Freezing AC Evaporator
K2
freezes up? By freeze up I mean get completely covered in ice/frost such
that its not cooling the house. This seems to happen once or twice a
year and for the life I can't figure out any pattern that might explain
why it happens. I don't believe it's the humidity (I live in Maryland)
because it's worked fine on days that are much more humid than today.
Anyone have any possible ideas for why this is happening?
Thx
-K2
Gordon Reeder
Insufisient air flow. Could be a clogged filter, dirty coils,
Blocked return plenium. Too many rooms closed off.
--
Just my $0.02 worth. Hope it helps
Gordon Reeder
greeder
at: myself.com
TURTLE
"K2" <ad...@host.com> wrote in message
news:MPG.15f2468fb6040b7f989686@news...
This is Turtle.
It can be any number of things but here is a list to start with.
1 Low Freon Level & on certain weather conditions you get a 40 to 50 PSI
suction and it will freeze up.
2 Plugged or dirty Evaperator coil.
3 Furnace or air handler fan speed set too low or dirty blower wheel.
4 Too many discharge register cut off to the rooms in the house.
5 To Sum it up " Lack of air flow or low freon level " .
I think I would invest in a Check up on your system for this can be costing
you big bucks on your electric bill by running low on freon or having lack
of air flow for some reason.
TURTLE
Dan Hicks
Basically, this happens either because the unit is low on freon or the
airflow is sub-standard for some reason. Reasons for below-standard
airflow can be a multi-speed motor running at too low a speed, a clogged
air filter, or too many AC registers turned off.
Generally, if icing is marginal it won't occur on the most humid days
but on days of moderate humidity.
--
Dan Hicks
To live is so startling, it leaves little time for anything else.
--Emily
Dickinson
K2
> K2 wrote:
> >
> > Can anyone tell me why, occasionally the evaporator on my air conditioner
> > freezes up? By freeze up I mean get completely covered in ice/frost such
> > that its not cooling the house. This seems to happen once or twice a
> > year and for the life I can't figure out any pattern that might explain
> > why it happens. I don't believe it's the humidity (I live in Maryland)
> > because it's worked fine on days that are much more humid than today.
> > Anyone have any possible ideas for why this is happening?
>
> Basically, this happens either because the unit is low on freon or the
> airflow is sub-standard for some reason. Reasons for below-standard
> airflow can be a multi-speed motor running at too low a speed, a clogged
> air filter, or too many AC registers turned off.
>
> Generally, if icing is marginal it won't occur on the most humid days
> but on days of moderate humidity.
>
>
to help that is found in this group. Many thanks to Gordon Reeder,
TURTLE, and Dan Hicks for their help. You guys called it, the filter was
absolutely plugged. So much for my experiment with expensive, reusable
furnace filters.
Thanks Again
-K2
Dr.Hardcrab
So much for my experiment with expensive, reusable
> furnace filters.
Go to Wallmart and buy the $17.99 reusable filter. Comes in 20" X 25" with
real easy instructions on how to cut to the size you need (just a pair of
scissors will do it). I vacuum mine when it needs it (instead of hosing it
off) and it's amazing how well they cut down on the dust in the house.
Not a salesman for Wallmart, just happy with a product they carry......
mchap
Sorry, I don't agree with being low on freon. I hear people say this from
time to time but the fact is that low freon causes a warmer evaporator, not
a colder one. Anyone with a set of gauges can show you how low freon
increases gauge pressure. If this is a window unit, and most freeze ups
occur on window models, then the common reason is that the unit is
oversized for the room(s). If this is a central unit, (which doesn't seem
likely), then I would suggest that you clear the condensate drain. It may be
blowing standing water up onto the evaporator and freezing.
K2 <ad...@host.com> wrote in message news:MPG.15f2468fb6040b7f989686@news...
Tony Miklos
TURTLE wrote:
> This is Turtle.
>
> It can be any number of things but here is a list to start with.
