Home » Public Forums » GMCnet » Ignorant Refrigerant Question (Optimum Amount?)
| Ignorant Refrigerant Question [message #134464] |
Wed, 13 July 2011 11:53  |
A Hamilto
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Registered: April 2011
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I have read in this forum that about 3 cans of Duracool is the "correct" amount of refrigerant in the OEM GMC dash A/C system, giving about 20psi on the low side at 1500 rpms. Less can result in pressures like 15psi at the low side and evaporator temperatures so low that water freezes in the coils and obstructs airflow.
So when you get condensation freezing in your evaporator at 15psi, why not REMOVE some Duracool to raise the temperature just enough to not freeze the condensate in the evaporator. Wouldn't you be running at lower pressure, and even less power required to turn the compressor?
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| Re: Ignorant Refrigerant Question [message #134471 is a reply to message #134464] |
Wed, 13 July 2011 13:23  |
roy1
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Registered: July 2004
Location: Minden nevada
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your understanding of evap pressure is backwards 20# pressure is about 20 deg. coil temperature which can ice the coil in a damp climate. 15# pressure is around 10 degrees coil temperature and will ice the coil everyware. 25 degrees is a safer pressure as it is around 25 degrees coil temperature. 30# is around 30 degree coil tempurature. If you can get away with 20# and the coil is saturated ( you are not short on the charge) go for it but in some cases you may need a little more to complete the charge.
roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Ignorant Refrigerant Question [message #134507 is a reply to message #134482] |
Wed, 13 July 2011 19:24 |
roy1
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| ahamilto wrote on Wed, 13 July 2011 13:47 |
| roy1 wrote on Wed, 13 July 2011 13:23 |
your understanding of evap pressure is backwards 20# pressure is about 20 deg. coil temperature which can ice the coil in a damp climate. 15# pressure is around 10 degrees coil temperature and will ice the coil everyware. 25 degrees is a safer pressure as it is around 25 degrees coil temperature. 30# is around 30 degree coil tempurature. If you can get away with 20# and the coil is saturated ( you are not short on the charge) go for it but in some cases you may need a little more to complete the charge.
roy
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No. My understanding of evap pressure is what you said - lower pressure = lower temperature.
But, if the temperature gets lower with less pressure, and that trend doesn't reverse at some point, then if I don't put any Duracool in it at all, the pressure will be zero, so will it cool to absolute zero?
Since I know that can't be true, the trend has to reverse at some pressure/charge. I am asking why isn't it possible to get to the point where the temperature starts going back up with lower pressure and then lower it just enough more that the evap temp is high enough that it doesn't ice up? Seems like that would be an extremely low pressure and the compressor would turn a lot easier.
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You lost me there all I can tell you is if you charge it up and the suction pressure is too low (1) you will be short on the charge there won't be enough refrigerant vapor in the coil for it to function properly (2) the coil will ice up a little at a time and the air will stop coming out of the vent. But yes the load on the compressor will be less it just won't cool.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Ignorant Refrigerant Question [message #134510 is a reply to message #134507] |
Wed, 13 July 2011 20:19 |
A Hamilto
Messages: 4508
Registered: April 2011
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| roy1 wrote on Wed, 13 July 2011 19:24 |
| ahamilto wrote on Wed, 13 July 2011 13:47 |
| roy1 wrote on Wed, 13 July 2011 13:23 |
your understanding of evap pressure is backwards 20# pressure is about 20 deg. coil temperature which can ice the coil in a damp climate. 15# pressure is around 10 degrees coil temperature and will ice the coil everyware. 25 degrees is a safer pressure as it is around 25 degrees coil temperature. 30# is around 30 degree coil tempurature. If you can get away with 20# and the coil is saturated ( you are not short on the charge) go for it but in some cases you may need a little more to complete the charge.
roy
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No. My understanding of evap pressure is what you said - lower pressure = lower temperature.
But, if the temperature gets lower with less pressure, and that trend doesn't reverse at some point, then if I don't put any Duracool in it at all, the pressure will be zero, so will it cool to absolute zero?
Since I know that can't be true, the trend has to reverse at some pressure/charge. I am asking why isn't it possible to get to the point where the temperature starts going back up with lower pressure and then lower it just enough more that the evap temp is high enough that it doesn't ice up? Seems like that would be an extremely low pressure and the compressor would turn a lot easier.
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You lost me there all I can tell you is if you charge it up and the suction pressure is too low (1) you will be short on the charge there won't be enough refrigerant vapor in the coil for it to function properly (2) the coil will ice up a little at a time and the air will stop coming out of the vent. But yes the load on the compressor will be less it just won't cool.
