Freezer not pulling down to Temp

[ferret82]

Hi There, this is my first post so i hope that i have put it in the right section. I am only new to the refrigeration area i know some basics but need help. I have a freezer unit which has the following

HP = 2100Kpa = 49 Degree Celsius
LP = 250Kpa = -19 Degrees Celsius

I have found on the

outlet of my condenser the temperature is 46 Degrees C
and the Outlet side of my evapotor is -5 Degrees C

I used this to find my superheat / Sub cooling which ending up being

49 - 46 = 5
19 - 5 = 14

The ambient temperature where i work is about 45 Degrees C at the moment and the refrigerant is R404a
My problem is that the compressor will not pull the freezer down to -20 it gets to about -18.7 degrees C and just continues to run.

Can anyone help me in troubleshooting this and give me some where i need to look to fix this problem.

Thanks

[nike123]

Question is, is that system designed to work with such high outdoor temperature.
If yes, you are probably slightly low on refrigerant!
Subcooling is not 5K, it is 3K (49-46=3).
Check this post for more information:
http://www.refrigeration-engineer.co...97&postcount=3

[paul_h]

There might not be a problem. If the freezer is -18.7C, that might be the best it can do in 45C ambients.
Try cleaning the condenser, (with the power turned off), if it's in a kitchen it might need degreasing too.
If the freezer gets to -20C when the temp is cooler (and you've cleaned the condeser), then you have just found the limits of that freezer as far as ambients.

46C is what the best equipment in australia is rated too, and odds are what you have there might only be rated to 40C or 43C and is undersized.

Obviously if it gets to -20C just fine when the weather is cooler, that's the issue.

[Gary]

The SCT is only running 4K above ambient, so condenser sizing is not the problem.

The subcooling is low and the superheat is high. The system is short of refrigerant.

Add refrigerant until the subcooling is about 8.5K. If the superheat is still high (with the freezer near design temp), then there is a restriction, most likely a plugged TXV inlet screen or plugged drier.

[SULTAN]

I had the same exact problem and now i solved my problem. Thanks GUys

[fri11j]

before u got too far.. Is it tx or capilliary? you may find that superheat issues may be related to the space temperature, as you will find that the superheat maybe too high until the cabinet is at correct operating temperature, as capilliary systems are a fixed metering device and obviously cannot adjust due to variables in heat load.