Cellar cooler freezing up

Hi.
I have been recently called to a cellar cooler system, (below ground,) in a hotel with a Searle evaporator coupled to a Prestcold 1 HP semi, that has been installed for years but has suddenly started frosting up. The thermostat appears to operate correctly and is cycling around 12 degrees. There is no defrost cycle and the evap fan stops every cycle. The unit is fully charged, the fins are totally clean. The fan is running at the correct speed. The superheat is correct and the expansion valve is feeding the coil evenly. No one has changed the stat setting or increased the size of the room, but for some reason the coil seems to ice up solid including the suction line. There is a suction line heat exchanger which I don't think has collapsed internally. This system is on R12 and is evaporating at about -1 degrees when the room is at 12 degrees.
Has anyone any ideas?
I have had this happen to me before at other sites and cannot find anything wrong.
I end up fitting a defrost clock and it solves the problem. Any suggestions would be greatly appreciated.

Maybe a problem with the expansion device, TXV/cap line.

Has the humidity in the cellar changed at all?

has this happened when the outside/ambient changed,affecting the humidity the heating in the pub cranked up staff leaving door open,are the fans running all the time compressor not stopping is it a pump down system?.

This is just a function of the ambient and a bit of bad luck.
If Evap temp -1C then would not freeze up.
Does the cellar have some other type of cooling equipment in (self contained inline cooler)
If yes, at night when pub is busy this will be running keep the cellar warm, cellar cooling running (more than likely cycling) As the ambient is cold cond pressure is going to be low, thus the suction pressure (evap temp) is going to be low. Once it starts to freeze, then theres no stopping it, especially as the fan is turned off in the off cycle. If a defrost clock works for you, then thats OK, there are many other ways to sort the problem.

Quote:

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Originally Posted by Pykester1

There is no defrost cycle and the evap fan stops every cycle.

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The evap fan should run continuously. This defrosts the coil in the off cycle.

it is normal on celler cooling to get yeast groth on the evaporaterfins this grows and should be cleaned off to get full cooling without frost forming this is more common in cellars which store traditional beers

Get the evap fan to run all the time, and see what happens - should be fine.

Andy

Thanks for all your input. System is not on pump down. Customer does not want fan running continuously, ( it has always been that way.)
Have replaced expansion valve and problem has not yet reccured.
Ambient outside cellar has changed, (indoors I mean.)
Customer's basement central heating has been off for repairs and he said it has been much colder outside the actual cellar room for the last month.
I did think this and the expansion valve may be the problem but I was interested in other people's opinions and experiences.
Once again, thanks for the input.

Evap fan should run all the time,,,,

:D

Quote:

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Originally Posted by lawrence1

Evap fan should run all the time,,,,

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:cool: i agree, with the evap fan running all the time , this will help keep the evap coil clear of ice , once the cellar has reached the required temp and the t/stat switches of the condensing unit . worth checking that the evap coil does not need cleaning . :Dwe clean loads of coils with coil cleaner . improves the way the work no end . and saves the customer money .( reduced running costs ) :off topic:oh one quick thought , the beer delivery men , do they turn off the evap fan when they make the beer delivery . AND NOT TURN IT BACK ON WHEN FINISHED . ive come across this loads over the years . by the the time the publican has noticed the evap is really iced up . turning the evap motor back on will not clear it . just a thought

Door seal stuffed.

Sedgy, yes it is normal. Coldstores including Beer cellars (and fridges) which are used to keep a product which is in effect still 'alive' and is progressing through the ripening and rotting process, is subject to bacteria from the product forming in the coldest place. In the case of beer, it is the yeast and/or hops, and can cause horrendous growth on the evap fins if left unattended. Fruit is also a major culprit and you will find a different strain of bacteria (very dry) on the fins of a greengrocer coldstore. Fresh products are also the cause of domestic FF drain lines blocking up. And lastly, be aware of the damage vinegar (acid) can do. Restaurant chefs often make up dressings and sauces, keeping them in the fridge. Some of these may contain corrosive vinegar acid which will - in time- put pinholes in the copper evap. Changed plenty of Foster and Williams evaps due to this.

ok fridge doctor,
as you say all info is usefull.