Wittenborg Chiller Vending Machine

[Pete L]

I normally work on vehicle aircon, but got asked if i would look at Wittenborg that was not working. Both the cond. and evap fans were shot so I fitted a pair of Elco replacements today.Compressor runs and has one service port that my R12 gauges fit. service port is on lp side I believe. Static pressure was 40 psi today and when running, pressure was 0 psi. Compressor is a Danfoss unit SC12B showing R12 / R 502 ( I assume that means it can use either). My reaction was that it was low on refrigerant, so having some RS 24 (used as a drop in replacement for R12) around I added 200gms - I've no idea system capacity. Pressure when running increased to 5 psi, but still no cooling and now small capillary pipe into evap iced up in double quick time.
I suspect that there may be a blockage in HP capillary line - is this likely or even possible? How can I fix this and if i am way off beam, what is happening and how can I fix it? Any help much appreciated, but bear in mind this is my first non vehicle refrigeration effort so don't take anything for granted!!:confused:

[Brian_UK]

Hi Pete and welcome to the forum.

I hope that you didn't just add your RS24 to the system.

You DID recover the R12 first ??

In the absence of a data plate showing the system charge weight then you could try charging to sub-cooling as it is a capillary based system.

The static pressure needs a related temperature to be informative.

[Pete L]

thanks Brian, interesting site, hope I can keep up!

Re RS 24, no I did not recover R12, machine is pretty elderly and customer wanted an idea of problems and cost to fix. This was just a quick shot at seeing if it would cool before he agreed either to repair or scrap. I did not find label with Danfoss info until after I put refrigerant in - it was a compromise just to see if anything happened.
Temp was 19C when I did this.
Now the good bit, how do I charge to sub cooling and what does this mean? Normally, I have all vehicle info before I start.
Any idea why it would be icing up though or is this to be expected?

[Brian_UK]

Probably icing up because it is short of refrigerant although it could be a blockage.

The rules now state that if it is R12 then the first thing you must do if you are going to repair it is:-

Reclaim the refrigerant and send it back to your waste handling people for destruction.

Find and fix the leak.

Now you can think about getting it going.

Try blowing through with OFN to clear any blockages.

Replace the filter drier, if it's an old copper spun one then it is quite possible that the internal sieve has failed and bits are blocking the capillary.

Vacc it and recharge with a drop-in R12 replacement.

Charging to sub-cooling:-

Fix a temperature probe to the outlet of the condenser so that you can monitor the liquid temperature leaving the condenser.

Compare that temperature with the discharge gas pressure temperature.

Keep adding refrigerant until you have something like a 5°K differential. This then means that you have liquid entering the capillary.

Or, just tell the fella that it's shot and he needs a new one :)

I suppose it does depend on the unit but it may be possible to install a new condensing unit complete, some machines use a cassette system, I don't know whether your has this type or not.

[Andy W]

I repair a lot of vending machines, actually have one on my bench as we speak. The common leak is on the vapouriser line which runs inside of the drain pan, a visible check will show if this is suspect, also look at the end passes of the evaporator and check if they are corroding, I have had a few evaps rotted but mainly vapourisers or leaking charging ports, definately test with OFN, there is no other way to be certain.

Regarding charging one up they very rarely have a data plate with gas charge on, if using R134a I vapour charge just until the last pipe of the evaporator is wet before the accumulator, I sometimes fit a cardboard box on top of the machine with a flexi duct pipe to give me a air off / air return if I have problems getting the gas charge right.if you use a gas that needs to be charged via the liquid phase, fit an high side fitting in the liquid line and liquid charge 150 gm of liquid using a liquid atomiser to charge the low side but carefully does it.

[Dr._Fleck]

The no nonsense way to charge capillary systems:

Just put loads of gas in until the suction frosts, let it get down to temp and then keep 'reclaiming:eek:' a bit of gas until it stops frosting back.

[Pete L]

Dr Fleck/Andy W - thanks for the comments. Andy, given that I got a static pressure just by putting gauges on the service port and then added 200gms, could I have overcharged the system? Put another way, what charge weight would you expect a typical wittenborg to take? Pipework generally looks good externally. I've not tested with OFN yet as I'm just trying to find out if machine will actually run.If it will run then I will pressure test and repair conventionally - assuming customer will pay for it!

Dr Fleck, capillary pipe going into evap was heavily frosted but temp did not come down at all - it did not cool down initially and then warm up either as if capillary had iced up. That's why I wondered if system had blockage.

Comments please.

[The MG Pony]

SC12B is a 3,000 BTU R-12 compressor, I doubt it would live long at all with R-502. It should have an HST kit on it.

[Sledge]

Hi

I am still stuck at the beginning. I have never encountered a system that is able to handle R12 and R502, interchangeable. It is one or the other. You have approached the issue assuming that R12 will be ok, and have used an R12 replacement refrigerant. I think that you need to establish which refrigerant first.