>
> 1 Low Freon Level & on certain weather conditions you get a 40 to 50 PSI
> suction and it will freeze up.
This is something I don't understand. If low freon causes the
evaporator to freeze up, I would guess it is running colder than normal,
right? So why isn't this taken advantage of when designing a system?
If it gets colder than normal with low freon, the airflow could be
increased, and the efficiency would go up? What am I missing here? (I
understand the basics of refrigeration, but no, I never had a real
education on it.)
Just Curious,
Tony
Dan O.
Tony Miklos wrote
>
>If low freon causes the
>evaporator to freeze up, I would guess it is running colder than normal,
>right? So why isn't this taken advantage of when designing a system?
>If it gets colder than normal with low freon, the airflow could be
>increased, and the efficiency would go up? What am I missing here?
If the evaporator gets colder than needed, the condensation that forms on the
evaporator coil freezes up (as is the case in the original message) and plugs
it. Once the evaporator coil is frosted over, you would need some sort of heater
to defrost it (hence a frost free refrigerator).
Plugged evaporator coil = no air movement = no effective cooling.
As you can see, they do use that methodology for refrigeration, just not usually
for air conditioners where you only need to cool the air to 70° instead of sub
zero temperatures.
Dan O.
-
Appliance411.com
http://www.Appliance411.com/
=Ð~~~~~~
Dan O.
mchap wrote in message ...
>Hi,
>Sorry, I don't agree with being low on freon. I hear people say this from
>time to time but the fact is that low freon causes a warmer evaporator, not
>a colder one. Anyone with a set of gauges can show you how low freon
>increases gauge pressure.
If you look at a refrigerant pressure temperature chart, you will see that
temperature DECREASES with a decrease in refrigerant pressure. That's why
refrigerators run at a lower pressures (beside a different refrigerant).
You may end up seeing warmer temperatures out of the refrigeration appliance as
without enough refrigerant, less heat removal can take place. It doesn't mean it
won't get cold.
Dan O.
-
Appliance411.com
http://www.Appliance411.com/?ref411=air+conditioner
=Ð~~~~~~
Tony Miklos
"Dan O." wrote:
>
> Tony Miklos wrote
> >
> >If low freon causes the
> >evaporator to freeze up, I would guess it is running colder than normal,
> >right? So why isn't this taken advantage of when designing a system?
> >If it gets colder than normal with low freon, the airflow could be
> >increased, and the efficiency would go up? What am I missing here?
>
> If the evaporator gets colder than needed, the condensation that forms on the
> evaporator coil freezes up (as is the case in the original message) and plugs
> it.
What I am asking is why don't they decrease the freon, and increase the
fan speed to the point that the condensation doesn't freeze? I would
think it would make the unit more efficient.
--
Tony
Dan Hicks
>
> Hi,
> Sorry, I don't agree with being low on freon. I hear people say this from
> time to time but the fact is that low freon causes a warmer evaporator, not
> a colder one.
People say it all the time because it's true.
--
Dan Hicks
To love to read is to change hours of ennui for hours of delight. --
Montesquieu
CBHVAC
close to a vac, simply because pressure and temp are related when dealing
with any refrigerant. This is why we measure superheat when charging a unit.
Now..what do you mean anyone with a set of gauges can show you how low freon
increases pressure? If the suction side of the compressor is below 57.5PSI,
you have a coil temp that is below freezing....and yes...THATS on my gauges
too. Lets use R22, for example.: 57.5 PSI=32F, 43.0PSI=20F, and on the
higher end: 76.0PSI=45F, 450.0PSI=155F...how can you or anyone else see that
low refrigerant causes a higher reading?
If a unit is charged correctly, you COULD stand there with a hose on the
evap coil, and it would NEVER freeze.
