Adjustiing/mod'ing digital thermostat on LG window air conditioner

[Dan]

I just bought an LG 8000 BTU window air conditioner, model LWHD8000RY6. The unit has a digital thermostat, which on its lowest setting displays 60 degrees. However, it is not possible even on this lowest setting to get the machine to put out cold air below about 69 degrees. Note I do not mean the machine does not have the capacity to cool the space (a bedroom of about 175 sq') below 69 degrees, but rather, the thermostat shuts the compressor off at 69, even when it is set at "60". I tried moving the electronic temp sensor (thermistor?) from the front of the evaporator to a position out in the room, thinking this spot would be warmer & therefore the unit would run longer. This dropped the room temp about 2 degrees further, to around 67. My wife & I would prefer about 65, if not lower, for sleeping. Again, this is not a case of the unit lacking the cooling capacity to reach lower temps, the thermostat just won't turn the compressor on any lower. So I am wondering if there is generally a way of adjusting these digital thermostats (I had a similar issue with a unit having an old style mechanical thermostat, the type which can be adjusted be varying the spring tension on the thermostat, tweaking this I was able to get the unit to attain a lower temp). Perhaps there's a trimmer pot on this electronic thermostat which can be tweaked? As a second option, maybe I could connect a wall mount thermostat of the type used on a central air unit, which would be more accurate. Does anyone know if this can be done? I'm guessing the thermostat on a window unit directly turns the compressor on and off, and therefore has the current switching capacity required for this, while a wall mount type for a central unit probably signals a central control board on the furnace/ac, which has a relay that does the actual switching. Is this the case? I could probably set up a relay, still we're beginning to get to the point of a lot a screwing around by that time. Anyone have any ideas?

TIA

Dan

[i.hate_spam]

I also have an LG air conditioner with digital controls and would like to do the same. Mine is a rather large and expensive unit, so I am reluctant to butcher it or risk damaging it. I am curious as to what type of component the temperature sensor is.

If the temperature sensor for the digital controls is a thermistor then it would be easy to make a circuit involving a central AC thermostat (you would need a stat that uses a relay output instead of a triac) and a couple of resistors to emulate the sensor indicating a high temperature or a low temperature to manually control the compressor.

If the sensor is some sort of temperature sensitive transistor, it would be a bit tougher to design a similar circuit. If it's a thermocouple, it is even worse.

If you were to do something like this you would have to beware of evaporator coil freeze up, especially at the temperature you wish to run the unit at, since the temperature sensor is no longer in front of the coil. Evaporator coil freezup can easily ruin the compressor.

Eric

[Dan]

Eric-Thanks for the reply. I agree about the freeze up potential, have to keep an eye on it at least initially. I have forced it to run longer by holding the temp sensor between my fingers for a period of time, so far minimal frosting on the evaporator. On the other hand, it's not that humid here at the moment. Another option might be to slightly heat the sensor with something like a low wattage light bulb placed at a distance, though again this is kind of a PITA, especially in a bedroom :-/ This particular unit was fairly cheap, about $160.

Dan

[Mike Berger]

[Ken Weitzel]

Hi Dan...

I suspect you and your wife might like a 5 or 10 watt ceramic resistor with a half amp or so at 12 volts better than a light bulb :)

However, I respectfully suggest that perhaps you and Eric are asking more of a home cooling unit than it was designed for and intended to do. Think perhaps you guys liking to sleep at

65 degrees F are in a real minority. Not to mention the cost on your hydro bill :)

My car has auto climate control. Switched to "US" mode, the auto temp will drop degree by degree, until it suddenly jumps to 50F. I'd assumed that meant that it would run virtually forever, or until it reached 50 if ever. Not so, just tried it. Something else shuts it down long before it gets that cold.

Just my 2 cents, FWIW

Take care.

Ken

[Dan]

Yes, it's the thermostat. After I pulled the sensor from the front of the evaporator, holding it in my hand momentarily warms it enough to get the compressor to kick in.

Dan

[Dan]

A power resistor is a great idea! Why didn't I think of that!?!

