@mk4, @tasos — None of it really makes any sense! Despite, not because of, my FOR SERVICEMAN settings as above, I am definitely running in weather compensation mode. If my heat pump is set up with a fixed LWT, then, ahem, my LWT should be fixed. But it isn't, the LWT goes up and down with the OAT. Here's my data from 28th Jan 2026, chosen because there is some variation in OAT:

As you can see, as the OAT goes down, the set and actual LWT go up, and as the OAT goes up, the set and actual LWT go down. It is definitely not a fixed LWT. The LWT values also match my current WCC 52 @ -2 / 31 @ 15, 1.24 degree change in LWT for one degree change in OAT, such that at say 2 degrees OAT we would expect the set LWT to be 52 - (1.24 * 4) = 47 degrees, which is what we see (right hand end of chart), likewise 7 degrees OAT, set LWT = 52 - (1.24 * 9) = 41 degrees (around 1700-1800). The chart also happens to include steady state running at around 5-7 degrees OAT (left hand end of chart and 1600-1800), defrosts below this OAT, when the actual LWT peaks at the set LWT, and 'normal' cycling in OATs above around 7 degrees, when the actual LWT cycles above and below the set LWT. All of the behaviours are normal for my heat pump, and as I say, this is absolutely not a fixed LWT chart!

The way I set up my heat pump is the standard Freedom/Hendra method of setting the WCC endpoints (items 3.8 to 3.11 in the FOR SERVICEMAN menu), and then set the heat pump to use 'curve 9' via the PRESET TEMPERATURE > WEATHER TEMP SET Menu, as described in the Freedom Installation Manual, which was written by GH. This is what I have always done, there is no mention in the manual of going into the TEMP TYPE SETTING menu, and I have never even looked at it until it came up in the current discussion.

All of which is to say we still have the paradox: according to one set of settings pages my heat pump is set up to run with a fixed LWT, on another set of pages it is set up to use weather compensation, and in practice it follows the latter.

@mk4, to address the specific points you mention:

Friend, I think your set up is a fixed LWT. This is what I understand by reading the 2nd manual page you posted.

Friend, I am defo set up to use and am using weather compensation (see above).

According to the same page, in order for you to use wc, you have to enable Room Temp (and disable Water Flow Temp).

Not so, see above and recent posts passim.

And if the (admittedly obscure) manual excerpt posted by @tasos applies to you, once you enable Room Temp, you will:

- be able to choose a wc curve

I can already chose (and routinely do so) a WC curve, but use a different method, as above, which does not need Room Temp enabled.

- be able to apply an offset to the curve i.e. raise (or lower) the curve by x degrees, that is you keep the slope and you just shift it in its entirety up or down the LWT temp axis

This goes back to where we started: as far as i can see, once the WCC is set, either manually (items 3.8 to 3.11) or in my case by my auto-adapt script, then that's it, it's set, until changed by one of these two methods. There is no simple menu option I can see to move (offset) it up or down a degree at a time.

If it does exist, it is quite a find, because it means Midea heat pumps have a simple intuitive quasi 'turn the thermostat up or down' control, similar in concept to Vaillant's simple adjustment control (which does the same thing as I understand it, shifts the WCC). 

- experience what I have been experiencing i.e if the wc happens to raise your IAT up to the room temperature upper limit you defined (or may be plus one degree of that), your ASHP will switch off. Assuming of course you have your wired controller in a living room or so.

I don't have the wired controller in a living area, it's in the airing cupboard. But more to the point, I have never intentionally set a room temperature upper limit, and I am still not clear where I would set it, or more usefully check what the current value is (presumably very high, because the heat pump never turns itself off because the IAT or in my case ACAT, airing cupboard air temp), unless, as I briefly suggested earlier, this does happen, and explains my and most other Midea heat pumps cycle in normal operation. But I am not at all sure about that, it seems to cycle wherever the IAT is,    

The there is another oddity. As it happens my minute data includes modbus register 114, the 'Ta, room temperature', which I presume is the IAT as measured by the wired controller, and so in my case it is the ACAT. It does this because when I wrote the script I included any register that might be of interest. The 'interesting' thing about this value is that it is always 25. Yet on the wired controller OPERATION PARAMETER page 3, the same value ('Ta ROOM TEMP') is blank ('--'), which rather suggests the wired controller doesn't know what the room temp is. Perhaps it is because Room Temp under TEMP TYPE SETTING is off (sort of might make sense). 

