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Forum Index : Microcontroller and PC projects : Airconditioning mod
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lew247 Guru  Joined: 23/12/2015 Location: United KingdomPosts: 1702 |
Does anyone have any knowledge of airconditioners? I have a split unit Fujitsu and the room temperature does not go as low as I'd like it to. The unit is a 1200BTU unit and plenty bog enough for the room it's in. There are 2 thermistors in the wall unit indoors One for measuring the room temperature and one for the indoor heat exchanger I was going to try and make a wifi or bluetooth thermostat to control the aircon unit but there is no return feed from the IR so there is no way to attach it as far as I can see. The one thing I did think of was replacing the thermistor for the room temperature with a proper temperature sensor and simulating the resistance somehow and possible being able to remote mount the temperature sensor nearer to where I sit rather than having it inside the aircon unit itself. Does anyone have any ideas or suggestions? I've found this  and here are the resistance values and voltages for both thermistors at various temperatures  |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7937 |
Although we used to install some small aircon systems we tended to treat them as "black boxes" most of the time. There wasn't usually a lot you could tweak. Normally, if you aren't getting a low enough room temp then the system is undersized for the temperature difference that you are trying to get. Have you considered that the gas pressure might be low and it's running inefficiently? I doubt if you'll get much more out of it than it was designed for. I wouldn't mess with the heat exchanger temp sensor unless you are *certain* that it's not part of a anti-icing and/or over-temp safety system too. The room temp stat is probably fair game for fiddling. :) I'd be tempted, initially, to simply lengthen its wire and try it in a different location temporarily. If that works then move it. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1993 |
How old is the unit, did it ever run ok ? After the unit has been running for 10-15 mins. feel the suction line at the outdoor unit (the larger of the two pipes) it should be cold and wet. If not the unit is likely short of gas. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
I assume it is summer and you are cooling? What temperature do you have the unit set for and what are you achieving. The one annoying thing about my Fujitsu is the lowest I can SET for heating is 16 degrees C. Overnight I would prefer 12 in winter. We turn it off and set a timer instead. I think cooling has a different minimum but you will have to wait a few months before I try it. Jim VK7JH MMedit |
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| palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1993 |
I may have misunderstood the problem. You don't give any values, I have a Fujitsu and the lowest temperature it will set to is 18 deg C. So do you want to set it lower or the unit is set to its lowest and can't reach the set temperature. In other words your unit is working OK and you want the thermostat to set lower. It is obviously an inverter unit so I don't think there is much you can do. The control does not just cut the unit in and out but as it nears the set temperature the compressor speed ramps down until it reaches a speed where it just idles away to keep the room at the set temperature It also has an electronic expansion valve that is controlled by the thermostat. I did work on them but retired not long after the inverter units became popular. I think you need to ask a Fujitsu technician. Edited 2021-06-02 09:30 by palcal "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
I am only guessing that it is the set temperature that Lew wants lower. I did consider putting a small heater under the control unit to fool it into thinking it's hotter in the room than it really is. I'd rather do that than butcher the controller. Jim VK7JH MMedit |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2950 |
Lew, Are you sure it's 1200 BTU? That equates to approx 350w which is extremely small even 10 times that is only really good for a smallish room like a bedroom. I don't think you need as much air conditioning as we do in Aus where it can get to 40c in the summer, even where I live in Melbourne.... the air conditioning we use at home are 8.2kw or roughly 28,000 BTU. This size does the kitchen, dining and lounge (open area) guessing at roughly 8x7m in size.. Regards, MICK Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2640 |
A trick I have used is to fool the system into thinking the temp. is a little higher than the actual temp by adding some resistance in series with the thermistor. Measure the resistance of the thermistor at both the lowest setpoint and at the temp. you want, then add a resistor equal to the difference. You will have to remember the temp. offset when changing the setpoint. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1584 |
-IF- the machine is working correctly and has the capacity, why would anyone want to go cooler than the 16-18 which is the std lowest temp? If you are still feeling too warm at those Temps, you need to see a doctor! :0) |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
Some parts of the world use their heat pump to HEAT, not just cool. When in heating mode, it is too costly to leave the unit running overnight. If I could set the temp to around 12, I could leave it running and catch any really cold nights while being reasonably economic. VK7JH MMedit |
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| palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1993 |
@ Davo99, Don't know your location but it is very interesting how people acclimatise to their environment. I live in the tropics and our air conditioners never get set below 26 deg.C They are mainly used to drop the humidity. When the temperature here drops into the low 20s I can no longer wear the customary singlet and shorts more like track pants and top. Where as Tassie Jim would probably be comfortable in shorts and tee shirt. Edited 2021-06-02 12:38 by palcal "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2640 |
Oops! I got it backwards. You need a parallel resistor to reduce the setpoint. My place is on a mountain, so same as TassyJim. Edited 2021-06-02 12:52 by phil99 |
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| lew247 Guru Joined: 23/12/2015 Location: United KingdomPosts: 1702 |
Sorry English hours, just got up :) It's 12000 btu not 1200, that was a stupid typo, and it's only 2 years old. Its set to it's minimum of 18C but where I sit in the room the temperature is around 21.6C I'd like to move the thermistor externally to the unit so it measures temperature in the actual room and not at the airconditioner unit itself. It's frustrating because I did a lot of research yesterday and other models in the same line have external temperature control displays with temp sensor inside it as an option, but my model doesn't I'm guessing if I opened up the unit the expansion port would possibly be there but it's probably not enabled in the programming so it would be a waste of money buying one. I think the best idea so far is to measure the resistance of the thermistor, and if it is working properly, try and move it outside the wall unit by extending the cable not certain this would work but worth a try. Edited 2021-06-02 16:38 by lew247 |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7937 |
