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SmokeyJ

Gas Engineer
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Hi all
After checking jobs for the week I see the office have booked me in to a customer who has a Danfoss DHP-AX heat pump. She has had ongoing problems with the unit cutting out and displaying 'low pressure' error. Another company has tried to fix (only info is - replaced filters, altered pipework etc) and no further to resolving fault. She did mention to her knowledge they have not checked the external unit...
My experience with heat pumps is limited and I don't do the refrigeration side. We have an air con engineer on firm who can check the refrige side. I am just wondering if anyone has come across this problem before? Am I right in thinking it would be better suited for the air con engineer to attend and check refrige pressures, low pressure switch etc. Or is there an external factor that can influence this issue that I can check i.e flow problems?
I don't like going out to heat pumps with not doing refrigeration as it seems you can only do half a job.
Thanks Jason
 
Low pressure trips can be a number of faults, has it been like this ever since it was installed? If so, is it correctly positioned?

If the fault is intermittent, it is not likely to be a loss of refrigerant gas as it would be constantly tripping out. Any other fault symptoms accompanying the low pressure trips?
 
Have not been to site yet so unsure of any other symptoms or history.
Only info i have is from an email 'I have a danfoss DHP-AX, The system cuts out when low pressure error shows on the display panel. I spent just ÂŁ1000 with a company who seemed to replace filters and added a bit of extra piping etc... They never checked the unit outside and never fixed the problem'
Apologies if i'm sounding daft , so it could be various things that could cause fault. Only external factors i can think would be airflow or circulation based issues or am i missing something? All other factors would be related to the refrige side? Just makes sense to me to get the refrige checked at the same time so i may save chasing my tail if it is say a faulty low pressure switch. Or am i taking the wrong approach
 
What is the low pressure error referring to?

Refrigerant side or water side.

It's probably something you should find out from the customer prior to attending the property.
 
I am assuming it's the low pressure on the compressor side. Don't see a mention of a low pressure switch on the water side in the manual. In the trouble shooting guide there is loads of things to check. It mentions various checks on the 'brine' circuit. Have not heard of a 'brine' circuit before, is this just another wording for the heating system
 
We look after an estate in Leeds with about 30 AX air source heat pumps. They are not the most efficient unit but they are pretty reliable refrigeration wise. Its worth checking the connectors within the internal control panel as I have a good few with both high and low pressure errors being down to a bad connection on the plugs on the PCB a squeeze with a pair of pliers does the trick.
 
I am assuming it's the low pressure on the compressor side. Don't see a mention of a low pressure switch on the water side in the manual. In the trouble shooting guide there is loads of things to check. It mentions various checks on the 'brine' circuit. Have not heard of a 'brine' circuit before, is this just another wording for the heating system

Brine would imply it's a GS heat pump. 1+1=2. Job done.
 
Quality - Thanks I'll give them a check.
Howsie - I was wondering but I'm sure its a ashp, thinking troubleshooting guide in manual may be a bit generic. Manual I have is for the dhp-ax ashp.

Main query was if it is likely to be a refrigerant or a water side issue. Seems that it could be either so I'll go have a look
Work mate said it may cut out on low pressure when on defrost if it's not getting the temp rise from the heating?
Going to site tomorrow so will get more of an understanding of what's going on.
 
Some of the old Danfoss ASHP's were GSHP's with a brine (glycol filled) coil used as an air collector !!! Those are the Danfoss DHP-A and DHP-AX units

The DHP-AQ units are the usual Monoblocs
 
No the DHP AX were their first true DX coil/Evaporator ASHP as opposed to the DHP A which was effectively a ground source unit with a glycol fan coil. The DHP AX are also mono block units
 
Thanks quality, happy to stand corrected, the manuals I have for the AX units have glycol circuits in them .... left hand not knowing what the right hand was doing ?
 
Ps we have an A here sitting in our museum of oddities :)
 
Not a bad unit mechanically its just the control is pretty limited
 
Had a quick look today before she went to work. System working and up to temp.
System is 5 years old and had no problems until a year and a half ago. It will typically cut out on low pressure about 3 times a month.
Previous works seems to be magna clean and auto bypass and possible flush/cleaner (info pretty vague). She mentioned they said it was one of the dirtiest he's seen.
Checked heat pump. Only About 800mm in front of unit to next door, rear ok. Mi's ask for 1500mm so not ideal.
Coil pretty clean, fan ok, pcb connectors seemed ok.
System seems to be circulating fine (flow shown through ufh manifolds). Up to pressure and no air. Cleaned magna clean, not much but quite large deposits rather than the average black sludge. Ran a manual defrost cycle and no issues was about 5°c outside at which point customer had to go to work.
Said she'll call when it next occurs.
Still unsure as to what could be causing low pressure as it is only intermittent. The front clearance/ unit
positioning is not good, but it was trouble free for 3 years. Tempted to give this one a miss as really not in the know with heat pump fault finding. My experience with heat pumps is fitting a couple of ecodans to a spec and that was a couple of years ago. Will pop a couple of pics up.
 
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Is the discolouration on some of the coil piping normal?
 
Are you guys sure that unit doesn't have glycol in it??? That looks just like the A series collector, as opposed to an evaporator...
 
That is 100% a DHP AX the last 2 pictures are of the evapoartor. The ally way its installed in will not help as in cooler weather it will be like walking into a refrigerator which will not help with low pressure issues, But sound as its quite a recent issue I would suggest on the expansion valve being on its way as they do tend to hunt quite a bit because it only a standard mechanical TEV and 5 years service is pretty average life for one. I have replaced quite a few but there were only around 1200 DHP AXunits fitted in the UK
 
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Thanks quality will look into that. I'm a bit reluctant to look into any flow related issue as seems thats the route the previous company took with no avail.
Will have to get our refrigerant guy to test the system. With the TEV is that something you can test or would it be better/cost effective to just change?
Also a little confused now as to wether this system needs glycol? Manual just says fill off the mains, just a normal filling loop on system so don't think so.
Thanks
 
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