General Split Icing Up

[airefresco]

Been called out to a General split system that ices up. The unit is a ceiling mounted single blow type that has been installed (by another company) about 3 years ago. It´s worked fine, with no problems since installation. The client cleans the filters every couple of weeks. Three weeks ago the unit iced up. It´s done it a few times since then, so I got the call. It´s a random fault and the unit can operate fine for days without icing up. I was there last week and everything was fine, it was working perfectly normal.

I´ve looked through threads on here with people with similar issues and from what I can find is there a few reasons that would cause this,

Poor Air flow - Filters are clean, coil seems fairly clean, but surely it would ice up all the time if this was the case. This unit can run for days without freezing.

Gas Issue - Definitely not this, weighed in fresh gas and still the same.

Contactor sticking - Not this either, the unit had only ran for 30 minutes yesterday when it started freezing and the room temp was 25ºC, ambient about 23ºc. It froze up within a couple of minutes today of been switched on.

Low load - see above

Restriction - It´s got to be this surely? From what I can gather, there is a capillary tube and some sort of what looks like a drier, although I suspect it is not a drier as it is quite small. See image below. What is the drier looking thing and is the small capillary line the only metering device?

When I charged it up today it froze immediately then defrosted by itself after a few minutes, ran fine for about 10-15minutes then froze again for 5-10 minutes then defrosted again and so on. There is no pattern, it just completely random.

I started to get readings, but things change so quickly by the time I have one reading everything has changed, so they are useless.

Model number of the outdoor is AOG54FMAYT.

Any help much appreciated.

Thanks
paul..

http://img706.imageshack.us/img706/1594/bulldogu.th.jpg (http://img706.imageshack.us/i/bulldogu.jpg/)

[Brian_UK]

Can you inspect the pipework at the evaporator?

Is there any sign of frosting there?

Different make I know but some units may have a strainer in the pipework near the pipe connector (Flare?).

edit: Just checked with a service manual, yes it is a strainer in your photo, manual here...

http://www.ultimateair.co.uk/pdf/Jan%2007%20Update/Current%20Single%20Split%20Service%20Manuals%20Mar06/Under%20Ceiling%20+%20Universal%20Units%20Service%20Manuals/ABY54U%20Service%20Manual.pdf

[airefresco]

Thanks Brian the manual is really useful. So, the thing that is not a drier is a strainer and the small bit of cap tube is the metering device. From that then I would hazard a guess that the strainer is the most likely culprit followed by the cap tube. Do you agree?

There´s another strainer on the suction side but it freezes up on either side of that, so is it safe to assume that is OK?

thanks for the help.

Edit to say the indoor is a right bugger to get to. I would probably have to take the indoor down to get inside it or the pipework. but from the manual, it doesn´t look like there is anything there anyway.

[wallerboy76]

look for where the icing -up starts, that is normally a good place to check first !

[aircon50]

A couple of questions. What is the application of the unit - bar, restaurant etc. I ask this because we had a General ABG unit in a bar that started frosting. Nobody had noticed the reduction in airflow. Eventually we removed the unit, and when it was dismantled the evaporator was heavily contaminated with tobacco tar. Filters are cleaned frequently, but the smoke goes through them!
Where does the frosting start? Does it start at the outside unit, or at the inside unit?
All the best from Tenerife
Graham

[airefresco]

Yeah it´s a bar. The unit is mounted over the actual bar above a sort of shelf that runs right along the bar. It looks as if the shelf is holding the unit up, which means I wouldn´t be able to get the cover off to get to the drip tray without lifting the unit down. If you take the fan deck out, can you get to the coils that way?

EDIT: - I was lying before, It appears that the unit ices up a the suction line from the indoor unit first. It was switched on and running when I got there today, and everything was functioning. It started to freeze up after about 15 minutes of me being there and was pretty quick, one minute the suction line is sweating nicely, the next the whole suction line and accumulator was frozen.

I think I´m going to lift the indoor unit down and give it a good clean before changing parts. How do you get to the coils on these units?