The purpose of the evap coil, is twofold: one, it REMOVES heat from the air,
refrigerant being the vehicle that does this, and removes moisture from the
air via condensation on the cool surface, similar to a glass of ice sitting
out on a table on a warm day. If the refrigerant is charged correctly, and
the amount of air flowing over the coil is correct FOR that unit, then, you
WILL NOT get a freezing coil. As air volume increases, pressures will
increase slightly, and as it DEcreases, the pressures will drop.
This is one of the main reasons that when the evap coil starts to clog due
to lack of service, a hack tech will automatically add refrigerant to a
system, and not realize he is overloading the system. One of the first
things any competent tech will check, if the gauges read low pressures is
the airflow over the coil...and the coil itself. Most of the time its either
a clogged filter, or a clogged evap coil, and the unit DOES NOT need more
freon.
There does come a point, when a unit can be low on refrigerant, and the coil
will not freeze, as there is not enough refrigerant flowing in the volume of
the coil to allow this, or remove any ambient heat to amount to anything.
THEN, the unit can be low, but not freezing the coil, or cooling.
Better check your advice before you give out wrong advice....and sorry to
say, you did.
Now...about a window unit...its possible that if the condenser has excessive
condensate blowing on it, from a slinger ring on a fan, due to excessive
water standing in the pan, its possible to drop the evap coil pressures
below the freezing mark due to the condenser removing more heat from the
freon than designed.
All a slinger ring is designed to do is to help the unit operate a bit more
efficient, not to soak the condenser in water. Same principle on home split
systems...when the outside unit is serviced, and restarted, it needs to be
run long enough for all the water that is still in the coil from the
flushing of the cleaners to evaporate and be removed....otherwise, the
readings will be WAY off due to the increased cooling at that point. One
could apply the same thinking that the reason that its not wise to run a
central unit if the outside temps are below 50F...and why outdoor
thermostats are sometimes used on units in various parts of the country.
--
www.carolinabreezehvac.com
"mchap" <mcha...@planetkc.com> wrote in message
news:toibbhk...@corp.supernews.com...
Dan Hicks
It would make it less efficient. The efficiency of refrigeration
devices is pretty mysterious, even after you study the Carnot cycle in
physics class.
--
Dan Hicks
The world is full of suffering. It is also full of overcoming it.
David Murphy
Hi Dan Hicks, hope you are having a nice day
26-Aug-01 06:55:49, Dan Hicks wrote to All
Subject: Re: Freezing AC Evaporator
DH> From: Dan Hicks <danh...@ieee.org>
DH> Basically, this happens either because the unit is low on freon or
DH> the airflow is sub-standard for some reason. Reasons for
DH> below-standard airflow can be a multi-speed motor running at too low
DH> a speed, a clogged air filter, or too many AC registers turned off.
DH> Generally, if icing is marginal it won't occur on the most humid days
DH> but on days of moderate humidity.
Wrong again dan. The more humidity, the more icing will occur due to the
moisture in the air. Icing up is due to The humidity freezing onto the coil.
.. "Everybody remember where we parked". -- Adm. Kirk, STIV
___ TagDude 0.92á+[DM]
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
spam protection measure, Please remove the 33 to send e-mail
David Murphy
Hi mchap , hope you are having a nice day
25-Aug-01 23:18:11, mchap wrote to All
Subject: Re: Freezing AC Evaporator
m> From: "mchap" <mcha...@planetkc.com>
m> Hi, Sorry, I don't agree with being low on freon. I hear people say
m> this from time to time but the fact is that low freon causes a
m> warmer evaporator, not a colder one. Anyone with a set of gauges can
m> show you how low freon increases gauge pressure. If this is a
m> window unit, and most freeze ups occur on window models, then the
m> common reason is that the unit is oversized for the room(s). If this
m> is a central unit, (which doesn't seem likely), then I would suggest
m> that you clear the condensate drain. It may be blowing standing
m> water up onto the evaporator and freezing.