And lastly, the place where I might/should be able to set the (desired) room temp, left hand side of the main/home page of the wired controller, won't let me do it, I get the 'Weather temp set function is on. Do you want to turn off it?' message, which I, and I think GH and/or my installer, always took to mean weather compensation ie 'curve 9' was in effect (and so by implication you could not set a desired room temp, hence the 'either/or' thinking). Prior to the recent discovery of the TEMP TYPE SETTING menu, we had no awareness of its existence, never looked at it and didn't need to, insofar as we had a heat pump that was clearly operating in weather compensation mode, and (after big bang) consistently delivering a steady desired IAT. It now seems that the message may refer to the TEMP TYPE SETTING > WATER FLOW TEMP setting rather than weather compensation (my oh my how they love to scramble the language!). I could turn on ROOM TEMP in the TEMP TYPE SETTING page, but I am not sure I need to, given I already have a system that delivers what it is supposed to deliver. If it ain't broke, don't fix it...

But then again, it might be worth trying it, to better understand my system.                 

@cathoderay Are you using Midea's wired controller to operate the heat pump or some other method (modbus or whatever).

Furthermore, even with a fixed set LWT, at say 40C, the actual LWT will fluctuate with fluctuating OAT. 

Posted by: @tasos

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Are you using Midea's wired controller to operate the heat pump or some other method (modbus or whatever).

Please do try to concentrate! I clearly use the wired controller, plus the modbus interface to it, the latter mostly for monitoring, but also to implement my auto-adapt script (which 'adapts' the WCC according to deviations in the IAT, which as it happens are rare, but they do happen). But the final common pathway is always the wired controller, whether I interface with it via modbus or manually using the buttons on the controller.

Posted by: @tasos

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Furthermore, even with a fixed set LWT, at say 40C, the actual LWT will fluctuate with fluctuating OAT. 

??? Is this something out of Kafka?

@cathoderay 

The only explanation that crosses my mind is that your autoadapt script bypasses the wired controller. And this may  explain one of your remarks that seemed odd to me: that everytime you exit Serviceman menu (presumably using the wired controller) you need to reactivate wc (because by using the wired controller you overwrite your automation scripts). Not sure this is the case, it’s an idea…

I liked the ACAT terminology, I think it should become industry standard.. :-).

And it might be interesting to investigate if most midea AHSP’s experiencing short cycling suffer from the ACAT syndrom. If only it were easier to know if a midea ASHP shortcycles, ours may be shortcycling as well  but we have no clue (nor am I willing to spend vigilant nights next to it…).

 @tasos 

Indeed in a fixed LWT actual LWT will vary, but the variation in cathodRay’s case is too large and more consistent with a wc mode. 

I agree that if it ain’t broke, don’t fix it (particularly when it comes to AHSP setup)….

@cathoderay 

If you feel like experimenting, please set Room Temp to YES and Water Temp to NO in your wired controller, just to see if you will be presented with a screen like the one I am attaching. I am really curious to see if midea operation has changed so much from your generation to ours. When did you have it installed?

Posted by: @mk4

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The only explanation that crosses my mind is that your autoadapt script bypasses the wired controller. And this may  explain one of your remarks that seemed odd to me: that everytime you exit Serviceman menu (presumably using the wired controller) you need to reactivate wc (because by using the wired controller you overwrite your automation scripts). Not sure this is the case, it’s an idea…

I liked the ACAT terminology, I think it should become industry standard.. :-).

And it might be interesting to investigate if most midea AHSP’s experiencing short cycling suffer from the ACAT syndrom. If only it were easier to know if a midea ASHP shortcycles, ours may be shortcycling as well  but we have no clue (nor am I willing to spend vigilant nights next to it…).

The auto adapt script goes through the wired controller (because that's where the modbus connection wires are attached) to wherever the actual control circuits are (maybe in the wired controller, maybe on the main PCB in the unit itself, I don't know). It is probably more accurate to say the script bypasses the manual buttons on the wired controller. I could do exactly the same thing as the auto-adapt script does manually, using the buttons, but instead the script does it automatically.