[airefresco]

Been back today to try and clean the coil. I couldn´t work out how to get into the coil. I tried lifting the drip tray out but the front drops about 2cm and then will not move any more. I took 3 screws out of each sides and the 9 on the back behind the filters. I couldn´t see anything else holding it in place. I suspect I probably need to take the fan deck out to get to it, but I can´t do that without taking the whole unit down. I´m not convinced it is and airflow problem anyway. There´s a hole in the side of the unit for the clips on the cover and I shone a torch through there. I can´t see very well, but the coil looks fairly clean from what I could see.

The time it takes to ice seems completely random. If it was air flow surely it would ice up around the same time everytime the unit is used? Is there anyway I could prove what is causing the icing up?

thanks
paul..

[nike123]

Been back today to try and clean the coil. I couldn´t work out how to get into the coil. I tried lifting the drip tray out but the front drops about 2cm and then will not move any more. I took 3 screws out of each sides and the 9 on the back behind the filters. I couldn´t see anything else holding it in place. I suspect I probably need to take the fan deck out to get to it, but I can´t do that without taking the whole unit down. I´m not convinced it is and airflow problem anyway. There´s a hole in the side of the unit for the clips on the cover and I shone a torch through there. I can´t see very well, but the coil looks fairly clean from what I could see.

The time it takes to ice seems completely random. If it was air flow surely it would ice up around the same time everytime the unit is used? Is there anyway I could prove what is causing the icing up?

thanks
paul..

You should measure and monitor air speed/flow at outlet of indoor unit (and air delta t) to see if it changes when frost start to form, in order to eliminate air flow problem.

Also, I would check 4-way valve.

[airefresco]

I don´t have anything to measure airflow. If I took the dT when the unit was operating normal and then again as soon as the frosting starts to form, would that suffice? For example if the dT was normal and then there was a big sudden change just before or during the ice forming, is it then safe to assume there is some kind of intermittent restriction somewhere?

[nike123]

I don´t have anything to measure airflow. If I took the dT when the unit was operating normal and then again as soon as the frosting starts to form, would that suffice? For example if the dT was normal and then there was a big sudden change just before or during the ice forming, is it then safe to assume there is some kind of intermittent restriction somewhere?

I would say if you have same dT before and after ice forming is started, than you could exclude air flow change as possible problem.

I checked service manual and I see that you have TXV on that unit.
Check his function by heating valve bulb with your hand when icing starts. I bet on faulty TXV.

[airefresco]

Nike I don´t think so. I think there is just a capillary, are you sure you are looking at the right manual? The one Brian posted at the top is the correct one I think. If there was a TXV then I would agree with you and I would have checked that first.

[multisync]

Nike I don´t think so. I think there is just a capillary, are you sure you are looking at the right manual? The one Brian posted at the top is the correct one I think. If there was a TXV then I would agree with you and I would have checked that first.

On some of the large LG they would have a fixed orifice in the outdoor as well as a capliary on the indoor unit. I had one fail and it would frost from the outdoor unit -took out the compressor..

[airefresco]

Is that frost on the pipe? This system doesn´t do that. The frost line appears to start at the suction line leaving the evap, the liquid/expansion line doesn´t frost at all. Just the suction line. I know that does make it seem like it is a dirty coil, but i´m not convinced, the fault is too random to be that. Or I am completely wrong and going to proper stupid when it is that. :p

I don´t think it has anything like that. According to manual it´s just the capillary, which seems odd to me as the capillary is not very long. I was expecting the strainer to be something else like a fixed orifice, but again according to the manual, it´s just strainer.

[nike123]

Nike I don´t think so. I think there is just a capillary, are you sure you are looking at the right manual? The one Brian posted at the top is the correct one I think. If there was a TXV then I would agree with you and I would have checked that first.
You are right, my mistake, I presumed that is heat pump model (since we here only use heat pump models).

[nike123]

Is that frost on the pipe? This system doesn´t do that. The frost line appears to start at the suction line leaving the evap, the liquid/expansion line doesn´t frost at all. Just the suction line. I know that does make it seem like it is a dirty coil, but i´m not convinced, the fault is too random to be that. Or I am completely wrong and going to proper stupid when it is that. :p

I don´t think it has anything like that. According to manual it´s just the capillary, which seems odd to me as the capillary is not very long. I was expecting the strainer to be something else like a fixed orifice, but again according to the manual, it´s just strainer.


