Double check needed

[Latte]

Hi Guys,

Got a call out today, Message was "Dairy case high temp since engineer fitter TEX last week"

Just the call i like

The story so far, Check the enginners paperwork and indeed he replaced the expantion valve. The unit is an OLD !!!! Craig Nicol 12ft dairy with a copeland scroll condensing unit. Gas looked very low, hp 120 lp 10 nothing in sight glass. Leak tested coulnt find jack so topped up but was too busy looking at sightglass and overcharged. Now running at 300 HP and 60 LP. Sightglass however still flashing like mad and not flooding back. Check exp valve and frosting coming out but nothing at the other end of the coil on the knuckles. Tried adjusting valve at quarter increments, eventually had valve wound right out (5 Turns) still nothing. Check drier looks/feels OK only 0.1 degree C diff temp wise on the pipes and that might just be where i am holding the probe. Pumped down check the orrifice (No 4) no signs of burning and filter clear.

The only thing i can think is that the new exp valve is u/s. It is a Danfoss TES2 (R404) and is the same as the old one that was taken out as the old one is still there.

I plan to go out tommorow, pump down, change valve, Change drier, Vac out and see what happens.

I question is can anyone else thing os anything else that i may have overlooked


Regards

Raymond

[chemi-cool]

Hi Raymond.

High Pressure and non stop flashing is usually related to Condensing problems.

Check that area and see what you find.

Chemi

[dallan]

Raymond

I only seen it happen once or twice but is it possible that the previous engineer charged the system with R404a vapour.

[Latte]

Thanks Guys,
Finally think i have sussed it 3 hours later.

Got to site today, pumped down lowside, changed exp valve & orifice, changed drier and blew out and washed down condenser.

Tried to vac out only pulled 10" vac. Fairly sure there was no leak to atmosphere as i have leak check the other day so run the system up. These are the readings i got

Case temp 14 degrees
Ambient air into condenser 28
air out of condenser 38
Comp Discharge temp 82
Drier 38 Both Sides
Liquid line into TEV 24
" " out of TEV 4
Evap coil outlet (P4) 13

Thought it was strange, still didnt seem to be getting enough liquid to the coil, tried to pump down the pot, Shutting suction valve & oil pipes and HORAY !!! the pot only would pull into a 15" vac and i took 30 seconds to do that. Also as soon asi switched it off the compressor went bang and the suction shot straight up to 20psi. I assume either a bypass valve or the valve plates are letting by. I have ordered a new compressor but don't think it a current model so may be a little while getting one.


Regards

Raymond

[Latte]

Hi Mark,

I Cleaned the condenser to make sure that there is no blockage at all. The drier is new, its had two expansion valves, both been wound right out but still the coil does not seem to be getting enough liquid.
Now it a fairly old system so it's not a case of the condending unit being underpowered or anything so what else is there.

Poss LLSV not opening properly

I am confused on this on, my head is begining to hurt


Regards

Raymond

[homelover]

You cant pump test a scroll compressor as the have a bypass inside,

It seems to me like liquid starvation,
Is there a Heat exchanger is so it's probably crushed,
Had this loads of times on coldrooms it can catch you out everyone starts changing the tev's to no avail.

you can always stick a 3/8 sightgass in before the tev this will prove liqiud starvation.
All the ones I have done It has been obvious due to the temp change in the liquid line.

Homelover

[Gary]

Pressures don't mean much if we don't know what refrigerant you have.

You haven't provided nearly enough information to do anything but take a wild guess at what the problem might be. My wild guess would be a restriction between the drier and the TEV.

[Latte]

Sorry Gary

R404a.

As far as i can see there is not enough liquid getting to the coil, Obviously some IS getting there but it is a very big dairy to fill the evap.

Dont know if the unit has a heat exchanger or not but i was thinking about removing the LLSV to see is that was causing a restriction, what do you think.
What other readings should i be looking for ?


Regards

Raymond

[Peter_1]

If you have a pressure drop, then you could measure also a temperature drop.

Is the orifice correct sized?

When I install a new orifice in a TEV, then I always check if the orifice is +/- 1 mm from the seating. You then can push the seating of the orifice +/- 1 mm against the spring into the TEV
You should feel a little spring resistance when pushing complete in the TEV.
If the gas in the bellow is gone, then it goes straight in the TEV housing without any resistance.
(Jeeezzzz, what a difficult explanation)

[Latte]

Hi Peter,

The diary is a 12ft unit with a danfoss TES2 Expansion valve,
I didn't change the first one but the second time, when i went out to it i cahnged it like for like and also chacged the orrifice again for a No4.

According to one of our guys, a normal rule of thumb is length in meters equals orrifice size eg 1m=No1 4m=No4
Is this correct, i know someone will come up with a major technical equasion to work it out but a simple one would be nice


Regards

Raymond

[Peter_1]

Seems that a 4 should do the job.
I have here +/- 6 kW for 12 ft, so...seems OK.

Is egalisation of your TEV not blocked?
What type of compressor do you have Raymond?

[Andy]

Hi Raymond
just a thought, has someone by chance fitted a MOP type valve or is the phail placed somewhere it can't get a proper supheat reading, maybe reading liquid comming from one pass of the coil, or would the distributor be partially blocked.
Anyway by first guess would be a liquid line blockage, TD will give this one away.

Kind Regards. Andy

[Latte]

Hi Guys,
Thanks for all the replies, first to answer a couple of questions.
1) Copeland scroll Peter, cant remember model
2) I assume when the original valve was done it was replaced like for like, certainly when i repaced it again i cleaned down the pipe from the evap with wire wool so i should get a good reading and placed the feeler bulb at the 2 o clock position, if that makes sense.

Hopefully i can get back there and spend some time on it.

Regards

Raymond

[Gary]

Sorry Gary

R404a.

As far as i can see there is not enough liquid getting to the coil, Obviously some IS getting there but it is a very big dairy to fill the evap.

Dont know if the unit has a heat exchanger or not but i was thinking about removing the LLSV to see is that was causing a restriction, what do you think.
What other readings should i be looking for ?


Regards

Raymond

Low side:

Evap air in temp
Evap air out temp
SST (saturated suction temp)
Suction line temp at coil outlet
Suction line temp near compressor

High side:

Cond air in temp
Cond air out temp
SCT (saturated condensing temp)
Liquid line temp near condenser
Liquid line temp near TEV

[Peter_1]

Hi Guys,
.....ould get a good reading and placed the feeler bulb at the 2 o clock position, if that makes sense.

Hopefully i can get back there and spend some time on it.

I think I explained it wrong: i was talking about the external pressure equalisation line of the TEV, not the sensing bulb.