The turning off of the space heating and/or DHW heating (it is not always entirely consistent) after entering and exiting the FOR SERVICEMAN menu appears to be standard Midea behaviour most of the time (as I say it can be inconsistent). Others have encountered it, and it is even mentioned in the Freedom installation manual. It appears to happen by default/by design. That said, because my auto-adapt script bypasses the manual controls, ie it doesn't specifically enter and exit the FOR SERVICEMAN menu, it doesn't appear to turn anything off. But, having said that, there are some lines in the script that check the heat pump isn't in DHW heating mode before making any changes, and I think — it is a long long time ago — I put them there because if they auto-adpat script changed the WCC settings when the heat pump was in DHW mode, then it did turn the DHW heating off.

Most Midea heat pump owners, at least the ones that post data on the subject, appear to experience cycling, but not short cycling. The cycling you can see in the middle of the chart I posted earlier, between 1200 and 1800, is typical, very roughly once an hour give or take. The definition of short cycling varies, but generally it means several times an hour, which may be detrimental, whereas the longer cycling seen in Midea units appears not to carry any obvious penalty.

I don't think my current setup uses the ACAT at all. At the time my heat pump was installed, I was led to believe the heat pump either in WCC mode, based soley on the OAT, or in room temp control mode (with a fixed LWT), based solely on the temp sensor in the wired controller (or I believe an external sensor, there is an option to add one I think). Indeed, because the wired controller samples the ACAT, because that is where it is, I don't want it to have any influence. The other reason for thinking it isn't used is the fixed 25 degree value in the modbus room temperature register, and the fact the wired controller OPERATION PARAMETER page shows the ROOM TEMP value to be '--' ie 'not a number'. For whatever reason (perhaps because ROOM TEMP is off in the TEMP TYPE SETTING menu), the controller doesn't know what the room temp is, or if it does, it doesn't use, record or display it.

Posted by: @mk4

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I agree that if it ain’t broke, don’t fix it (particularly when it comes to AHSP setup)….

Indeed! Especially if you want to avoid HPDHD (Heat Pump Deficit Hyperactivity Disorder)!  

Posted by: @mk4

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a screen like the one I am attaching

I don't think I have anything like that screen. Can you describe how you get that screen? Menu > Next selection > next selection > etc > that screen? I can then try to replicate that as things are now, and then change the TEMP TYPE SETTINGS, and see whether it then does, or doesn't, appear. 

@cathoderay I am pretty sure your unit is set to operate on "Water temperature control" and not on WCC control.

Posted by: @tasos

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I am pretty sure your unit is set to operate on "Water temperature control" and not on WCC control.

Can you please explain why? I do agree it is on that setting in the TEMP TYPE SETTING page, but it is also on 'curve 9' ie the custom weather compensation curve, and it seems to me, looking at the set and actual LWT on the chart I posted earlier, that it behaves exactly as expected if it is on weather compensation. Put another way, it seems that setting it to 'curve 9' over-rides any TEMP TYPE SETTING.

Again, why do you think it is not on WCC control? 

@cathoderay well exactly because it says so on the screen. Furthermore, the fact that curve 9 is shown as selected does not mean it is in effect. I agree though that the graphs deserve further exploration.

Of course all these are my understanding miles away from your installation.

Posted by: @tasos

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well exactly because it says so on the screen

My interpretation of the screens is that one screen shows one setting is on, another screen shows another setting is on, and the problem is they can't both be on, ie one contradicts the other. The best way to resolve this contradiction is to look at what the heat pump actually does, and I think it is fair to say, from the chart I posted earlier, that it does show weather compensation behaviour, and what's more, it has the right 'dose response' curve, ie if I calculate the expected LWT for a given OAT using my current WCC, then that is the LWT that appears at various OATs. Put another way, it is behaving exactly as if it is under the control of my current WCC. I think that means the onus has to be on you to show that it isn't using the WCC.

I do appreciate you are not on site, but I can and do post the data here, which is probably 99.9% of what is need to analyse this conundrum, and I am of course very happy to post any other data you want to see, as long as I have it.

Posted by: @mk4

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When did you have it installed?

Exactly four years ago, February 2022. Here are the instructions my installer used to set it up then, and which I have used ever since, to set up weather compensation, taken from the Freedom Installation Manual. This is the entire weather compensation setup section, there is no mention of going anywhere near the TEMP TYPE SETTINGS page.

In another section, there is this, which confirms the going in through and then exiting via the back door turns off the DHW heating behaviour: