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Mitsubishi Ecodan 11kw Defrosting Issue.

 
Air Source Heat Pumps (ASHPs)
Last Post by ThunderMink 2 months ago
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 ThunderMink
(@thundermink)
Active Member Member
70 kWhs
Joined: 4 months ago
Posts: 4
Topic starter 28/11/2024 8:12 am  

Hello, i am new here and also a newbie on air to water heat pumps.

I recently bought a Ecodan / Zubadan split system manufactured 2019 and installed 2021, it was too cheap (500€) so i could not help my-self from buying it and try to get it working. Outside unit is Zubadan PUHZ-SHW112YAA with the pre plumbed inside unit EHST20C-YM9CR2.UK. 

I installed it in June and found lots of small problems, outside unit dip switches configured wrong and also some settings in the FTC5 controller that made it run really inefficiently, when i first got it running the COP was about 2.0 or worse even tho it was summer and warm weather. Then made some changes to the settings and got the COP up to about 3.2 and that was not too bad, now when the weather has become colder the real problem started to show.

When the outside temperature gets below 0 degrees C the defrosting seems to have some weird issue. I saw that the unit had frost on it so i waited until a defrost cycle started and it worked fine, but then when it got even colder to about -4 to -6 degrees it defrosted many times every day and i noticed that the defrost cycle is much to short so it just starts to melt the ice then stops and resume with the heating causing the unit to freeze completely in a day or two.

 

My first guess to the problem would be the 4-way valve but i really cant see how that could be the issue when it clearly do go in to defrost mode but mostly seem to "finish" the cycle in well under 10 minutes which seem to be a very short defrost cycle.

So now with the colder weather the outside unit is frozen and the COP goes down under 2 and won't completely defrost until the ambient temperatures are just below 0

 

Here are some Melcloud and SD card graphs.

internal temperature
Enery usage
21.11 temperature history

 

operation mode
Defrost zoom
SDcarrd

Could this be a sensor problem or something else? Grateful for any advice on this issue.

 

And greetings from Finland.

 

 


   
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Ecodan Zubadan Defrost
 Westkent
(@westkent)
Estimable Member Member
562 kWhs
Joined: 2 years ago
Posts: 48
28/11/2024 10:06 am  

I had a problem with my ecodan unit freezing up having to literally put a hot air gun on Christmas Eve at 10pm 2 years ago.

Took various engineers over a month to sort out.

Low and behold after all the headaches it mounted to a dodgy temperature sensor mounted at the outside or the outside unit at the rear.

Basically it was sending the wrong signal.

good luck 


   
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 ThunderMink
(@thundermink)
Active Member Member
70 kWhs
Joined: 4 months ago
Posts: 4
Topic starter 28/11/2024 10:14 am  

@westkent Thank you for the info, this was exactly what i was thinking about. i have a Beamex temperature calibrator and a dry well temperature generator at hand so i will check the service manual what kind of thermistors they use and then check the temperature curve and compare with the manual. Best to check them all as they seem prone to failure / drifting.


   
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 ThunderMink
(@thundermink)
Active Member Member
70 kWhs
Joined: 4 months ago
Posts: 4
Topic starter 29/11/2024 4:26 am  

I did not have the time to check the thermistors Yesterday but i am now almost certain that's the problem. I enabled the cooling function on the heat pump and manually "defrosted" the unit by cooling the home. Worked great, had it on about 12 minutes and all the ice was gone. 

At least the 4 way valve should be ok, worst case there is low refrigerant but would not bet on that as the pump both heat and cool very good.

Also i noticed that when using weather compensation i got really bad COP, then when using room auto adapt i got much better COP which also points to the outside unit thermistors. 

This weekend i will test ALL thermistors and hopefully find a faulty one.


   
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Mars
 Mars
(@editor)
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11/12/2024 9:06 pm  

@thundermink can you give us an update on your tests?

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 ThunderMink
(@thundermink)
Active Member Member
70 kWhs
Joined: 4 months ago
Posts: 4
Topic starter 31/12/2024 6:28 am  

@editor Sorry for the slow reply, it looks like a happy new year to me. 4 days ago it was a bit warmer so i got to start trouble shooting a bit more, i noticed that if i completely shut down the system the LEV electronic expansion valves open fully, then the unit defrosted ok for a while so and i started thinking if it is the valves that skip some steps causing the defrosting issue over time when the valves misses steps and is in the wrong position.

I removed the valve heads and noticed one was not fully in place and another one was stuck to the valve body so i sprayed some wd40 to loosen it and then cleaned the stepper motor coils, also the cables was zip tied to the copper tubing and the cable shrink seemed to have shrinked and caused very much tension on the valves wich also can have been why one of the valves was rotated out of place, 4 days now and no problem, it has not been too cold yet but it is now -4 degrees C and i have not seen any frosting what so ever on the outside unit. Also the COP is much better so it seems that this has worked. Still need to wait and see how it behave the coming days as colder weather is on its way (friday forcast -11)

Hopefully the system will work 100% for the rest of this winter 🙂 


   
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