Sorry but you are wrong on all counts. low refrigerant will freeze a coil and
water blowing on it will not freeze if the charge is proper. where does the
water come from anyway? it comes from the evaporator condensating which
means it is dripping down and off of the evaporator also, if it was oversized
it would short cycle and would never freeze.
.. By all means, let's not confuse ourselves by the facts.
David Murphy
Hi Tony, hope you are having a nice day
26-Aug-01 04:52:38, Tony Miklos wrote to All
Subject: Re: Freezing AC Evaporator
TM> From: Tony Miklos <tmi...@netcarrier.com>
TM> What I am asking is why don't they decrease the freon, and increase
TM> the fan speed to the point that the condensation doesn't freeze?
TM> I would think it would make the unit more efficient.
As was stated in another message. you need to look at a PT chart and you will
see why it is done that way. different pressures and temps are relative and
you couldn't run at lower pressures as the evap would be too cold and would
freeze causing the need for a defrost cycle which would be rather counter
productive.
.. Thought I wouldn't notice you sneaking off, eh?
art james
>
>
> Wrong again dan. The more humidity, the more icing will occur due to the
> moisture in the air. Icing up is due to The humidity freezing onto the coil.
How dare you question Dan Hicks! Hell, he knows everything about
everything. Just ask him.
Greg O
You are wrong! Lower pressure = lower temps.
Greg
"mchap" <mcha...@planetkc.com> wrote in message
news:toibbhk...@corp.supernews.com...
David Murphy
Hi art, hope you are having a nice day
26-Aug-01 00:13:26, art james wrote to All
Subject: Re: Freezing AC Evaporator
aj> From: art james <f...@times.com>
aj> David Murphy wrote:
>> Wrong again dan. The more humidity, the more icing will occur due to
>> the moisture in the air. Icing up is due to The humidity freezing
>> onto the coil.
aj> How dare you question Dan Hicks! Hell, he knows everything about
aj> everything. Just ask him.
That's his problem, he thinks he knows everything. I have seen so many wrong
answers I just can't let it go by any more.
.. You can't have everything. Where would you put it?
Vicki
K2 wrote:
> I continue to be amazed at the vast amount of knowledge and willingness
> to help that is found in this group. Many thanks to Gordon Reeder,
> TURTLE, and Dan Hicks for their help. You guys called it, the filter was
> absolutely plugged. So much for my experiment with expensive, reusable
> furnace filters.
>
> Thanks Again
> -K2
"Expensive, reusable furnace filters" still have to be
CLEANED. I wash mine every month when I write out the
mortgage payment." They're not maintenance-free.
Dan Hicks
>
> Hi Dan Hicks, hope you are having a nice day
>
> 26-Aug-01 06:55:49, Dan Hicks wrote to All
> Subject: Re: Freezing AC Evaporator
>
> DH> From: Dan Hicks <danh...@ieee.org>
>
> DH> Basically, this happens either because the unit is low on freon or
> DH> the airflow is sub-standard for some reason. Reasons for
> DH> below-standard airflow can be a multi-speed motor running at too low
> DH> a speed, a clogged air filter, or too many AC registers turned off.
>
> DH> Generally, if icing is marginal it won't occur on the most humid days
> DH> but on days of moderate humidity.
>
> Wrong again dan. The more humidity, the more icing will occur due to the
> moisture in the air. Icing up is due to The humidity freezing onto the coil.
Yes, there is more moisture in the air. But if the dew point is real
high the AC can't lower the dew point to freezing in one pass through
and the coil won't freeze. Basic physics -- if the AC can't remove the
heat fast enough to lower the air temp to freezing then it won't freeze,
and the more moisture in the air, the more heat must be removed.
--
Dan Hicks
Generosity is giving more than you can, and pride is taking less than
you
need. --Kahlil Gibran
Dan O.
>
>>
>> Tony Miklos wrote
>> >
>> >If low freon causes the
>> >evaporator to freeze up, I would guess it is running colder than normal,
>> >right? So why isn't this taken advantage of when designing a system?
