Everything seems right but not freezing? Old Style with fuzzy logic

[teemyob]

Hi,

Despite 30 years of experience, I am struggling with something that is driving me mad.

I have a customer with an AGA upright frost free freezer (commercial style domestic).

It has electronic control with reverse gas defrost. All that is working fine, its just not refrigerating.

The system is fully charged (has been evacuated and recharged with R134a). It was probably charged okay to begin with.

The running back pressure is just above zero, this indicates an evaporating temperature of around -23c.

As its a freezer, I was expecting and evaporations TD of around 10-15c. So therefore, I initially expected a back pressure of -10psi(g).

Speaking to colleagues, they suggest the back pressure of around zero is okay?.

Please can someone help me out here?

Regards,
TM

[seanf]

Fin tube evap coil with fan?
Capillary tube or expansion valve or EEV?

[RANGER1]

Hi,

Despite 30 years of experience, I am struggling with something that is driving me mad.

I have a customer with an AGA upright frost free freezer (commercial style domestic).

It has electronic control with reverse gas defrost. All that is working fine, its just not refrigerating.

The system is fully charged (has been evacuated and recharged with R134a). It was probably charged okay to begin with.

The running back pressure is just above zero, this indicates an evaporating temperature of around -23c.

As its a freezer, I was expecting and evaporations TD of around 10-15c. So therefore, I initially expected a back pressure of -10psi(g).

Speaking to colleagues, they suggest the back pressure of around zero is okay?.

Please can someone help me out here?

Regards,
TM

TM,
First, a TD of 10 to 15Deg C is out of the question.
More like 3 to 4 deg C.
So with -23 deg C suction, expect at least around -18 deg C

You say not refrigerating, so what is current temperature?
If you measurer air on/off you can tell if it is doing anything.
Is evaporator definitely defrosted?
Is door seal sealing correctly

[frank]

R134a with a capillary expansion device can become blocked (oil flocced) over time.

Although you have low temps on the evap I would suspect that with a blocked capillary, you have restriced flow and a starved evaporator leading to high temps in the box.

[teemyob]

Fin tube evap coil with fan?
Capillary tube or expansion valve or EEV?

Capilliary Tube

[teemyob]

Sounds feasible

[teemyob]

TM,
First, a TD of 10 to 15Deg C is out of the question.
More like 3 to 4 deg C.
So with -23 deg C suction, expect at least around -18 deg C

You say not refrigerating, so what is current temperature?
If you measurer air on/off you can tell if it is doing anything.
Is evaporator definitely defrosted?
Is door seal sealing correctly

Thank you

Slight sweating on fin evaporator
air off barely lower than room temp
door 100%

[chemi-cool]

I totally agree with Frank. Its blocked somewhere.
Bear in mind that R-134 is a fantastic cleaning agent and have more blockage problems then most refrigerants.

Can you install a TXV instead of the capillary tube ?

[teemyob]

I totally agree with Frank. Its blocked somewhere.
Bear in mind that R-134 is a fantastic cleaning agent and have more blockage problems then most refrigerants.

Can you install a TXV instead of the capillary tube ?

hi, thanks everyone.

Sadly no room!

[seanf]

What about a fixed orifice?