Double door Freezer temp issues

[Chopper86]

Hi,

I had been trouble shooting a 6 ft upright standing double door freezer at a Thai restaurant. The Carel controller is set to -19 and it can only achieve -10 degrees at its best.

Previous techs have swapped the compressor, fitted new evap fans and to no improvement.

Ive checked:

Evap fans (x4) are all operations
Evaporator and condenser coils are clean/clear
Checked suction pressure at compressor and getting 20psig/-25 on R404A...

The system has a CPR valve and the press. before the valve is about 20psig ... then it goes up to 40 psig (-10) at intervals... then drops... back to 20psig... all the while the suction line does not feel very cold at all in a freeze cycle and only frosts over during hot gas defrost (indicating the CPR valve is doing its job?)

The lowest we have achieved is -14 and cannot get the desired -19 set point. The system is on capillary expansion, so should that signal alarm bells when theres a CPR valve fitted?

Your advice would be greatly received.

C

[1mikeefc1]

Freezing back when it's on hot gas operation ring alarm bells, I would look at the gas charge as if its not cooling properly down the suction and the comp is ok sounds like it could be short. Does the drier feel warm/cold/hot?

[Rob White]

.

If you are confident that it is correctly charged with the right refrigerant,
I would look at the back pressure regulator.

If it fluctuates, it could be holding the evap temperature too high.

Try opening the valve fully so the system runs at the lowest back pressure
and see if it runs ok?

The only other thing I would look at, would be the gas itself. Was the refrigerant
replaced for new when the comp was replaced? How long ago was the compressor
replaced? and has the condenser fan ever failed or the condenser blocked?

It is possible for 404a to burn out (degrade through over temperature) due to blocked
condensers or faulty condenser fans, but if you are confident the refrigerant is good and
you are confident there is the correct charge, I would look to the comp or back pressure regulator.

Regards

Rob

.