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bjkmiami
19-02-2014, 09:59 AM
Hi folks again...
honestly we are tyring to figure out some specific problem which leads me to such questions..So what happens if your system components are not choosen accordingly..meaning that your evap. OR your comp. OR your condenser is oversized or undersized for the particular design condition.....
thx in advance....

passandscore
19-02-2014, 03:04 PM
You say that you're trying to figure out a specific problem. What's the problem?

If your system components are not sized properly many things may happen. I suggest you review the following.

http://www.hvacrinfo.com/Cope_manuals/AE104_R2.pdf
(http://www.hvacrinfo.com/Cope_manuals/AE104_R2.pdf)

The Viking
19-02-2014, 04:48 PM
A refrigeration system is a closely balanced system, anything upsetting that balance will affect the performance and reliability of the system.

As to your openended question...
What will happen if I cut this cable?
As you might guess, just as you need more information in order to answer my question, we need more information to be able to answer yours...

:cool:

bjkmiami
20-02-2014, 08:39 AM
A refrigeration system is a closely balanced system, anything upsetting that balance will affect the performance and reliability of the system.

As to your openended question...
What will happen if I cut this cable?
As you might guess, just as you need more information in order to answer my question, we need more information to be able to answer yours...

:cool:
well we are having flood back problem...we have replaced the TXV and still have some liq. coming back...evap capacity is matching txv but compressor is bigger..so can this phenomena cause such problem??? thx....

RANGER1
20-02-2014, 11:04 AM
So what's the Tx valve on?
Give us some pressures in system, room or water temps, refrigerant type etc etc.

If TX valve is sized correctly then either there is no heat transfer due to poor air flow or ice build up or something like that.
If suction pressure is to low because compressor is to big won't necessarily mean flood back.
Liquid/suction line heat exchangers are renowned to leak internally as we'll.

bjkmiami
20-02-2014, 12:45 PM
So what's the Tx valve on?
Give us some pressures in system, room or water temps, refrigerant type etc etc.

If TX valve is sized correctly then either there is no heat transfer due to poor air flow or ice build up or something like that.
If suction pressure is to low because compressor is to big won't necessarily mean flood back.
Liquid/suction line heat exchangers are renowned to leak internally as we'll.

hi there..thx for the reply...
system runs off R404A with ZF40 K4E copeland scroll compressor. Exp valve is Alco TCLE 600SW40 with solenoid right before it(Alco 200 RB 6T5)
design conditions are -25C evap / 45C condensation....

Rob White
20-02-2014, 01:05 PM
.

Hi bjkmiami.

We need more information.

To be able to work out if there is a mismatch we need to know
far more information.

How old is the system?
How long has it ran?
Has it ever ran correctly?
When did it start to not work correctly?
What has changed?

What is the suction pressure / temperature?
What is the discharge Pressure / temperature?
What is the temperature of the air onto the heat exchangers?
What is the temperature of the air off the heat exchangers?

Then we may be able to talk about it.

Regards

Rob

.

frank
20-02-2014, 03:20 PM
How have you determined that it is liquid floodback?

Is it because the suction line is frosting or do you have zero superheat?

bjkmiami
20-02-2014, 04:04 PM
How have you determined that it is liquid floodback?

Is it because the suction line is frosting or do you have zero superheat?

well we have seen an extensive bubbling inside the crankcase of the compressor with the oil...and this was not during start up!!!!and yes superheat was also lower than what is set on the TXV!!!

passandscore
21-02-2014, 04:21 AM
Is the oil foaming up and staying that way or does the oil clear up? Do you have a crankcase heater? If so, is it working? How often does the compressor cycle off? What is the temperature of the room that the compressor is in? Perhaps off cycle migration is a problem!

I would start by answering the questions asked by Rob White. Without the numbers, we are simply speculating.

bjkmiami
21-02-2014, 09:54 AM
Is the oil foaming up and staying that way or does the oil clear up? Do you have a crankcase heater? If so, is it working? How often does the compressor cycle off? What is the temperature of the room that the compressor is in? Perhaps off cycle migration is a problem!

I would start by answering the questions asked by Rob White. Without the numbers, we are simply speculating.
well what i saw was bubbling and clearing up afterwards from time to time...and i dont think crankcase heaters work while comp is running and this was not a start up!!!!! the room temp was -20C at the time..
thx...

Gary
21-02-2014, 01:32 PM
The following data would provide a much more accurate picture:

Evaporator air/water in temperature = ?
Evaporator air/water out temperature = ?
Low side saturation temperature = ?
Suction line temperature = ?

Condenser air/water in temperature = ?
Condenser air/water out temperature = ?
High side saturation temperature = ?
Liquid line temperature = ?

Gary
21-02-2014, 01:55 PM
superheat was also lower than what is set on the TXV!!!

Seriously? You are not even going to tell us what the superheat was (let alone the saturation and suction line temperatures)?... just that it was lower than the TXV setting?

bjkmiami
21-02-2014, 02:24 PM
Seriously? You are not even going to tell us what the superheat was (let alone the saturation and suction line temperatures)?... just that it was lower than the TXV setting?
hello gary...
well TXV superheat setting was supposd to be 7K we even increased it to 10K at some point but when we measured at the compressor suction we have seen diferent superheat at diferent times..such as 3K 5K 8K.....Couldnt get to the evaporator since the room was loaded badly but they have another unit running in the same room soo they r OK now soon we ll go there again to check on all those parameters u mentioned!!!
Suction line temp (lowest -22C highest -15C)
evap temp -25C
condensation cycle between 30C to 45C and unfortunately i dont have the other parameter at this moment!!i ll try to get it all next visit..
and thanks for your time!!!

Gary
21-02-2014, 02:43 PM
An oversized compressor will make flooding less likely, not more likely.

If the TXV has the proper orifice, then the most likely cause of hunting would be insufficient airflow through the evaporator (low heat load). Second most likely would be gross refrigerant overcharge.

If the superheat at the compressor inlet is lower than the superheat at the evaporator outlet, then liquid refrigerant is somehow entering the suction line (suction/liquid heat exchanger leaking internally?)

joe-ice
21-02-2014, 03:52 PM
Also might be worth looking at the txv feeler bulb for good thermal contact with suction line and in correct position and insulated.Have seen hunting caused by loose feeler bulbs.