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moondawn
29-05-2009, 06:22 PM
Hi guys

was at a job today where a third of the evaporater coil was iced up. it was a crafft package ac unit (window rattler)
there was too much heat in the room and this unit is struggling and is undersized.

My question is can some explain why the top of the evap iced up and what caused this.

i understand that the compressor will be permantly on as temp in the room will never be maintained but would like to know why it ices up as it did or why it ices up!

thanks in advance
moondawn
Yuri B.
29-05-2009, 06:44 PM
Most probably, it has overworked, overheated, and now just beginning to lose its refrigerant charge. Soon it will be dead if competent urgent measures are not undertaken. Now it is necessary to switch it off.
rude
30-05-2009, 07:04 PM
Filters, airflow and gas charge. Check all them and determine the problem. Also air flow on and off values.
Karl Hofmann
30-05-2009, 10:34 PM
Add to that the high humidity of the UK for the realatively low temperature.... Had an LG that used to do that but it was easily fixed with a sledge hammer:eek:

No, Really... When I replaced it FOC (My fault for selecting the wrong unit) and replaced it with a Sanyo (I only ever visit that unit for regular servicing) I placed the LG on my drive and beat the daylights out of it:eek: Saying " You wont be doing that to me again" in a very Basil Fawlty way.... My neghbours are used to my little ways now
moondawn
31-05-2009, 05:35 PM
hi all

thanks for the replies

the unit once defrosted, checked the system and it seemed to work well just could not cope with the demand. i just wondered why the icing would start cos its undersized. a walkthrough of how that process happens with a unit over working?


cheers
moondawn
Yuri B.
31-05-2009, 05:47 PM
Were filters clogged or clean when you found the ice ?
Yuri B.
31-05-2009, 06:50 PM
Your heavy struggling unit works with very large supeheat, compressor not cooled, heat gathers, head temp rise and rise.
HFC's molecules which are much less than earlier refrigerants's are bit by bit leaving the overheated system through the pores in copper pipes and loaded connections (even not speaking about the flair connections).
Evap icing up happens most offen at morning hours (if unit was left working). Outside air temp drops, pressures drop, at some moment evap pressure reaches such a low level (due to the lack of *****), that not only evap's coil - the return pipe may cover in ice. The process is aggreviated if, by that, the filter has been neglected.
If you do not measure suction pressure and superheat now soon you will lose your rattler.
Yuri B.
31-05-2009, 06:55 PM
Due not to the lack but shortage of *****, of course.
moondawn
31-05-2009, 10:39 PM
Were filters clogged or clean when you found the ice ?
Filters were spotless mate.
the unit had been serviced recently and the engineer who serviced it noticed they had added more equipment into the COMMS ROOM.

Because of this the window rattler is overworking.

i aint sure that the unit is leaking refigerant more that it is undersized and therefor working every day every second of the day which odviously is not good.

cheers
moondawn
Gary
31-05-2009, 10:56 PM
Excessive load would tend to prevent the coil from frosting, not cause it to frost.

Insufficient airflow would tend to frost the coil evenly.

Insufficient charge would tend to frost the coil from the top down.
Gary
31-05-2009, 11:00 PM
i aint sure that the unit is leaking refigerant more that it is undersized and therefor working every day every second of the day which odviously is not good.



Actually, stopping and starting is harder on a system than running continuously.
moondawn
01-06-2009, 07:06 PM
Excessive load would tend to prevent the coil from frosting, not cause it to frost.

Insufficient airflow would tend to frost the coil evenly.

Insufficient charge would tend to frost the coil from the top down.

hi gary thanks for your input

ok so its sounding as if this unit does not have enough refrigerant.

the top third of the coil was iced solid.

i could not understand why the unit iced up so glad i asked the question thanks guys
Gary
01-06-2009, 07:15 PM
ok so its sounding as if this unit does not have enough refrigerant.


It would be more accurate to say that it doesn't have enough refrigerant in the low side of the system.

This could mean that the unit is undercharged... but it could also mean that the unit has a partial restriction, not allowing sufficient liquid to flow from the high side to the low side.
exxu
01-06-2009, 07:56 PM
Check the filter drier in the liquid line if it has one.
moondawn
02-06-2009, 12:12 AM
It would be more accurate to say that it doesn't have enough refrigerant in the low side of the system.

This could mean that the unit is undercharged... but it could also mean that the unit has a partial restriction, not allowing sufficient liquid to flow from the high side to the low side.

yes very true gary as the icing is appaearing in the low side so after the expansion device it could have a problem.

thanks for all your help and the others too.

moondawn
lowcool
02-06-2009, 02:36 AM
is it 134a refrigerant per chance
Magoo
02-06-2009, 03:06 AM
Short of gas
moondawn
03-06-2009, 10:29 PM
is it 134a refrigerant per chance

hi there the gas is r407c
lowcool
04-06-2009, 03:12 AM
hi there the gas is r407c
probably rules out capillary restriction,your left with gas shortage,system restriction or slight compressor inefficiency,time to fit the gauges and do your job.
moondawn
04-06-2009, 06:09 PM
not been back to site since.

will update if i go back

thanks all
Victor537Boston
06-06-2009, 06:48 AM
Filters, airflow and gas charge. Check all them and determine the problem. Also air flow on and off values.

I agree you need to know what the pressures are most importantly as well as superheat and subcooling. Sounds to me low on gas, or the valves on the compressor are on the way so the compression ratio is not at its prime anymore.