>> >If it gets colder than normal with low freon, the airflow could be
>> >increased, and the efficiency would go up? What am I missing here?
>>"Dan O." wrote:
>>
>> If the evaporator gets colder than needed, the condensation that forms on the
>> evaporator coil freezes up (as is the case in the original message) and plugs
>> it.
>
Tony Miklos wrote
>
>What I am asking is why don't they decrease the freon, and increase the
>fan speed to the point that the condensation doesn't freeze? I would
>think it would make the unit more efficient.
>
If it did I'm fairly certain they would be using it by now.
In lower temperature systems, there is also less heat transfer taking. So it
might be fine if you just wanted to cool a small area but I don't think it would
work well for a larger area.
There is also the problem that if the evaporator gets too cold, sublimation
would take place where the moisture turns directly to frost as soon as it hits
the evaporator, like in a frost free refrigerator.
There comes a point of diminishing returns. Not too many people would want the
air coming out of their air conditioner like a jet engine. Although, sometimes .
. .
Dan O.
David Murphy
Hi Dan Hicks, hope you are having a nice day
26-Aug-01 19:11:13, Dan Hicks wrote to All
Subject: Re: Freezing AC Evaporator
DH> From: Dan Hicks <danh...@ieee.org>
DH> Yes, there is more moisture in the air. But if the dew point is real
DH> high the AC can't lower the dew point to freezing in one pass
DH> through and the coil won't freeze. Basic physics -- if the AC can't
DH> remove the heat fast enough to lower the air temp to freezing
DH> then it won't freeze, and the more moisture in the air, the more
DH> heat must be removed.
Dan you really need to go back to that engineering school again. You are of
course quite wrong. I have been an A/C tech for over 25 years, and you?
.. "After they make styrofoam, what do they ship it in?" - s.w.
CBHVAC
installed is hard on a unit....if you can find ONE that is causing a
problem, either not cooling correctly, or find ONE that has caused a motor
to burn out, that WE have installed, I will buy you the system of your
choice.
There is more than one design of perm filter out there....--
www.carolinabreezehvac.com
"Sam" <ThisIsNotmy...@mail.com> wrote in message
news:Xns9109E147F1714Th...@206.13.28.182...
> K2 <ad...@host.com> wrote:
> > the filter was
> > absolutely plugged. So much for my experiment with expensive,
> reusable
> > furnace filters.
>
> the excessive air flow restriction they usually cause unless you have
> oversized return filter grilles - a rarity.
>
> --
> Sam
> Delete "ThisIsNot" to email.
Vicki
as long as I have been an HVAC&R journeyman. Even used them
in the units at a hospital where I worked for five years.
But I'm smart enough to wash them once a month.
Of course, I only live in Phoenix -- where it was 114º
today.
Sam wrote:
>
> K2 <ad...@host.com> wrote:
> > the filter was
> > absolutely plugged. So much for my experiment with expensive,
> reusable
> > furnace filters.
>
Tony Miklos
So it won't work, but there is no way to explain it to me in this
forum. Especially since I never even HEARD of the Carnot cycle. Oh
well. I figured it wouldn't work, I just wanted to know why.
--
Tony
CBHVAC
Honeywell's and The Web filters meet ASHRAE specs, and like I will state
again, will NOT cause a problem. If they are causing a problem, such as a
furnace that is tripping the high limit, then the high limit would be at
fault most of the time, adjusted wrong or otherwise...its also possible that
the fan blower is clogged, or other problem.
If the coil is icing, then superheat was not set correctly to begin with and
THATS the problem. While an electrostatic filter is a bit more restrictive,
again I state that IF the design and filter type is correct, you will NEVER
have a problem. There is more than one type of electrostatic filter on the
market, and there is NOT one magic one size fits all applications. If the
return is undersized to begin with, as in a home that was originally heat
only, and the AC contractor did not do a duct calc and left the original
duct, then yes, I can see a problem...the point being, and bottom line is
this:
I have never had a problem with the over 500 or so filters are installed per
year by us...of course, they are installed during service, and if the unit
is up to par, and clean, and fan speeds are correct, there is never a
problem after installation.
