[georgelass]

I'm at odds with another tech and he's a stubborn relative.

One of says a low-charge can cause a frozen
evap coil. The other one of us says the only way
a low-charge can "cause" a frozen evap coil is if the homeowner
is so frustrated with the poor cooling that he/she leaves the
a/c on all night when outdoor ambient (and ultimately indoor ambient)
temperatures drop beyond what a normal person would use a/c
with. This person also believes that between a low-charged unit
and a proper charged unit, the proper charged unit would
ice over sooner in such conditions because it would be
better at dropping the temp of the return air to very cold.

This person believes that under normal ambient conditions and with proper airflow,
a low-charged system canNOT ice over. Who is wrong?

(Uh, this is residential A/C, not a heat pump, not refrigeration.)

Thank you.

 

[Redwood650]

I suppose it all depends on the Saturation temperature of the evaporator no? If its too low, the gas will absorb too much heat (SH) and wont allow the coil/lineset to freeze... The only time I have seen a frozen coil is from low/no airflow...

 

[Tony3696]

Ask them both if the "Flux Capacitor" was checked. Whoever answers incorrectly get's kicked in the squash and sent back to school. Better yet, hook up an old A/C and try it both ways. The answer is 42.

 

[catmanacman]

Low charge can a frozen coil once the saturated temp drops below 32 degrees the system can freeze sometimes it will somtimes it wont depends on the conditions

 

[Pete954]

I thought this was basic but I guess it's different everywhere. Here in So Fla this is fairly common. So much so that my mentor taught me that all frozen evaps boil down to either low/no airflow or low refrigerent charge. Let it thaw completely, check your pressures and break out the leak detector. Unless of course it's a dirty coil or bad indoor fan, or bad cap, or restricted return, or.......you get the idea. Good luck, hope you were on the right side of the debate.

 

[newoldtech]

I've run so many calls for frozen coils and the cause was low refrigerant that I stopped counting many years ago. Low refrigerant equals low pressure equals low temperature equals ice. Could air flow issues be contributing? Sure you need to check the coil and air flow, but usually adding the proper amount of refrigerant makes the Icing magically go away.

 

[martyinlincoln]

A unit can have suction saturation temp above 32 degrees and be low on charge. Once it gets below that,to a point, then it will start to freeze any condensation on the evap coil. Keep on going until the charge is low enough that the metering device is fed gas instead of liquid and it won't freeze. You both lose the bet.

 

[VanIsleRefrig]

Low refrigerant equals low pressure equals low temperature equals ice.

Bazinga

 

[drife678]

31 degrees will freeze lol

 

[pecker head]

I've run so many calls for frozen coils and the cause was low refrigerant that I stopped counting many years ago. Low refrigerant equals low pressure equals low temperature equals ice. Could air flow issues be contributing? Sure you need to check the coil and air flow, but usually adding the proper amount of refrigerant makes the Icing magically go away.

I second that... I have been on many many calls for a iced up evap coil due to low pressures...

 

[kamersoutdoor]

Only if conditions are right will coil freeze (low return temps). Otherwise high superheat as result of starving evap.
If i have an iced coil in 80 deg dwelling I am not looking for low charge. I am tackling overcharge, or low airflow.
Last guy I worked for assumed every frozen coil was a low charge situation. He was wrong 100% of the time. I told him that you cannot apply that scenerio to every job cause you caught it once!!!
Maybe this is why i find so many overcharged systems

Sent from my SAMSUNG-SGH-I717 using Tapatalk 2

 

[kamersoutdoor]

I second that... I have been on many many calls for a iced up evap coil due to low pressures...

You add refrigerant on low pressure alone?
How about checking airflow?

Sent from my SAMSUNG-SGH-I717 using Tapatalk 2

 

[KnewYork]

A unit can have suction saturation temp above 32 degrees and be low on charge. Once it gets below that,to a point, then it will start to freeze any condensation on the evap coil. Keep on going until the charge is low enough that the metering device is fed gas instead of liquid and it won't freeze. You both lose the bet.

You made another assumption that wasn't part of the OP question. I've seen compressors almost completely cased in ice with the coils in the same condition...cause: low refrigerant charge. Your assumption is that the refrigerant will eventually leak to the point of no liquid feed which I agree with, but before it gets to that point you are going to have a below freezing evaporator which will freeze the condensate. Once that gets started the airflow gets compromised and the freezing accelerates.