Jep, strainer is only that, pipe with mesh!;)
If you have frost on exit pipe from evaporator than it is probably some problem with air flow.
If you have restriction than you wil have cool/frozen liquid/evaporation pipe and much hotter exit pipe due to high superheat caused by restriction.
Next possibility is that suction line is somehow kinked/warped at connection with indoor unit or inside unit. I saw that few times.
If you inspect that and found that is noting wrong, I would change fan condenser no mater what is his reading on multimeter. Maybe he is faulty and loose its capacity from time to time. Also these fans could collect lot of dust on its blades and that could slow their rotation, but, as far as I know, they have monitoring sensor in fan motor for control of correct fan speed. How much deviation logic of microprocessor tolerate, I don't know.
If you don't have a way to measure air flow, you could measure current of fan. That will tell you if there is any difference in air flow before frost start to form and when it starts since fan current is dependent on airflow.

[Jase]

The unit is not over condensing by any chance is it?
These General/Fuji units have a tendency to do this.
What's the running pressures and temperatures of the unit?

Jase

[airefresco]

Over condensing was one of my original thoughts, but I tried it with one of the condenser fans unplugged and still iced up. The ambient is warmish here anyway.

When I´ve been there the ambient has always been around 23ºc and the room temp around 25ºc. The suction pressure drops as it starts to ice up. I managed once to get a suction pressure under normal conditions, which was 90psi, but the unit started to freeze a minute or so after getting that reading, so I don´t know how reliable that reading is. Once the unit is iced up the pressure can be anywhere between 50-70psi. The suction line temp changes all the time, so it difficult to get a reading.

[qqjersey]

After you weigh in your charge what is your pressure and your TD across coil

[airefresco]

The 90 psi reading was taken when the unit was first switched on (after everything had settled down) from weighing the gas in. The suction line iced up about 1-2 minutes after switch on. After about 5 minutes it defrosted by itself and ran fine then for 10-15 minutes before freezing again. Unfortunately I didn´t write down what the TD was, but from memory I think it was 12ºc (25ºc air on, 13 air off), taken shortly before it froze up the second time. I may take these readings again to confirm this is correct.

I don´t think I can get the fan current as I don´t think it is possible to get the cover off the electrical box while the unit is in position, but I will have a go and see.

thanks.

[frank]

Can you post a picture of the frosting pattern?

[bright]

the thing on your picture is a drier as i can ,can you please try to change it and put a new one.what are your pressures when the unit iced up ,start icing,defrosted.?i am suspecting there is a restriction within the systen especially the drier, replace it and evacuate the system.

[paul_h]

look for where the icing -up starts, that is normally a good place to check first !
Yep as said, there's only a strainer and capillary on the outdoor unit. Look for where the icing up starts.
If it's the strainer or capillary causing the problem, the 'liquid' line would be icing up first, plus all the other issues associated with it being 'short of refrigerant', ie high suction temps, higher discharge temps, water dripping from the evap etc.
If the suction temp is low and iced up etc, I wouldn't be looking at the strainer or capillary.
Maybe suction line restriction (kink, blocked evap, accumulator etc.
as wallerboy76 said, the frost will start at the restriction, you need to see where it starts

[airefresco]

Ok a few points here, in the picture that is definitely a strainer.

The ice only forms on the suction line. The liquid/expansion line does not freeze at all. It´s difficult to see where it starts because it happens so fast. It takes about a minute from the suction line sweating and everything being OK, to the full suction line and accumulator being frozen. I´ll try and film the unit icing up so you can see better what I mean.

[Makeit go Right]

Another idea: When checking airflow, the coil was judged to be okay but it is also worth checking the fan wheel(blades) of the indoor unit. Particularly in a bar, the blades can get caked up and the curved blade becomes a rod. While a curved blade would throw the air forward with umph, a 'rod'blade wuld just paddle it a bit.

Noticeable if there is not much umpf (throw, velocity) in the supply air leaving the unit outlet.