Minisplits have a mind of their own?

[1201]

I love my minisplits. I can't go back to regular units.

But, they just arbitrarily decide what temperature they want to be at, and practically ignore the thermostat.

Why?


I like to set the temp to 74 degrees at night, in the summer. At least 8 times out of 10 they will be at a temperature higher than 74. I've tried even setting temp to 68. I still wake up to a temp of about 66 or 67.

Are they undersized??? A resounding no! I watch these things with iotawatt and they ramp down from 1800w to about 500-600w after around 30 mins, even if they are nowhere close to temp. Tf?

today I set them to heat mode. Set temp to 74. 45 minutes later house is 76 and they are still pumping heat.


anyone know what's going on and is there a fix?

 

[1201]

Oh by the way these are ducted and they have a remote wall mounted thermostat

 

[RCinFLA]

One of the issues with mini-splits, window units, and portables is lack of sufficient separation between their return air and output grill air.

Immediate, or short path return of cooled output air cuts unit efficiency and causes thermostat temperature to be satisfied even though the room is not near thermostat settings.

 

[Lt.Dan]

I experience this often with the mini split in my garage. I always have it set to 78, but I'll walk out there and its 74*, and still pumping cold air. No idea.

 

[OPTIMALSOLAR]

How about trying a fan near the exit to blow the hot or cool air. It seems to work with my dual hose unit. If not used the room freezes/over heats or turns off unit too quickly at less extreme settings. Air flow.

 

[Quattrohead]

I think it's due to lack of mixing of the treated and untreated air and placement of the thermostat / remote control. Personally I have not experienced this but I keep the remote control off to the side wall, well out of the air flow.

 

[Partimewages]

Might be easier to help if you post what model you have.
Thermostat also

 

[Will Prowse]

Yeah I think about this a lot, they need a remote thermostat sensor.

In Vegas mine are either on or off. Maximum output. But it's still noticeable to me as well. When I walk into a room and it's freezing, it is frustrating. I have been running my fans to mix the air faster so there are less chance of cold spots developing

 

[1201]

One of the issues with mini-splits, window units, and portables is lack of sufficient separation between their return air and output grill air.

Immediate, or short path return of cooled output air cuts unit efficiency and causes thermostat temperature to be satisfied even though the room is not near thermostat settings.

I would think this but the thermostat shows the temperature of where it's mounted and its accurate, yet it will ramp down before it gets to temp

 

[1201]

I experience this often with the mini split in my garage. I always have it set to 78, but I'll walk out there and its 74*, and still pumping cold air. No idea.

I have a friend whose Mr cool does this. It just keeps pumping cold air and will freeze them out. Mine rarely does this. If it's set to 79 it might get down to 77 but no lower. My problem is the opposite- I set it to 74 at night and it stops at 77.

 

[1201]

I think it's due to lack of mixing of the treated and untreated air and placement of the thermostat / remote control. Personally I have not experienced this but I keep the remote control off to the side wall, well out of the air flow.

My thermostat is nowhere near the airflow. Dolly ducted are strategically placed near outside walls and the thermostat are as far away as possible from them

 

[1201]

Might be easier to help if you post what model you have.
Thermostat also

www.minisplitwarehouse.com/product/midea-18000btu-custom-mini-split-hyper-heat-pump-air-conditioner

Remote

www.minisplitwarehouse.com/product/midea-legacy-wired-thermostat

Yeah I think about this a lot, they need a remote thermostat sensor.

In Vegas mine are either on or off. Maximum output. But it's still noticeable to me as well. When I walk into a room and it's freezing, it is frustrating. I have rubbing my fans to mix the air faster so there are less chance of cold spots developing

I read about that happening but these already have remote sensors. Confounding

 

[timselectric]

I haven't experienced this with mine.
But it does sound like something is wrong.
Either the thermostat isn't reading the room correctly.
Or the programming is out of wack.

 

[Partimewages]

Check your manuals and see if there is a setting to use remote sensor.
It's probably buried in the details somewhere. We have integrated 1000s of minis and even in the same model sometimes they are different. The manuals are not very clear either.

 

[Bob B]

Check your manuals and see if there is a setting to use remote sensor.
It's probably buried in the details somewhere. We have integrated 1000s of minis and even in the same model sometimes they are different. The manuals are not very clear either.

I'd vote for this one .... Sounds like it's not actually using the temperature from the thermostat.

 

[Lt.Dan]

Using the remote for a thermostat doesn't change anything (for me), so I stopped using it.

The mini split even KNOWS what the correct temp is, according to the app:




But even though it knows its 75*, it keeps on chugging. Not very much, but its still unnecessary

 

[400bird]

This entire thread is discouraging, I have been looking to add mini-spits to our house and the ancient central AC shows it's age. With all the talk about variable speed compressors and fans, I thought temperature control would be better than with central AC letting the temp raise and fall 2 degrees.

