Cold Room Temperature not maintained

[wrajesh]

I have a Carrier 10 hp unit Model CRL-1000-DX R-22 Refrigerant with Bitzer compressor Model 4PC-10.2-40P to maintain cold room temp of -18deg.C. We are facing problem of maintaining -18deg.c. as the temperature not pulling down below -5deg.c. The suction/discharge pressure is 22/290 PSIG.

Please advice possible troubleshooting to bring the cold room temperature down to -18deg.C.

[monkey spanners]

Is it a new room? If not has it ever worked? What has changed recently?

How much product is there in the room and what temperature is it? (is it being loaded in warm?)

What condition are the insulation panels?

Defrost heaters stuck on?

What size is the room?

[The Viking]

R22 in a freezer? Asking for trouble...

But some info to get us started:
-Has this been running and reaching set point in the past? If so, has any changes been made?
-Discharge temperature?
-Liquid line temperature?
-Suction line temperature?
All taken at the same time as the suction and discharge pressures, the more accurate the better, preferable after the system reached a stable running state.




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[wrajesh]

Thanks for your reply. The coldroom is old and was running accurately till last month and reaching -18deg.c. The product is loaded at room condition and was kept for 24 hrs for freezing. The panel insulation condition is in tack and no moisture observed on panels. Recently the temp. problem started and we flushed the system, replaced the expantion valve and reommissioned the system. Since then the temperature is not pulling down below -10dec.C. The pressures are taken simultaniously and are as under -
Room Tem. - 4deg.C.
Suction pressure: 20 psi
Discharge pressure: 290 psi
Liquid line temp: 40deg.c.

Kindly give your inputs.

Regards, Rajesh

[The Viking]

OK,
So the sub cooling is ~13K so at the moment there should be plenty of refrigerant.

If you give us the other temps we will know more...

-Discharge temperature?
-Liquid line temperature?
-Suction line temperature?
All taken at the same time as the suction and discharge pressures, the more accurate the better, preferable after the system reached a stable running state.

.

[mikeref]

Heavy load and high humidity will cause the evaporator to ice up quickly. Expansion valve set correct? Right size orifice?
Crankcase pressure regulator checked?

[Len Fiddler]

20psi evap temp -20 C
290psi cond temp 54 C
Liquid line 40 C the above 14 C subcooling and low suction pressure looks like a blockage in the liquid line
Regards
Len

[benijoseph]

wesh,

In my opinion faulty exp valve,

regds,

[wrajesh]

Hi Everyone,

We have replaced the expantion valve with Danfoss TEX5, Orifice no.1 The operating parameters now observed are as under -

Discharge Gas temp & Press. 80deg.C/ 290 PSIG
Suction Gas Temp & Press -14.7deg.C / 10 PSIG
Liquid Temp at Receiver 50.5 deg.C / 280 PSIG
Liquid Temp before entering Exp. Valve 18 deg.C. (This may be because the liquid line is inside cold room hence temp is dropped)
Liquid Temp after expantion valve before entering to Evaporator. -8.5deg.C.
COLD ROOM Temp -14deg.C.

Currently the temperature is not going down below -14deg.C. As I SAID EARLEIR WE NEED TO MAINTAIN -18deg.C. inside cold room.

Please let me know your observtions/sugesstions

Regards,
WRAJESH

[Balakathiresan]

Hi,
The refrigerant evaporation temperature / compressor suction gas temperature should be less than the desired room temperature (-18°c)

[Len Fiddler]

The TEX5 + 1 is OK but the condenser pressure is too high what is the ambient temperature onto the condenser
Len

[The Viking]

Is there less charge in the system this time around?
Before you had a subcooling of 13K but now, somehow, it dropped to 3K.

The temperature drop across the liquid line is also worrisome, I would check if it is gradually over the length of the pipe or suddenly (for example across a drier). If suddenly then there is a problem.

Your superheat is 15K, which is way too high.
However, before you start to adjust the TEV you must ensure that there is enough liquid feeding it. The subcooling should be at least 6K and any blockages of the liquid line needs to be sorted




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[benijoseph]

wesh,

check the quality of the gas! pour some water over the cond if it is air cooled then check the reading?

regds,

[padraic]

discharge 290psig is very high for r22... air in system or blocked condenser or wrong pipe size