evaporator ice formation
 

Somebody mentioned several days ago that ice formation on an a
refrigeration evaporator can be caused by low freon (or perhaps air in
the system, I don't recall which). I've been wondering about that for
the past few days. Why would low freon or air in the system cause ice
formation? I'm just curious as to what the theory behind that is.

--
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Vic Dura wrote:
I'm just curious as to what the theory behind that is.

When the refrigerant charge is low the evaporator coil gets starved for
refrigerant and this results in reduced pressure at the inlet piston or
expansion valve, thus allowing the refrigerant to vaporize at a lower
temperature - below 32 degrees. At this point the first part of the
coil will freeze. Then, since ice is a fairly good insulator the
refrigerant will now travel further through the coil before encountering
an exposed surface. More ice forms and the process continues. Gradually
most or all of the evaporator coil will be covered with ice. This of
course blocks air flow through the coil.

Travis Jordan wrote:
Vic Dura wrote:

I'm just curious as to what the theory behind that is.


When the refrigerant charge is low the evaporator coil gets starved for
refrigerant and this results in reduced pressure at the inlet piston or
expansion valve, thus allowing the refrigerant to vaporize at a lower
temperature - below 32 degrees. At this point the first part of the
coil will freeze. Then, since ice is a fairly good insulator the
refrigerant will now travel further through the coil before encountering
an exposed surface. More ice forms and the process continues. Gradually
most or all of the evaporator coil will be covered with ice. This of
course blocks air flow through the coil.


What a concise, helpful answer.
Thank you.

Jim

Vic Dura writes:

Why would low freon or air in the system cause ice formation?

It does seem paradoxical, but it is true:

http://groups-beta.google.com/group/...20eda678cc180f

Richard J Kinch wrote:
It does seem paradoxical, but it is true:

http://groups-beta.google.com/group/...20eda678cc180f

But not quite for the reason stated:
" 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 "

The evaporator temperature is a result of the vaporization of the
refrigerant, not "too-low suction pressure".

On Wed, 29 Jun 2005 12:49:15 GMT, in alt.home.repair
evaporator ice formation "Travis Jordan" wrote:

Vic Dura wrote:
I'm just curious as to what the theory behind that is.

When the refrigerant charge is low the evaporator coil gets starved for
refrigerant and this results in reduced pressure at the inlet piston or
expansion valve, thus allowing the refrigerant to vaporize at a lower
temperature - below 32 degrees. At this point the first part of the
coil will freeze.

Ok, that makes perfect sense to me. Thanks for the clear explanation.

--
To reply to me directly, remove the CLUTTER from my email address.

"Vic Dura" wrote in message
...
On Wed, 29 Jun 2005 12:49:15 GMT, in alt.home.repair
evaporator ice formation "Travis Jordan" wrote:

Vic Dura wrote:
I'm just curious as to what the theory behind that is.

When the refrigerant charge is low the evaporator coil gets starved for
refrigerant and this results in reduced pressure at the inlet piston or
expansion valve, thus allowing the refrigerant to vaporize at a lower
temperature - below 32 degrees. At this point the first part of the
coil will freeze.

Ok, that makes perfect sense to me. Thanks for the clear explanation.


I think another way to look at it is when the compressed freon enters the
condenser it is a hot gas. If there is the correct amount of freon, just
the right amount of heat will be removed such that it will change to a
liquid but still be quite hot. The hot liquid expanded through the
evaporator gets the correct amount of cooling.

If the freon is low there may be only a small amount of liquid exiting the
condenser and it will be cooler than normal. When it expands in the
evaporator it can produce temperatures below freezing.

Rich256 wrote:
"Vic Dura" wrote in message
...

On Wed, 29 Jun 2005 12:49:15 GMT, in alt.home.repair
evaporator ice formation "Travis Jordan" wrote:


Vic Dura wrote:

I'm just curious as to what the theory behind that is.

When the refrigerant charge is low the evaporator coil gets starved for
refrigerant and this results in reduced pressure at the inlet piston or
expansion valve, thus allowing the refrigerant to vaporize at a lower
temperature - below 32 degrees. At this point the first part of the
coil will freeze.

