Icing up due to overcharge?

[hsteiner]

A co-worker insists that a overcharge on a AC unit can result in iced up condition.
I always thought icing was caused by undercharge or low airflow so I disagreed with him.
Who is right?

[fat eddy]

Either one has the potential to ice up the evaporator, suction line and compressor,

[davidwtfng]

Is this an actual situation/problem? In any event, check your Delta T and head pressure, this would give a good indication of either overcharge or undercharge. Frostback can occur for both so you should turn off the system first and allow it to defrost first. To answer your question, your both right at the same time your both not.

[davidwtfng]

oh yeah, I forgot something...
Check your superheat!!!

[hsteiner]

Thanks for the answers. This is really just a theoretical question. If somebody could explain how an overcharge causes the suction to drop below the freezing point, I'd appreciate it. I have always thought a overcharge would result in high perssures, both suction and liquid line.

[drivewizard]

An overcharge alone by itself will not cause a A/C system to ice up.

[kerndt]

Hsteiner, your basic logic is correct and you are more right than your co-worker.

The A/C evaporator is more likely to ice up due to slight under charge condition. I think you understand that under charged condition will lower your boiling point of your refrigerant, thus potentially reducing the evaporator temperature below freezing, causing ice to form.

If the A/C system is slightly over charged, AND the heat load into the evaporator is low, its temperature CAN drop below freezing, and your suction line might freeze back to the compressor. Understanding that the abnormal low heat load really is what caused the icing suction line.

Hsteiner 99% correct
Co-worker 1% correct

[hsteiner]

[i]
Hsteiner 99% correct
Co-worker 1% correct
[/B]

I like that, thanks!

[airworx]

if you have a system which uses a txv what happens is when you overcharge a system the txv will close off which will
drop suction pressure and cuase icing. this is more prevelant in refrigeration but i have seen it freezeup exvs on flotronic chillers but cant remember any dx systems doing this not to say it wouldnt but could if certain conditions exist.

[kerndt]

Airworx
An over charged Txv system, will not directly cause an evaporator freeze up. At most it will result in excessive high head pressure, and reduce the compressors efficiency. If you think I’m wrong, please explain your logic.

[phosgene]

Not saying it can't happen but I have never seen a overcharged system ice up. Undercharged units, I see one iced up at least once a week.

[airworx]

if youre running a low temp box, the temperture of the coil
will drop as you flood the evap coil with refrigerant thus
the bulb of txv senses it pinches off, lowers suction pressure which lowers temps which causes the suction line to frost or freeze.

on an exv system the overcharge will be sensed by the evap being flooded with suction sensor which will keep the valve pinched off and the exv will freeze up.

[Edited by airworx on 04-03-2005 at 11:20 PM]

[kerndt]

Airworx
An overcharge condition will not directly cause your evaporator to flood with refrigerant. Excess refrigerant or excess high pressure will not effect an TXV or EXV enough to cause it to flood the evaporator. Even if you have off cycle liquid migration, the flooded condition would only be temporary, and would clear quickly after compressor starts. YES the TXV and EXV will shut down, but only until they sense a superheat condition, which will happen real fast with a heat load on the evaporator, this will not cause the coil to ice over.

As other people have replied, over charging directly does not causing a evaporator to ice up.