Are these units that struggle with set points part of a multi head system? Like 2 or 3 indoor units for one outdoor/compressor.

 

[Shimmy]

I'll disagree with the conventional wisdom here; it isn't the temperature sensing that is an issue it is the overall control logic and capabilities.

Assuming refrigerant pressures are per spec: If it over cools it is because it is oversized for the (current) load and the compressor cannot turn down enough. It is trying to manage humidity in the background so it doesn't cycle the compressor when it should. If it doesn't dehumidify enough then it is either undersized or the temperature set point is too high.

I was so frustrated with mine that created a dashboard in Grafall a with data from my weather station and power read from my IoTaWatt to get a better idea of what is happening. I chart indoor and outdoor temperature and dewpoint, along with unit kW and kWh. I was also able to get it to plot a psychometric chart over time to better grasp the comfort aspect.

All that said, I would still rather have the mini split over central AC; it "works better" with central AC because expectations are so low.

 

[1201]

Check your manuals and see if there is a setting to use remote sensor.
It's probably buried in the details somewhere. We have integrated 1000s of minis and even in the same model sometimes they are different. The manuals are not very clear either.

The thermostat has a "copy/follow me" button to use the wall mount thermostat temps.

I always use that setting. It also shows the actual temp at the thermostat

 

[Shimmy]

This entire thread is discouraging, I have been looking to add mini-spits to our house and the ancient central AC shows it's age. With all the talk about variable speed compressors and fans, I thought temperature control would be better than with central AC letting the temp raise and fall 2 degrees.

Are these units that struggle with set points part of a multi head system? Like 2 or 3 indoor units for one outdoor/compressor.

There are a few hacks you can do to improve things, and you should make sure you install them "correctly". Many brands have hidden settings like temperature offset that can improve the correlation between set point and room temperature. Integration with home automation is possible on some, which can do games like adjusting the temperature set point throughout the day/night for various rooms.

But, if you don't run them continuously you have a physics challenge between pull-down time and constant load.

Try to install them at 8' above the floor max, with proper distance to the ceiling, and not in adjacent small rooms that are connected by a single door.

 

[ChrisG]

I'll disagree with the conventional wisdom here; it isn't the temperature sensing that is an issue it is the overall control logic and capabilities.

Assuming refrigerant pressures are per spec: If it over cools it is because it is oversized for the (current) load and the compressor cannot turn down enough. It is trying to manage humidity in the background so it doesn't cycle the compressor when it should. If it doesn't dehumidify enough then it is either undersized or the temperature set point is too high.

I was so frustrated with mine that created a dashboard in Grafall a with data from my weather station and power read from my IoTaWatt to get a better idea of what is happening. I chart indoor and outdoor temperature and dewpoint, along with unit kW and kWh. I was also able to get it to plot a psychometric chart over time to better grasp the comfort aspect.

All that said, I would still rather have the mini split over central AC; it "works better" with central AC because expectations are so low.

Did the exact same thing with temp monitor, Grafana and Emporia. During the days in the graph, outside temp was close to 32°F. Mini-split is kept at 62° for heat when not there. Can correlate power usage with temp. Mine holds temp really close to set point. As it gets colder it will be interesting.

 

[RV10flyer]

I have a 9000 BTU 33 seer Fujitsu mini split. If I set the remote on 70°F, it maintains 70°F all summer and all winter. I have a four probe temperature monitor displaying return air, supply air, 1/2” copper refrigerant line and outdoor temperatures. I think the higher price, better quality makes a difference. Same with EG4 vs Sol-Ark or Schneider.

 

[1201]

This entire thread is discouraging, I have been looking to add mini-spits to our house and the ancient central AC shows it's age. With all the talk about variable speed compressors and fans, I thought temperature control would be better than with central AC letting the temp raise and fall 2 degrees.

Are these units that struggle with set points part of a multi head system? Like 2 or 3 indoor units for one outdoor/compressor.

Mine is not a multi head unit. The minisplit is not perfect but I wouldn't ever go back to conventional.

They are quiet, energy efficient, have no startup surge, and ridiculously affordable.

 

[42OhmsPA]

I'm in agreement with others, it's not reading the thermostat or has some bad logic.

I only have a single head Pioneer Inverter++ series with no remote thermostat... I have no issues with drastic temperature swings. It keeps the room within a few degrees of setpoint.

 

[400bird]

Can everyone share the brand/model?
I wonder if RV10flyer is into something...

I have a 9000 BTU 33 seer Fujitsu mini split. If I set the remote on 70°F, it maintains 70°F all summer and all winter. I have a four probe temperature monitor displaying return, air, supply air, both copper line temperatures.

Are the temp sensors part of the mini-spit? Or your monitoring?

Good to hear about the Fujitsu, that is on my list of possibilities.