These small aircon units are for single room use. Very neat little things with around 5-6kW heating & cooling capacity. They often have a remote control - like a TV remote. They aren't comparable to what you'd find in hot climates - these are temperate zone beasties really. Because of how they work I'm not sure that you can extend their range very much at all. We sometimes fitted two of them at opposite ends of an office where i wasn't practical to put a "proper" system in for some reason. You can fiddle with the room stat to make it think the room needs cooling. That will increase the run time, but it will probably still cycle on the coil temp sensor as there is a minimum temp that the cooling coil can be run at before you get icing and it becomes ineffective (and messy). These are only small devices so the coil isn't very big. Edit: If there is a sensor on the coil, Lew, don't mess with it. You should be able to extend a sensor that's in the airstream (probably on the incoming side as it's looking for room temp). And 12000 btu is a lot bigger but I'm leaving what I wrote because it's still not huge. :) Edited 2021-06-02 17:11 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1097 |
Re min temperatures. For interest, I checked my Daikin 5kW+ units last night. They go down to 10deg for heating. Ran one over night at 15deg. (Chilly morning forecast). It cycled on & off throughout the night, mostly on. Room warmish this morning. Might try it at 10deg tonight & see what happens. ChopperP |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1584 |
Yes, I am aware of that and have used my ducted system like that for years. I have plenty of solar to offset the cost which reduces it substantially but the main problem is the freezing and below temps we get here where it becomes useless. They only transfer heat, they don't create it. Cannot for the life of me see why that would be worthwhile. The other thing that strikes me is if you are heating to 12 and think that's keeping you warm, the outside temp is likely to be well below the heat pumps efficiency curve and probably doing no better than direct resistance heating. I have been running a small 5Kw China Diesel heater the last few weeks. I pay .28C Kwh for electricity. I worked out for the heat delivered by the diesel heater, it is about half the cost of electricity. If your power cost was more and Diesel around the same, 1.30 L or if one could get heating oil which is non road taxed Diesel or old contaminated Fuel, then it would be even more economical to run the diesel heater. I am also playing with blending with Used veg oil but have not come to any conclusions about the long term viability of that. At 33% and below it seems to run fine. At worst all one would need to do would be pull the heater apart at the end of winter and clean out any build-up which would not be hard to do and there is endless info online how to do it. With a little care and diligence, I do not see offsetting the fuel costs with used veg to be a problem. All depends if people are willing to get their hands dirty and do something for themselves or just want it all at the flick of a switch. I'm happy to put in some small effort for the comfort and savings in return. My home is large and has far too many windows and doors which are crap for keeping it warm or cool. The heater seems to be doing a good job of keeping the greater area of the place ( wouldn't expect the heat to go all the way up the other end of the house through the hall way and round the corners) warm and very comfortable. They are designed for caravans and motorhomes but with a max of 4Kw delivered heat and the ability to run all day and night as mine has done, one is able to keep the place warm by not letting the thermal mass get too low which then radiates cold no matter how much you heat the air till it all comes up to temp. We had 3o here last night and I had the heater on 2 out of 6 heat setting and this morning when I got up it was 19 in that end of the house. bedroom at the other end was 17. The ensuite which is at the far end and closed off was 13 the last few days and is like a frigging ice box. Been solar thermal heating that today and it's been working really well with just one solar panel and not even using the power generated other than to run the fan pushing the heat in. A nice sunny day today and it's sitting at 21 atm up from 13 this morning. I have a thread on that and the diesel heater here for anyone interested. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1584 |
I'm on the outskirts of Sydney where winter can be -5 and Summer 45. we had a week last summer, mild as it was here overall, where the daytime temps exceded 40o every day for 8 days. one night it did not drop below 40 till 9 pm. That makes the average lows of 5 to -5 quite a contrast. I have many times gone up the gold coast in July for work. as with what you say, I think it's hilarious when I'm walking round Surfers in T shirt and shorts sweating when all the locals are rugged up like I would be at home and complaining of the cold and it's about 23 ambient and much warmer in the sun. One year the Nights WERE cold but My wife and I were shaking our heads at how all the young girls we were working with were dressed up wearing nothing walking round at night and going out to the Clubs. Oh to be young again.... or just lack that much feeling. Yep, that's what I'm talking about! I think it wears off though. I was worried this past couple of months that things had been unseasonably warm for the time of year. I was saying that there has been no chance to acclimatise and when the cold hit, it would hit hard. hasn't been too bad so far but then again, the house has been kept warm or at least avoided the cold chill. I still don't see how or what good having the house at 12o would do though. Even the YT vids I watch where the Russians whom live in snow for 6 months and can be -30C outside have their homes heated to 20 or so. |
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| Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1097 |
Nothing happened!!! Off all night. The room didn't get cold enough. I didn't think it would. ChopperP |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1584 |
Maybe you should think yourself lucky. I certainly would! No way I'd want my house getting that cold inside! I got a diesel heater going to try and avoid it! :0) |
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| Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1097 |
Yeah, 10deg is a bit coolish. The AC was set & running at 23deg until midnight. We have a 2 to 10deg day forecast for Toowoomba on Thurs. That will be a fun day especially those attending FarmFest out at Kingsthorpe. Been reading the Diesel Heating posts on the Other forum. Interesting to say the least. ChopperP |
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