Hydro bill shmydro bill ;-) I don't doubt you're correct about our preference for low temps. We open the bedroom windows in February! Honestly though, I have met others who also like sleeping in the cold. I have been able to attain the desired temps with other 8kbtu window units in another bedroom in a climate with a much higher heat load applied; hotter weather, higher humidity, less insulation, less shade, etc. I think the unit is capable of what I want, the thermostat just doesn't think so ;-)

Probably the same thing, the thermostat is killing the car's AC compressor clutch before it gets to the indicated temp. I didn't really expect the "degrees" indicated by the unit's digital readout to be all that accurate, but if they have a scale going down to 60, I really do think the damn thing ought to be capable of more than 69 when used in a space of the size etc. indicated by the btu output.

[J. Clarke]

If I may venture a stupid question, are you sure that the thing isn't simply defective?

[Rheilly Phoull]

I'd be thinking of a pot in parallel or series with the thermistor. Assuming you dont want to open up the controller to find adjustments.

[Andy Cuffe]

I suspect they are limiting it to 69 in order to save energy (probably an EPA regulation). The simplest solution would be to buy an A/C with an analog thermostat. It's probably possible to modify the digital thermostat, but you'd have to figure out how by tracking the circuit and looking for data sheets for any ICs. It's probably custom to that A/C and it will be impossible to find a schematic. It might be as simple as a jumper to switch it to non-EPA mode, or you might have to modify the temperature sensor circuit. If you modify the temperature sensor, you'd have to live with an inaccurate temp display (eg. it still shuts off when it thinks it's 69, but it's actually 65). Andy Cuffe

[e-mail]

[Dan]

I thought of that as well, easy enough to check but at the moment I'm not sure it IS a thermistor...

Dan

[GregS]

Round bulb in center of evaporator? I'm just listening. I am going to try and set mine to below the mark tonight. Mine just has a 9.7 rating.??

greg

[larry]

my 5K gold star window air: bg5200er limited schem on top of black plastic control box) sensor - thermistor(non polar) in black epoxy glob: oF ohms

212 = 1.2k finger(98) = 6.6k warm room(82) = 7.8k 32 = 26k

negative factor (hotter = lower resistance)

draw a linear chart, see if my numbers are on the line

use ohms law

have fun

-larry / dallas

BTW- if anyone trashes one of these, I would like to buy your circuit board and keyboard/display. I have a GE I want to teach new tricks ;-)

[Dan]

Thanks Larry, very interesting info. If the sensor in mine also turns out to be a thermistor (a likelihood) it really simplifies tweaking. In the case of your figures, you could fool the thermostat into thinking it was 98 when it was actually 82 by shunting the thermistor with 42,900 ohms. Since the range of actual thermistor values over real room temperatures would be fairly narrow, something along these lines would probably be safe (only down side is the temp readout would be wrong, but since it is anyway (says 60 when it's 69) no loss there). Also very easy/cheap to implement.

Dan

[Ken Weitzel]

Hi Dan...

With all this great info, seems you can't go wrong! :)

Another suggestion might be to consider using perhaps a 100k variable rather than a fixed resistor.

A bit of tweaking might let you make the readout "wrong" by

10 degrees F, so that for instance you could more understandably have 65 degrees read 75, etc.

Take care.

Ken

[Dan]

I agree a pot is the way to go, after calculating a ballpark figure.

Thanks!

Dan

[zekor]

I didn't note the model # but I just bought an 8000 BTU at The Home Depot. I tested it and it goes to 60 deg. I put a thermometer near the sensor.

gs

[Dan]

Thanks for the reply. I checked the temperature across the room on a bedside table. Since the sensor is on the evaporator, it may very well get to 60 right there, unfortunately it's a little cramped for living space under the filter ;-) With mine set at 60, the lowest I could get it in the room was 69, this on a day that wasn't more than about 74. I attached a 100k pot in series with a 47k resistor across the thermistor, adjusted to about 75k total (have to remove & measure to be sure) I was able to get the room down to 61, with an outside temp of around 75. I don't plan to keep the room this cool, but it does show the machine has the capacity to lower the temp sufficiently if the thermostat tells it to. Very easy mod, in case anyone else has a similar issue with a room AC.

Thanks again all who replied.

Dan

[Connie]

replying to Dan, Connie wrote: How do u do this. Mine does the exact same thing and it used to go lower than

69.

[Dave M]

The internal temperature sensor (a thermistor) might be defective. If you aren't electrically or electronically savvy, I'd suggest that you call an A/C service company or remove the unit from the window and take it to a service shop. If you can handle an electronic repair, You should download the service manual from

The service manual contains the full schematic of the unit, complete with parts list of replacement parts.

Dave M