Taking your side for a moment, you are not the only one I have heard this
from, but I really think that if you are seeing that many cause problems,
you may be overlooking another problem...other than undersized duct.
In all honesty, I see the 3M cotton filters that have the copper fibers in
them to be more restrictive than a Honeywell 3 stage electrostatic...thats
what I currently run on my system, in addition to a UV lamp setup...after I
installed one here, my wife, who had been showing classic signs of hayfever
since her move to the South from the deserts of California, has been fine.
They do as advertised, provided there is no other problems...
I really think you and I are on the same path here, just going about
expressing it differently.,,,,but to say all electrostatics are junk, is
simply not correct.
--
www.carolinabreezehvac.com
"Sam" <ThisIsNotmy...@mail.com> wrote in message
news:Xns910A840696D59Th...@206.13.28.182...
> "CBHVAC" <in...@carolinabreezehvac.com> wrote:
>
> > You really like posting that dont you....come tell me where any one
> we
> > installed is hard on a unit....if you can find ONE that is causing a
> > problem, either not cooling correctly, or find ONE that has caused a
> motor
> > to burn out, that WE have installed, I will buy you the system of
> your
> > choice.
> > There is more than one design of perm filter out there....--
>
> CBHVAC, I don't recall mentioning you in my follow up. The most
> commonly sold reusable electrostatic filters are junk. They can and
> often do cause coil icing and can even cause the furnace to shut down
> on high limit.
>
> Also, I'm sure you are capable of correctly size a return filter, but
> most are undersized, as you well know. Add a restrictive air filter
> to it and you're asking for trouble.
>
> --
> Sam
Dan Hicks
Consider that Carnot cycle efficiency is basically determined by the
difference in temperature between the two heat sinks that you're pumping
heat between. You want 50 degree air, more or less, and the outside
temp is, say, 90F, giving you a difference of 40 degrees. If you make
the evaporator coil real cold, say 33F (ie, just above freezing to avoid
icing) then the difference will be 57F. Basically, pumping across a 40
degree differential will take only 40/57 of the energy of pumping across
a 57 degree differential, so it makes no sense to cool the coil to 33F
when you want 50F air. Rather, you want to cool the coil to just below
50F and move the air across slowly enough to achieve 50.
There are various ways to control the temperature of the evaporator
coil, but simplest is to "overcharge" the system slightly so that the
evaporator coil pressure never drops real low. Even if a thermostatic
expansion valve is used, the system will still be slightly "overcharged"
in this sense in order to make the valve's job easier.
--
Dan Hicks
You can't hold a man down without staying down with him.
Richard J Kinch
>If low freon causes the
>evaporator to freeze up, I would guess it is running colder than normal,
>right? So why isn't this taken advantage of when designing a system?
The failure process is simple; no need for complex principles to get a
basic understanding. However, you should appreciate that heat and
temperature are two different things. The fact that something is cold
doesn't mean that it is transferring heat.
Essentially, with a low charge, you have a greatly reduced net cooling, but
it happens to all concentrate in a small margin of the evaporator.
With a low charge, you only get a dribble of liquid into the evap, which is
at too low a temp because of the too-low suction pressure. At first only a
tiny bit of the evap freezes at the start of the line. The rest of the
evap is warm. But then the growing frost/ice coating insulates that part
of the evap from the air flow, and the frosting area grows a little further
down the line. Eventually the frost and ice cover the whole thing, but the
net heat transfer is very poor. The ice build-up both insulates the evap
and eventually plugs all the air flow.
It's a odd process indeed, but the fact that a bit of the evap is really
cold doesn't at all mean that the unit is really pumping much heat.
Tony Miklos
Thank You,
Tony