 

[pecker head]

You add refrigerant on low pressure alone?
How about checking airflow?

Sent from my SAMSUNG-SGH-I717 using Tapatalk 2

No I would not add gas on low pressure without checking airflow first.. Dude I am past my first day of working service..

However I will repeat my first post " I second that... I have been on many many calls for a iced up evap coil due to low pressures..."

True Story...

 

[georgelass]

A unit can have suction saturation temp above 32 degrees and be low on charge. Once it gets below that,to a point, then it will start to freeze any condensation on the evap coil. Keep on going until the charge is low enough that the metering device is fed gas instead of liquid and it won't freeze. You both lose the bet.

Is the saturation temp and the line temp/temps of the coil (as opposed to the
line temp of the suction line) the same or pretty close? I've encountered
very undercharged units, those with saturation temps below 20 F, and icing
wasn't a problem. That is, I could charge the unit immediately, not have
to wait for a thaw before supply/return temps indicated normal airflow. Of
course, I can't say I was aware of the run times for those units.

I would be interested in how the temp along the coil does vary, whether it
is in fact near the saturation temp or whether it rises somewhat linearly
towards the suction line (past the coil) temp. Maybe taking temps
along the path of the coil in the condenser would give some insight into
how saturation temp and coil line temps differ. Obviously it is
easier to get temps at the condenser. Anybody ever try that?

 

[mark beiser]

When the system is low of refrigerant, to the point that the saturated temperature is below freezing, icing can/will occur in the portion of the coil where refrigerant is changing state.
Depending on the load, and other factors, it may not progress much beyond that, but usually the frost line will progress until the coil is entirely iced over, and can progress to the point that the compressor ends up with a thick coating of ice.

Anyone who claims otherwise doesn't have much field experience, and/or a good understanding of the refrigerant cycle.

 

[jkv]

Those other tech. are looking at the small picture, I had this problem low ambient temps block it up get the temps and pressure good check your charge make shur your fan speed is on high, air flow good and if all is good and it still freezing up put a low ambient fan control on it problem done.

 

[kamersoutdoor]

When the system is low of refrigerant, to the point that the saturated temperature is below freezing, icing can/will occur in the portion of the coil where refrigerant is changing state.
Depending on the load, and other factors, it may not progress much beyond that, but usually the frost line will progress until the coil is entirely iced over, and can progress to the point that the compressor ends up with a thick coating of ice.

Anyone who claims otherwise doesn't have much field experience, and/or a good understanding of the refrigerant cycle.

Textbook
Yes, iced coil can be caused by improperly low charged system. Whats this, maybe 2% of real life scenerios? (coil icing as dwelling reaches set point)
98% of "real life time", When a tech arrives at the scene it will be due to low air flow/overcharge.
Again, we're speaking real life over textbook scenerio.
I am relating to air conditioning over refrigeration in regards to op's original question


sent from my Samsung Galaxy Note

 

[bigtime]

It freezes bit by bit. The first section of the coil has saturated liquid and gas below freezing temps. After the liquid is gone it starts warming up. After it runs a while this first section with sat liq gets iced over, has no airflow due to the ice, and very little heat transfer. The liquid in the coil makes it a little farther, and the next section starts freezing. And on and on...

If the system can still keep up and cycle, maybe the coil will defrost enough in the off cycle to keep from totally freezing.

If someone said "my coil is frozen" and I got a prize for guessing right, I would guess low charge.

 

[kamersoutdoor]

It freezes bit by bit. The first section of the coil has saturated liquid and gas below freezing temps. After the liquid is gone it starts warming up. After it runs a while this first section with sat liq gets iced over, has no airflow due to the ice, and very little heat transfer. The liquid in the coil makes it a little farther, and the next section starts freezing. And on and on...

If the system can still keep up and cycle, maybe the coil will defrost enough in the off cycle to keep from totally freezing.

If someone said "my coil is frozen" and I got a prize for guessing right, I would guess low charge.

Really!
I would guess dirty filter. And 90% of the time I would win the prize,
Next guess would be that last tech on sight seen frozen coil, added gas and left without checking filter
:banghead:
Then I simply change filter, let blower defrost coil, and pull the 2 lbs of excess refrigerant dumped in by mis-guided tech (who probably read this thread and now thinks all frozen coils are undercharged systems),
Collect check and say goodbye to my newly acquired loyal customer
sent from my Samsung Galaxy Note