I would get the manufacturer, model number and serial number of the compressor, and the unit and try and search what refrigerant the machine is suppposed to have. I attempted to search the model number you have posted at danfoss.com, but they dont list it. You will need to get this information from a supplier, who has a cross reference sheet.

I am not clear what has made you suspect that the cap tube is plugged. It is a very common problem with the newer refrigerants, but it is something I almost never saw with R12 or R502.

I am not certain what is meant by OFN, we use nitrogen, to purge a system. I would attempt to purge through the system with nitrogen, and clear, or prove the existence of a blockage that way.

[The MG Pony]

I have the data of the compressor it IS R-12

UCBC0033RW**** (SC12B) 1/3Hp 3,2643BTU @ 45f evap 90f condencer, R-12

[Andy W]

To determine if you have a blockage, cut the capillary at the drier, add OFN and see if it bleeds through ok, when I change a filter drier I always blow through it to check if it is blocked out of habit, charging with loads of gas to get frost back or sweat back was how we did it years ago and then blew some gas off, which we dont do any more, right guys? so if you do it now with these new blends of drop in gasses which need to be charged in liquid phase, if you reclaim or blow off a bit you are then proportionally altering the mixture of the blend if you like and this will cause other problems.

Do you have a picture of the machine by any chance and is it a single or double evaporator model.

[Andy W]

I am not certain what is meant by OFN, we use nitrogen, to purge a system. .Oxygen Free Nitrogen.

[Pete L]

Andy W. I can take picture of machine tomorrow, and will then have to work out how to post it here! Machine has a single evaporator which runs about 3/4 height of machine at back on rhs as you face it.
It has no model number as far as I can see, but does have a serial no 232525, not sure if this will help or not.

[Pete L]

Thanks for the comments, I have now got to the bottom of it. I added more refrigerant and icing up stopped and evap got cold - system operates. I then removed refrigerant and pressure tested with ofn, the evap is leaking. Can I assume that trying to repair an elderly evap is not worthwhile?

[Chillin4alivin]

DONT GIVE UP NOW MATE!!

Repair evap and hopefully all will be good;)

[Andy W]

Thanks for the comments, I have now got to the bottom of it. I added more refrigerant and icing up stopped and evap got cold - system operates. I then removed refrigerant and pressure tested with ofn, the evap is leaking. Can I assume that trying to repair an elderly evap is not worthwhile?If the evap is made of copper, by all means repair it, dont take it for granted that there is only 1 pin hole leak you probably have a few usually around the brazed on return bend ends either the coopro leaking, rebraze with a coopro with a silver content or the copper is blistering, braze over the blisters, it may be worth adding a dye to it for future use. If the evap is gone in numerous places including along the length of the copper tubes, a new evap may be needed. The vending companies I do work for I ask them to get the evaps (usually from USA) and I then fit, failing that send the old evap to Beehive coils and they will make you one ............ for a price.

[Sledge]

Oxygen Free Nitrogen.


LOL! Thanks!

Cheers!

[taz24]

the evap is leaking. Can I assume that trying to repair an elderly evap is not worthwhile?


If time is not an issue go for the repair.
Evaps tend to leak on the return bends so remove a small section of the aluminium fins to access the copper and just braze up.

Then pressure test again and do a tripple vac (vac - purge with OFN. Vac - purge with OFN and finaly vac and weigh in some refrigerant).

To charge up if you do not know the correct weight.
Stop the evap fan from running and then charge up slowly, bleeding only liquid to the suction (not too fast, don't damage the comp).
Watch the suction line when frost apears and forms on the suction let it get to within about 6" of the comp then stop charging and start the evap fan.
You will have the right charge.

Cheers taz.

[Pete L]

Ok, thanks for all the comments, but more questions I'm afraid. The evap unit complete with compressor/condensor all slide out together as a "package" - certainly far enough to work on without a problem. I have identified 3 copper bends where there are leaks, but the copper bends are linked by aluminium pipe where the evap fins are. These ally lengths look like they may be crimped onto a short piece of straight copper before the the copper bends are soldered or brazed on. My feeling is that if I get near these joints with heat the ally will melt. Am I missing something here? Anyone got experience of repairing this type of evap?

[Andy W]

All my machines slide out as a packaged unit complete, not seen any alloy pipe on any vending machines that I have worked on, are you sure it is not just painted copper pipe like on the Williams evaporators? I have brazed stubs as close as 3" to an alloy crimped pipe, wrap a wet cloth around the join and braze quickly with an oxyacetylene torch, not too hot though and any doubts about the integrity of the alloy / copper joint, seal with super poxee.

Do you have a picture yet?

[Pete L]

Andy W. Am virtually certain pipes are aluminium, I put a file on one of them and it was very soft. Will check again Monday though to be on the safe side.

Did not take photo in the end as I got machine running. I can take photo, but can a picture be posted on this site? I looked at FAQ's and could find no mention of photos.:confused: