Freezer temperature problems

[DaiB]

Some advice please, thanks for all replies.

Have a 90 litre freezer built in with Danfoss 35 compressor, sintered bronze keel cooler, 20x80 U shaped evaporator. Top load. F135a

Running for first two months of the season at set point of -10c and compressor running about 50% of the time.
Few weeks ago it started struggling and could only manage -6c with compressor running full time.

Dived down and cleaned the keel cooler and that helped for a while but as the sea water. temperature increased the performance continued to fall off.

Turned it off and allowed it to cool down to ambient and left it for a week.

Had a fridge guy down and he ran the system and checked the suction pressure and said the gas was fine.
Left it on and when it got down to 3c it would not cool down anymore.

Let it cool down for a day and then recorded the following.

Start. Temp 29c
30 mins. temp 15c. light frost on first 12 inches of suction pipe after evaporator.
60 mins. temp 9c. light icing for 8 inches
90mins. temp 3c. ligth icing for 2 inches.
120 mins. temp -1c. light ice for 2 inches
150 mins. temp 1 c. no iceing
180 mins. temp 3 c. no iceing

During above compressor run full time. Sea water temp 27c

Undercharge? Overcharge?

Any advice please.

 

[vyv_cox]

You can find a page on my website about interpreting the position/absence/excess of ice on various parts of the installation. Written by my son Owen who knows all there is to know about the topic.

 

[superheat6k]

You mention F135a - did you mean R134a ?

I would say it is undercharged, so suggests it has been losing refrigerant for a while, so a tiny leak somewhere. Check for oily marks on the pipework, especially around any couplings. Then check with a 50:50 solution of washing up liquid applied to every joint with a small paint brush. Apply the fluid generously and see if any small bubbles appear. Really small leaks appear as a small ball of flossy bubbles.

What is the discharge pipe temperature and temperature from the keel cooler back to the evaporator before the capillary tube ? If it is undercharged the discharge will become cooler. Ideally to really check the suction and discharge pressures are needed - do you have gas charging points anywhere ?

However, with seawater at 27oC, I would expect the discharge should be distinctly hot, e.g. above 70oC. The pipe leaving the keel cooler should be around no more than 40oC.

Another possibility is that the compressor is faulty and simply not pumping effectively. Does it sound OK ?

 

[DaiB]

You can find a page on my website about interpreting the position/absence/excess of ice on various parts of the installation. Written by my son Owen who knows all there is to know about the topic.

Vyv, thanks for your reply and thanks for doing this website. Have read through the fridge section and it looks like undercharge.

 

[DaiB]

You mention F135a - did you mean R134a ?

I would say it is undercharged, so suggests it has been losing refrigerant for a while, so a tiny leak somewhere. Check for oily marks on the pipework, especially around any couplings. Then check with a 50:50 solution of washing up liquid applied to every joint with a small paint brush. Apply the fluid generously and see if any small bubbles appear. Really small leaks appear as a small ball of flossy bubbles.

What is the discharge pipe temperature and temperature from the keel cooler back to the evaporator before the capillary tube ? If it is undercharged the discharge will become cooler. Ideally to really check the suction and discharge pressures are needed - do you have gas charging points anywhere ?

However, with seawater at 27oC, I would expect the discharge should be distinctly hot, e.g. above 70oC. The pipe leaving the keel cooler should be around no more than 40oC.

Another possibility is that the compressor is faulty and simply not pumping effectively. Does it sound OK ?

Superheat6k,, thanks for your reply.
I have done some more tests.
Set thermostat at 5c and it runs fine, about 20% time running.
Set thermostat at -6c. BOX 24c, Sea 25c
+60mins box11c, light frost for 12" on suction pipe. Compressor about 50c at discharge pipe. From keel cooler to evaporate about 30c.
+120mins box 2c light frost on suction pipe for 6inches. Compressor about 55c, keel cooler out about 30c
+210 mins box -3.6c no frost
+240 mins box -2c no frost.
Compressor run 100%. Load 4amps approx.

There is a charging point on suction side but no high side connection.

The compressor sound same as normal to me.

As a result of above assume lack of gas or compressor performance? Do you think this is correct?

ref gassing: is the r134a as sold in small canisters for auto ac system top up suitable for this job or is it no good due to oil added with the gas?

Thanks for your time and answers.