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Gaz22
01-02-2015, 10:47 PM
Has anyone worked ona space pack running r407f LT?
I got some glass door freezers struggling to run to temp and they alarm every couple of days, i heared the 407f is not a good gas to be used for LT.
The suction pressure is 0.9/1bar and discharge is 13bar.

Rob White
02-02-2015, 01:56 AM
Has anyone worked ona space pack running r407f LT?
I got some glass door freezers struggling to run to temp and they alarm every couple of days, i heared the 407f is not a good gas to be used for LT.
The suction pressure is 0.9/1bar and discharge is 3bar.

Are they discharging to HT compressors (compound) or is that a typo?

Rob

.

Glenn Moore
02-02-2015, 06:11 PM
Hi Gaz
I hope that discharge pressure is 13Bar not 3 Bar?.
What expansion valves are fitted and what are the superheats on these cabinets ?.

yorkshire
03-02-2015, 12:07 AM
check the glide setting in the case controllers

Silhouette
05-02-2015, 06:12 PM
0.9/1bar is not low enough for LT cabinet operation you need at least -35C evaporating condition for FGD cabinets!

Gaz22
05-02-2015, 06:22 PM
Are they discharging to HT compressors (compound) or is that a typo?

Rob

.

Hi yes its a dual temp pack

Gaz22
05-02-2015, 06:36 PM
Hi Gaz
I hope that discharge pressure is 13Bar not 3 Bar?.
What expansion valves are fitted and what are the superheats on these cabinets ?.

The suction is 1 bar, the discharge is 11 bar.

Its a carter glass door freezer 3 freezers next to each other with only a plastic divider between them and 3 doors on each freezer.
They are fitted with thermostatic expansion valve and super heat is 4.2 for first freezer, 6.4 for second one and 6.5 for third one. At the time those reading were taking, none of the freezers had any alarms. But super heat on the 3rd cabinet gets to 8/11 and temp goes down to -15 when it alarms
The first one never alarmed since install over 2 years ago.

Gaz22
05-02-2015, 06:39 PM
0.9/1bar is not low enough for LT cabinet operation you need at least -35C evaporating condition for FGD cabinets!

I know but when the pack is setted to lower pressure it keeps tripping on lp on a cold day so they raised it up.

Rob White
06-02-2015, 11:26 AM
.

Higher superheat means less liquid in the evaporator (for whatever reason).
If the evaporator is being starved for any reason then that might cause this.

If it is cutting out on LP in the cold weather and if you need the systems
to run lower than it is, somebody needs to correctly commission the whole
pack and set it up as it should be.

Sometimes on packs if there is an issue with liquid distribution then individual
cases suffer and it tends to be the same cases. You need to establish
when the cases alarm and what is happening on the pack when that happens.

Just adjusting a control to stop an issue is not the real answer and can lead
to other problems.

Rob

.

Rob White
06-02-2015, 11:33 AM
.

Have you ever had any leaks on the system in the 2 years that
you say it ran ok without any alarms? 407 fractures if it
leaks and the results can be very confusing if you have never
encountered it before. Weird pressures and abnormally low suction
pressures compared to new virgin refrigerant.

R407f is blended R32, R125 and R134a.

The 134a tends to leak out first and you are basically left with R410a.

Has this pack ever lost refrigerant over the last 2 years?

Rob

.

Peter
26-02-2015, 02:37 PM
The 134a does not separate out from the other two components. Depending on where a leak occurs, the three components may leak out in different proportions from the original composition. It is usual that the higher pressure components leak in a greater percentage. This would make 407 blends richer in 134a by a few percent and you could expect to see a small loss of capacity. Topping up usually restores the blend back to specification. At lower temperatures it is more important that glide is taken into account when setting the TXV.

Glenn Moore
27-02-2015, 03:22 AM
Are the expansion valves made for R407F or is this a retrofit job using R22,R404a, or R407c expansion valves, if the valves are not specifically made for R407F then the valves will never function correctly due to their Static Superheat curve will increase the Superheat control of the valve, the lower you go in evaporator temperature .