Icing up due to overcharge?

[hsteiner]

Wow, this has become a really long and interesting thread. Thanks for all the input, hopefully everybody learned a little something new, I know I did.
Just to clarify something John Dalton said: You are NOT right because although an undercharged or low airflow system can cause the unit to ice up, there are many other conditions that will generate the same symptoms as well.
I am aware of that, but the first and probably easiest things to check when checking a iced up unit are filters, fan amps, pressures and subcooling.
The point was made pretty clear throughout this thread that an overcharge on a otherwise normally operating unit will not cause icing to build, which is really what started this discussion, so I think I am a lot more right than my co-worker who apparently removed refrigerant and therby got the unit running properly.
Unfortunately this happened to him a few years back and there is no way of verifying anything.
thanks again

[john dalton]

Dear Hsteiner,

“Just to clarify something John Dalton said: You are NOT right because although an undercharged or low airflow system can cause the unit to ice up, there are many other conditions that will generate the same symptoms as well.
I am aware of that,…..”

Being aware of it, and stating it are apparently two different things, as evident in your original post my friend.


“…but the first and probably easiest things to check when checking a iced up unit are filters, fan amps, pressures and subcooling.”

When you find an iced up system, the first thing to do is shut off the compressor to deice the system, then as the system is deicing you check your evaporative motor assembly to verify it’s working and working correctly, then you can check anything mechanical in nature(filter, grills, registers, and the such). Only after the complete deice of the system can you start the system back up and obtain a complete set of operational readings to first and foremost check airflow, and then everything else.


”The point was made pretty clear throughout this thread that an overcharge on a otherwise normally operating unit will not cause icing to build, which is really what started this discussion, so I think I am a lot more right than my co-worker….”

Being a little wrong or a lot wrong is like being pregnant, after all the discussion, either you are or you’re not, period.

Thanks for the great post to get this thread started, I too believe everyone who participated here learned something new, or at least had their basic diagnostic and refrigeration skills reinforced.

Respectfully Submitted,
John J. Dalton

[hsteiner]

"My Friend" John Dalton, You sound like you need to lighten up a little, don't take things so seriously and you will get a lot more out of life, ok? bye

[rdhussmann]

If the system is overcharged it can flood back to the compressor. If an additional problem exists, like a dirty filter or a bad fan motor, the saturated evaporator temperature could be below the frost poing of the air. I would make sure everything else is clean and working properly before I let charge out of the system. Check superheat and subcooling.

High head pressure would also be a symptom of an overcharged system. A lot of systems will not pump down into the condenser or receiver, without extremely high head pressure, if they are overcharged.

[Poodle Head Mikey]

hsteiner,

I wouldn't say "impossible" but it seems damned unlikely doesn't it?

How could it happen?

A TXV will control superheat while the overchage would tend to raise head pressure and then suction presure. None of which would tend toward freezing a coil.

A cap tube would overfeed refrigerant as head pressure and Delta P increased with the overcharge. Suction pressure would rise, superheat would fall. None of which would tend toward freezing a coil.

Get you co-worker to explain in exact detail how it can happen. And then come back here and tell me.

[john dalton]

Dear Hsteiner,

Regarding your previous post:

Exactly what area do I need to lighten up on? Could it be in the area where I pointed out where you were also incorrect in your stated facts? Or possibility in the area where you were trying to justify where you were “more right than your colleague” , please let me know.

As for being too serious in my stated posts, I would agree with you that I take my profession very, very seriously. You see, I feed my family, I provide a roof over the head of my family, and I cloth my family by my profession, and I take that responsibility very seriously.

The purpose of this thread, and this forum, is to share and spread HVAC knowledge and experiences with our fellow colleagues, and that again is a serious subject. Humor on the other hand is an essential part of this forum, it lets most of us here use it when we either make a fool of ourselves on a post, find out we are wrong in an assumption or fact that we thought we knew, or when we’re trying to lighten the air when a particular thread gets a bit too heated, maybe such as a time as now.

But we don’t use humor to make fun of other colleagues, or try to hide behind it when we don’t want to admit we were wrong, there’s not a single individual here on this thread that has posted, for any length of time, that hasn’t either made a mistake, misquoted, misunderstood, or misdirected a fellow colleague down that proverbial garden path.

Just my own humble option………………….

Respectfully Submitted,
John J. Dalton

PS: As for getting a lot out of life, I have a wife of 23 years, and six beautiful children, trust me when I say, God has spared no expense in providing me more than what I deserve in the “life department”. But thank you for caring in this regard.

[john dalton]

Dear Poodle Head Mikey,

Regarding your post:

“wouldn't say "impossible" but it seems damned unlikely doesn't it?

How could it happen?”

I always tell the guys in the service department at my company; “Nothing is impossible, just highly unlikely.”

I would agree with your statement as a corrected revision to my statement, not impossible, just highly unlikely with no published operating conditions to justify a statement to the fact. In other words, give me an example of a normal air conditioning operating system with no other operating deficiencies that would cause an ice up with overcharge as a sole source of the problem, and I would state corrected.

And as stated previously, icing up of a system can be a symptom of one of several different or combination of different problems within the system.

Respectfully Submitted,
John J. Dalton

PS: Interesting handle you have, care to elaborate, blond, long, shaggy hair, ????????

