Either one has the potential to ice up the evaporator, suction line and compressor,
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?
Either one has the potential to ice up the evaporator, suction line and compressor,
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.
oh yeah, I forgot something...
Check your superheat!!!
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.
An overcharge alone by itself will not cause a A/C system to ice up.
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
I like that, thanks![i]
Hsteiner 99% correct
Co-worker 1% correct
[/B]
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.
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.
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.
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]
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.
I would agree that an overcharge would raise suction pressure and SST. I do not believe an overcharge will cause icing up like you will see with an undercharge.
Low airflow is another story but that is nothing to do with the charge.
you dont know refrigeration or txv operation then. because an overcharge will put more liquid in evap which causes a lower line temp which will close the txv off which will lower the pressure which will lower the temp which will cause frosting. if you dont belive then the next time you work on a 35 degree box overcharge to 30 or 40 degree subcooling and watch.
I don't think you know which way is up.
I never meant any disrespect.
Look at all the other posts on this thread.
I don't believe anyone agrees with you. Call sporlan tech support, at the factory, maybe they can inlighten you.
Many times a improperly operating TXV, mismatch or other restriction can lend itself to being overcharged in an attempt to get the pressures up by a less than thourough technician... So, yes an overcharged system can freeze but the root cause is the restriction.
im sorry you dont understand the refrigerant system.
If you are freezing a coil on a direct expansion air conditioning system, the more likely culprit is a lack of air flow.
When there is not enough volume (cfm) across the evaporator coil there is not enough heat to boil off the refrigerant fully and add superheat to the vapor so the refrigerant temp drops. Normally we have about 40-45 degree F. refrigerant temperature in an air conditioning coil.
There are other conditions that can cause icing of the evap coil, such as the condensing temperature being too low. This can happen for example if we are running a condensing unit with no low ambient controls with an outside air temp say 40 F. Our condensing temperature instead of being 100 F drops to 50 or so. After this 50 degree refrigerant goes through the metering device, our refrigerant temperature in our evaporator is suddenly below the freezing point of water >32 F.
So if you are freezing a dx airside coil, it is probably not from an overcharge of refrigerant.
Regards
Coolairman
The TXV allows refrigerant into the evaporator by sensing the temp of the succion line(superheat),with high superheat the temp. of the sensing buld icreases and so does its opening pressure,In a externally equalized txv the opening pressure inside the bulb fights the closing pressure of the succion line (equalizer) and the pressure of the spring.
A high subcooling (Overcharge,low ambient temp.) will not iced up the evaporator coil.
correct me if I'm wrong!