odd behaviour... orifice sizing?

[knighty]

we've been using a 27ft freezer container from the back of a truck as a temporary freezer while we're waiting on a new mains supply for our new big freezer... it was going great until the compressor seized on it

had a couple of spare systems from other freezers which have been removed, fitted those to keep up going, it's a bit of a bodge but pretty much everywhere is closed due to covid-19.

box is empty, door is kept shut, so hardly any heat load on it

I noticed one system had no water from defrost, had a closer look and it's not icing up at all... other system has defrost water and has some ice build up

so left the system with no ice running and turned the other off

setup a tub to catch defrost water... there's non so far, not a drop

box was at -18'C last night and -16'C this morning
(thermostat set to -25'C, working correctly, compressor running)

had a closer look, one of the evap fans has burnt out a winding, keeps tripping out, removed the fan, will have to run with 1 fan until we can get a spare (everywhere close right now)

I'm wondering if orifice is the wrong size? it's a No.4

condensing unit (running 404A)
15523
http://www.siscon.nl/cms_img/danfoss_optyma_plus_with_croll_or_reciprocating_compressors.pdf
15524

I'm struggling to find any info for the evaporator
Friga-Bohn SK009.E Mono
15522

could SKB 09 E be the new model? - dimensions seem to match?
https://www.elektronika-sa.com.pl/tcmodel.php?line=XFCUB-SKB-2005&model=SKB%2009%20E&RID=3&Tab=1
(but has 2x 540watt fans vs my 2x 480watt)


I'll take pressure/temperature readings later on and report back... with only 1 fan running I'd expect excessive frosting

suction line is frosting up back to compressor, condenser fan is blowing warm, but it's a modulating fan speed controlled by liquid line pressure, fan isn't running very fast

I appreciate we're oversized for the size of the box, we use it to freeze fresh meat, so need as much cooling power as possible (it's temporary until new freezer finished)

[seanf]

If its not being used your not putting moist air in the box, maybe the other unit has an air leak.

[knighty]

I had the door open for a good half hour to put a bit of load on it while I investigated

it's not pulling the temperature down now... 12 hours later and box is only -10'C (was -18 before door open)

[RANGER1]

knighty,
I would assume TX valve is sized correctly, first have to provide system information.

pressures, temperature, superheat, air on/off , refrigerant charge.

[knighty]

I kind of had my money on the orifice being the wrong size... hoped someone could check for me

meant to go back and get pressures/temperatures but life got in the way!

[seanf]

If its a Danfoss T2/TE2 expansion valve have a look at --> https://assets.danfoss.com/documents/DOC312122325735/DOC312122325735.pdf

Going by the condensing unit info youve got, for 32C ambient and -30C evaporating temp its 2.75kw of cooling.

What I get from looking at the selection of a Danfoss TE2, going with 45C condensing temp and -30C evaporating temp on R404a.

Using their capacity correction calculator for orifice size,

Capacity / (Subcooling factor X Distributor pressure drop factor)

- For the N range (-40C to 10C) -

With the worst subcooling of 2K gives Subcool factor of 0.97
And worst pressure drop of 2Bar gives Distributor pressure drop factor of 0.92
Giving a capacity of 3.08kw, so the lower end of a number 4 orifice but above a no.3

With the good subcooling of 15K and no pressure drop gives 2.37kw or the high end of no.3 orifice


- For the B range (-60C to -25C) -

With worst subcooling 2K and pressure drop 2bar gives 3.08kw or low end of a no.4 but above a no.3 orifice.

With good sub of 15K and no pressure drop gives 2.31kw or the higher end of a no.3

[Rob White]

Was it working ok before the compressor failed?
If it was then why would you assume it's the orifice ?
The only thing that has changed is the compressor and the fan.

I'd look to them first.

Rob

[knighty]

I ordered new orifices (3 and 4) when I made the thread, just waiting on delivery

had the gauges on it now, suction pressure is low, I think compressor might be cutting out on low pressure switch, but not 100% on that, didn't have time to sit and watch it.

takes forever to pump down on shutdown too.... maybe orifice is blocked? - I didn't remove the system from previous freezer myself, just put it up on this one



Was it working ok before the compressor failed?
If it was then why would you assume it's the orifice ?
The only thing that has changed is the compressor and the fan.
I'd look to them first.
Rob

this is a totally new (used) separate system from the original one, original one was the one on the box from when it was on the truck

and... it's just kind of a gut feeling, I can;t remember the temperatures/pressures etc. from setting it up (brain injury) something just didn't feel quite right.... but with an ambient temp room and evap missing a fan it was more of a gut feeling than any real science behind it

left it to pull the temp down so I could go back and look again, but crazy bush here with everyhting going on in the world right now, haven't had a chance

[RANGER1]

Is fan fixed, as that will cause low suction pressure

[redroge]

Faulty Tev power element ?

[charlie patt]

I would suggest restricted or bad tev if could is not frosting and suction line is tev is bypassing probable got crap from comp in it just make sure it matched to units