[rdhussmann]

There is not enough information on many of these posts for anybody to really be right or wrong.

Any technician could be overlooking the most obvious mechanical or electrical condition, because he is so obsessed with the more complicated and theoretical questions.

[Poodle Head Mikey]

rdhussmann,

Be that as it may - he asked if overcharging will cause a evaporator to freeze.

And the answer is: No.

All the rest is just speculation and hell; half the time I can't get my own thoughts in order. So I don;t want to even attempt doing his. <g>

[rdhussmann]

Maybe he should try a different set of gauges? I know that a faulty manifold gauge or a bad gasket has had me scratching my head a time or 2.

[Poodle Head Mikey]

But that ain't what he asked. <g>

Sure: evaporator coils freeze. And although I am willing to learn how overcharging can cause that, at this point I can't make out how it could happen with overcharging as the cause. <g>

Lots of things I don't know, even in this business, but I think I've got the basic refrigeration cycle, and the components that create it, down pretty good. <g>

Poodle Head Mikey is a great Biker-grade nickname that seems like it should have a really great Story to go along with it. The kind that no one ever gets tired of hearing and time after time someone will say: "Yo Mikey! Come tell Vito how you got the Poodle Head handle! Wait 'til you hear This shit Vito! You won;t F-ing believe it! Tell him Mikey."

But there's not. <g>

Poodle Head Mikey was a cameo character role on NYPD Blue. Some boyhood pal of Ricky Schroder's character. Well when the little woman and I first heard the name spoken we were so convulsed with laughing that she fell off the bed.

A while later while I was screaming and punching the computer monitor after having tried: stephen1, stephen2, stephen3, stephentenmillionandsix, etc. my little Angel came in and soothingly said: You need a screen name that no one else on the planet would chose.

Yeah? No kidding! Like what?

And then she whispered, as only she can: How about Poodle Head Mikey?

And so it has been ever since. <g>

[rdhussmann]

TXV's are supposed to control superheat, but they don't do a good job when there is an overcharge, dirt, or broken fans. I see TXV's flooding compressors all of the time.

A lot of times it is due to an inexperienced technician who just believes that TXV's control so good, that he opens the valve to lower the superheat setting and that wasn't every the problem in the first place.

[bochen744]

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.

[airworx]

like i said my post never said airconditioning, it said refrigeration. get it or can you guys not read. read it again and again. ok read it again my reply was refrigeration not a/c.

[Poodle Head Mikey]

Airworx,

You wrote:

"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."
--------------

As far as i know, this is not how TXV's work, even in refrigeration. A TXV would have no way of 'knowing' that an overcharge existed. It only reacts to suction pressure, spring pressure, and sensing bulb pressure.

Correct me if I am mistaken, but it seems to me that, in the event of an overcharged system condition, a TXV would go right on maintaining suction superheat by controlling the flow of refrigerant through itself. It would not "close off" any more than it would under normal conditions.

Any charge in excess of subcooling minimums would accumulate (back up) in the condenser. This acumulated liquid refrigerant reduces available change-of-state heat exchage aurface area which raises the head pressure.

If this increase in head pressure had Any efect on suction pressure - it would be to raise it due to decreasing compressor efficiency.

But I do not see how any of that could result in either a lowering of suction pressure OR an evaporator freezing more than it's normal operating conditions would dictate.

Please explain to me the

sie0-
As the jhead pressure coil s the charge was


This it "could if certain conditions exist."

What specific conditions would cause this?

Thanks!

[rdhussmann]

Overcharge can cause an evaporator to flood.

Excessive pressure (r22) drop in the suction line could cause that flooded refrigerant to fall below freezing before it reaches the dome of the compressor. In fact the whole compressor could look like a ball of ice.

The thing we have to remember is that there are a lot of systems that are burning up, dying, and acting real funny, because of improper installation. There are a hundred scenarios where it could appear that an overcharged system is causing ice on the compressor, but more than likely the system was mistakenly overcharged because of poor performance that was really due to poor istallation techniques.

This guy probably solved an icing problem in the past by letting out some charge. From that day on he mistakenly thought that reducing charge is the answer to fixing an iced up compressor.

Wierd things can and do happen all of the time.

[Wild Leg]

Originally posted by rdhussmann
...Wierd things can and do happen all of the time.

That's what keeps it interesting.

[westcoast refer man]

[QUOTE]Originally posted by airworx
[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.

airworx, I see where you're going with this, but let me explain. When the head pressure rises, the capacity of the TXV increases due the the increased pressure differential across the TXV. Yes the TXV is likely to close off some because of this. If it didn't, it would likely feed too much.

However, because the capacity of the TXV increased, the same flow thru the valve can be achieved thru a smaller TXV port opening. So, the evap pressure won't rise.

Contributing to this non rising evap pressure is also the fact that as head pressure rises, the re-expansion of suction vapor upon termination of the compression stroke increases. This tends to increase saturated suction pressure.

The way I see it, the suction pressure has to go up. If so, how could a higher saturated temperature lead to freezing?

[john dalton]

Dear Westcoast refer man,

A simple questions deserves a simple answer my friend……it can’t!

Respectfully Submitted,
John J. Dalton

[westcoast refer man]

Dear John,

A simple answer to this question hasn't cleared up the controversy. Also, a simple answer may not lead to any greater understanding of how things really work.