Is there something I can plug in between the wall outlet (standard 3 prong plug) and the power cord that will let me set the room for a constant tempertaure by turning the ac unit on and off?

That unit must date back to the Ming dynasty but anyway, yes, you can set a thermostat in the power cord and it will work. The thermostat built in to normal units will keep the fan running but a thermostat in the power cord will stop everything. With a little ingenuity you could wire it so it would control only the compressor and keep the fan running.

I doubt an external add-on thermostat exists, but I’m unclear on what you mean by the “colored arrow”. Is it a slide type device? It could just be a lever-type switch as opposed to the rotary type you are talking about. Because as far as I know about home HVAC systems is that they all have a thermostats, otherwise the compressor would never shut off and the condenser could freeze up.

(I could be wrong, I’m just operating off of my knowledge of Automotive A/C)

I assume you mean it just has the words cool to cold rather than actual temperature numbers. It’s the exact same thing. All air conditioners have thermostats. It isn’t optional. Yours just doesn’t have numbers on the dial. Just put a thermometer in the room and you’ll figure out where on the dial is (roughly) what temp.

Also to verify the previous post, turn the knob back and forth, if it is infact a thermostat,you should hear something inside click.

External thermostat units do exist; (or they did) I’ve seen them for things like aquarium heaters and photographic chemical baths, but these aren’t going to be a suitable temperature range.

Be very careful if you go to add a thermostat. Many thermostats are made to only carry low voltage. You wire into to the 110 power and you will melt down the termostat very quickly.

try these http://www.hoptech.com/index.html?http://www.hoptech.com/tempctrl.html
http://www.tlc-direct.co.uk/Products/SMET05.html

oddly enough an animal pet shop may be a place to try as thermosatat plugs are used to control temperatures for the little critters
Biostat Thermostats http://www.bushherp.com/tempreg.html or
www.tuxford.dabsol.co.uk/sunriseaviculture/products.htm

That lever is a theromstat. To set it run it on max ‘cold’ position then when the room is cold enought slowly back the thermostat off till you hear the click (shutting off the compressor) then just slightly increase it (back to cold) but not enough to hear the click.

Take a marker or sticker or scrach a mark in that area so you know where to set it.

Really, to repeat what another poster said, the unit already has one. What you need is basically some time and a thermometer to measure what “midway between cool and cold” means on a temperature scale. Take three days or so and pick out three spots, evenly spaced, on the dial, let the AC run until it shuts off and you have (approximately) the temperature it is set for.

I guess this would be a good time to ask a related question: Why do most air conditioners have un-calibrated thermostats? Is it that much more expensive to make a calibrated one? Yes, many modern A/Cs have digital thermostats, and I can understand wanting to save costs in the low end. But I still see relatively expensive A/Cs that use the standard knob with cool/cold markings, and I can go into Home Depot and purchase a calibrated thermostat (albeit an analog one) for about $20.

In window AC’s the thermostat is next to the cooling source in a small room it would be accurate but in a larger room it would cut off the compresser before the whole room is cooled. So they just use a cool to colder scale you set where you are comfortable.

It seems a bit premature to say that just because he’s got a “cold / colder / coldest” knob that he’s got a thermostat. I’ve seen cheaper air conditioners that simply had a knob that controlled how fast they tried to crank out cold air. You set it to what you think is going to get you the right temperature room, and it just goes. Then you wake up in the middle of the night freezing your ass off. And then you never stay at the lousy courtyard inn across from the sands convention center in vegas again. :slight_smile:

Thanks for responding, but that answer doesn’t really make sense. First, you’ve got a fan circulating the air, so sooner or later the warm air from the far side of the room is going to make it over to the near side, and the thermostat would pick up the change in temperature. Secondly, if a thermostat is uncalibrated, that doesn’t make it any less of a thermostat, it just means you need to make a guess at the knob position rather than setting it at a temperature with which you are comfortable.

I think any air conditioner designed this way would freeze up in a matter of a few hours. A/Cs are not designed to have their compressors running continuously.

Use the AC’s internal thermostat.

But if you do go with the external thermostat for some reason, make sure it can handle the wattage or amperage of the AC. Some of them use quite a lot and could easily overwhelm something not designed for it.

Very True - most are for a very small current (fractions of an amp) at 12 or 24VAC. They do make bigger ones. One zone of our house has a thermostat that directly controls a 120VAC Fan.

I don’t think there’s an off-the-shelf product that directly controls the full line power (120 or 240VAC at 10-20 amps) ) of an AC.

All things considered, I’d suggest learning to find a favorite setting on the existing lever/knob/whatever.

It makes sense to me. The compressor thermostat setting that would keep a given small room at an average temp of say, 70 degrees, would only keep a given larger room down to maybe 78 degrees, since that larger room would have more heat coming into it through the walls, etc.

There is going to be a temperature gradient in the room. The larger the room, the greater the temp difference between its warmest and coolest spaces. “Sooner or later” gets to be a lot later, in practice never (in terms of the room’s average temperature being the temperature at the thermostat). In central heating and cooling systems, the thermostat can be placed in an area that would have roughly the average temperature of the room. In a window unit, there’s no choice but to have it right beside the cold air outlet, which is going to be cooler than the room’s average temp. And how much cooler will vary with room size, sun exposure, air leakage through doors, etc.

I forgot to add a third point in my last post - I have seen relatively large (e.g. 12K BTU) A/Cs with digital thermostats…so it can certainly be done, and successfully…