Ok, that makes perfect sense to me. Thanks for the clear explanation.



I think another way to look at it is when the compressed freon enters the
condenser it is a hot gas. If there is the correct amount of freon, just
the right amount of heat will be removed such that it will change to a
liquid but still be quite hot.

If you consider 80 to 110 deg "quite hot".

The hot liquid expanded through the
evaporator gets the correct amount of cooling.

If the freon is low there may be only a small amount of liquid exiting the
condenser and it will be cooler than normal.

Not necessarily, it could be hotter than normal. It depends upon how low
the charge is.

When it expands in the
evaporator it can produce temperatures below freezing.

hvacrmedic

Travis Jordan wrote:

Richard J Kinch wrote:

It does seem paradoxical, but it is true:


http://groups-beta.google.com/group/...20eda678cc180f

But not quite for the reason stated:
" 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 "

The evaporator temperature is a result of the vaporization of the
refrigerant, not "too-low suction pressure".

It's a result of the vaporization under too-low of a suction pressure.
More to the point, it's a result of the coil's skin temperature dropping
below freezing, because of the vaporization under too low of a suction
pressure.

hvacrmedic

Travis Jordan writes:

The evaporator temperature is a result of the vaporization of the
refrigerant, not "too-low suction pressure".

No. Vaporization occurs from heat transfer, not temperature. Heat and
temperature are two different things, which most people confuse.

Look at the saturation pressure-vs-temperature tables.

Many refrigeration systems are designed for the evaporator to run below 32F,
so they have a defrost feature.

--

Christopher A. Young
Learn more about Jesus
www.lds.org
www.mormons.com


"Vic Dura" wrote in message
...
Somebody mentioned several days ago that ice formation on an a
refrigeration evaporator can be caused by low freon (or perhaps air in
the system, I don't recall which). I've been wondering about that for
the past few days. Why would low freon or air in the system cause ice
formation? I'm just curious as to what the theory behind that is.

--
To reply to me directly, remove the CLUTTER from my email address.

Richard J Kinch wrote:
No. Vaporization occurs from heat transfer, not temperature. Heat
and temperature are two different things, which most people confuse.

Look at the saturation pressure-vs-temperature tables.

You are correct - and that is what I meant to say.

"Richard J Kinch" wrote in message
. ..
Travis Jordan writes:

The evaporator temperature is a result of the vaporization of the
refrigerant, not "too-low suction pressure".

No. Vaporization occurs from heat transfer, not temperature. Heat and
temperature are two different things, which most people confuse.

Look at the saturation pressure-vs-temperature tables.

"Richard J Kinch" wrote in message
. ..
Travis Jordan writes:

The evaporator temperature is a result of the vaporization of the
refrigerant, not "too-low suction pressure".

No. Vaporization occurs from heat transfer, not temperature. Heat and
temperature are two different things, which most people confuse.

Look at the saturation pressure-vs-temperature tables.

This is Turtle.

there is a point in the Back pressure and head pressure points where at this one
point that the evaperator will freeze up on low freon. In the Louisiana area it
is on R-22 at 38 to 42 psi back pressure and other parts of the country up as
high as 50 psi back pressure. A system can freeze up on low freon but usely only
at one temp it will do it at.

TURTLE

"RP" wrote in message
...


Travis Jordan wrote:

Richard J Kinch wrote:

It does seem paradoxical, but it is true:


http://groups-beta.google.com/group/...20eda678cc180f

But not quite for the reason stated:
" 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 "

The evaporator temperature is a result of the vaporization of the
refrigerant, not "too-low suction pressure".

It's a result of the vaporization under too-low of a suction pressure.
More to the point, it's a result of the coil's skin temperature dropping below
freezing, because of the vaporization under too low of a suction pressure.

hvacrmedic


This is Turtle.

What you spoke about here has been on my mine for YEARS and ties into the
evaperator coils on hvac system up at 38 psi to 42 psi in Louisiana and other
lower humidity areas at 50 psi. Do you know any places where a fellow could read
up on this freezing of the coil at lower temp and pressures of the evaperator
coil.

TURTLE