Deloghi Bran 41 heat pump lp fault

Hiya.
Had a call to a heat pump this week.
Lp alarm.
Heat pump runs for approx 1minute before it trips on lp alarm.
Pressure in system is fine 8 bar approx at 2oc.
Sight glass shows system dry.
Start it up high side goes up straight away 20bar + low side falls rapidly to 1 bar and trips out.
I cant really get it to run long enough to check temperatures across the filter dryer but i think it is reading a difference.
Seems like a near total blockage at the dryer.
Took off the txv bulb and made no difference, also opened up the txv but that made no difference.
When i turn it off the 4 way valve de energises and the system pressure equalises.

So looking at blocked filter dryer i think.
Delonghi heat pump approx 4 years old.
No problems till now, we regularly service it and no repairs done to refrigeration side.
Any help appreciated.

You say that the pressure is fine with 8bar at 20°c or is that 2°C? If this is the standing pressure of your refrigerant how do you know that it is fine?

You haven't stated the refrigerant type but when you run it the pressures obviously aren't correct, or fine.

Have you checked for leaks yet, are the fans operating correctly, are the coils clean?

Hi Brian
Yes its 8bar at 2 degrees c and standing pressure.
Think its fine with the way it is running, if it was short on gas it would not be doing this.
Its 410a.
Had a visual check for leaks and have seen nothing, fans are fine and coils clean.
Thanks
Sean

To change the drier you'll need to recover anyway so kill 2 birds etc

yes.
I couldnt do that on Friday as it was a day of snow and f7.
but would like a confirmation before i do that if anyone knows.
Thanks

Hi heatsave.
I am intrigued and must admit, that I don't work on Heat pumps often enough.
To profess to know enough about them.

I note you are in the Shetlands, so you would work on these in all conditions.
If this system is a ground source?

The ambient won't have such a big effect I assume as if it's air to water?
You don't say which, does the Model title / type reference which it is?
Is there a minimum ambient at which these systems stall or become ineffective?

Sorry for being thick! But what's f2?
Grizzly

Hi heatsave.

Reply re-directed.
Sorry wrong recipient!
Grizzly

Hi there.
yes its usually a survival suit working on them at this time of year!
Its an air source heat pump.
Its a Delonghi Bran AW0041.
fitted about 30 of them and the refrigeration side is usually bullet proof but not on this one.
They will max out at -5 so ambient is not a problem.
Think its a blockage somewhere as it goes into low pressure so fast and pressure rises so fast on the high side.

its not f2 its (F7) force 7 wind !!

We have electrical back up in the buffer cylinder on the heating side and of course in the HW tank so the customers are managing but at these low telperatures a 3kw immersion is just managing to keep the property warm.
They have 2 children one just out of hospital so eager to see if anyone have any pointers.
I have emailed Delonghi about it.

Quote:

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Originally Posted by Grizzly

Hi heatsave.
I am intrigued and must admit, that I don't work on Heat pumps often enough.
To profess to know enough about them.

I note you are in the Shetlands, so you would work on these in all conditions.
If this system is a ground source?

The ambient won't have such a big effect I assume as if it's air to water?
You don't say which, does the Model title / type reference which it is?
Is there a minimum ambient at which these systems stall or become ineffective?

Sorry for being thick! But what's f2?
Grizzly

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Think a faulty TEV more likely.
Can you rig it so the RV doesn't let the system equalise on shut down? I'm thinking run it till the suction get down low, shut the compressor off then look for frost forming at the restriction.
Maybe link out the LP, run it and bleed some gas across your gauges to keep the suction from getting too low, a minute or two may then show a temp drop across the drier if this it the problem.

Yes I can try that, just need some better weather!! thanks for getting back.

Quote:

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Originally Posted by monkey spanners

Think a faulty TEV more likely.
Can you rig it so the RV doesn't let the system equalise on shut down? I'm thinking run it till the suction get down low, shut the compressor off then look for frost forming at the restriction.
Maybe link out the LP, run it and bleed some gas across your gauges to keep the suction from getting too low, a minute or two may then show a temp drop across the drier if this it the problem.

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Hi Sean,

On top of what MS says, can you equalise then run the system then watch the sightglass. Hopefully you can see something in there to begin with, if it fills up then it looks like the TEV is faulty, if it empties out then the filter blocked.

I know sometimes it's hard to tell if the glass is full or empty.

Cheers,
Andy.

Hello Heatsave ,
how does sysyem run in cooling mode? I have had a bi flow drier break one of its check valves and would run fine in one direction and be a total block in other direction. This sounds like a similar situation that you have.
Hope this helps.