Roy
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Isn't there a point of low charge when the coil WON'T ice up? Say the charge is so low that it does not cool at all. Add a milligram at a time. Is there a point when the charge increases by a single milligram, it goes from not being cold at all to instantly being so cold that the condensation freezes?
Don't get too wrapped up in this, I just wonder why a slightly undercharged system gets colder than one that is "correctly" charged. It seems that if the evaporator starts freezing condensation, then you should lower the amount of refrigerant to just the point where the condensation doesn't freeze anymore. Seems counterintuitive to me that you add more, thereby increasing the load on the compressor.
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| Re: [GMCnet] Ignorant Refrigerant Question [message #134519 is a reply to message #134510] |
Wed, 13 July 2011 21:10 |
James Hupy
Messages: 6806
Registered: May 2010
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The correct answer is" Inversely proportional to the square of the pressure
differential". If the moisture in the ambient air freezes on the evaporator,
then no air can pass through and the efficiency of the AC is uninportant. At
20# low side pressure, no freeze up will normally occur, there is a 40 to 50
degree temp difference between ambient and internal, and everyone is happy.
If you add more duracool, the evap temp will freeze the moisture. Emery is
right. Shoot for 20psi at 1500 rpm, blower fan on high.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Wed, Jul 13, 2011 at 6:19 PM, A. <markbb1@netzero.com> wrote:
>
>
> roy1 wrote on Wed, 13 July 2011 19:24
> > ahamilto wrote on Wed, 13 July 2011 13:47
> > > roy1 wrote on Wed, 13 July 2011 13:23
> > > > your understanding of evap pressure is backwards 20# pressure is
> about 20 deg. coil temperature which can ice the coil in a damp climate. 15#
> pressure is around 10 degrees coil temperature and will ice the coil
> everyware. 25 degrees is a safer pressure as it is around 25 degrees coil
> temperature. 30# is around 30 degree coil tempurature. If you can get away
> with 20# and the coil is saturated ( you are not short on the charge) go for
> it but in some cases you may need a little more to complete the charge.
> > > > roy
> > > No. My understanding of evap pressure is what you said - lower
> pressure = lower temperature.
> > > But, if the temperature gets lower with less pressure, and that trend
> doesn't reverse at some point, then if I don't put any Duracool in it at
> all, the pressure will be zero, so will it cool to absolute zero?
> > > Since I know that can't be true, the trend has to reverse at some
> pressure/charge. I am asking why isn't it possible to get to the point
> where the temperature starts going back up with lower pressure and then
> lower it just enough more that the evap temp is high enough that it doesn't
> ice up? Seems like that would be an extremely low pressure and the
> compressor would turn a lot easier.
> >
> >
> > You lost me there all I can tell you is if you charge it up and the
> suction pressure is too low (1) you will be short on the charge there won't
> be enough refrigerant vapor in the coil for it to function properly (2) the
> coil will ice up a little at a time and the air will stop coming out of the
> vent. But yes the load on the compressor will be less it just won't cool.
> >
> > Roy
> Isn't there a point of low charge when the coil WON'T ice up? Say the
> charge is so low that it does not cool at all. Add a milligram at a time.
> Is there a point when the charge increases by a single milligram, it goes
> from not being cold at all to instantly being so cold that the condensation
> freezes?
> Don't get too wrapped up in this, I just wonder why a slightly undercharged
> system gets colder than one that is "correctly" charged. It seems that if
> the evaporator starts freezing condensation, then you should lower the
> amount of refrigerant to just the point where the condensation doesn't
> freeze anymore. Seems counterintuitive to me that you add more, thereby
> increasing the load on the compressor.
> --
> '73 23' CanyonLands
> _______________________________________________
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| Re: [GMCnet] Ignorant Refrigerant Question [message #134527 is a reply to message #134519] |
Wed, 13 July 2011 21:34 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
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[is happy.
If you add more duracool, the evap temp will freeze the moisture. Emery is
right. Shoot for 20psi at 1500 rpm, blower fan on high.
Jim Hupy
Salem, OR
78 GMC Royale #
>
> ]
Jim you guys are making my head hurt. Surely you mean if you add more Duracool it will increase the evap temperature. It will be less likely to freeze at 23# then 20#. There is also a point when the expansion valve will pinch down and the pressure won't change too much when a little more is added.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Ignorant Refrigerant Question [message #134531 is a reply to message #134527] |
Wed, 13 July 2011 21:49 |
James Hupy
Messages: 6806
Registered: May 2010
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Roy, try not to overthink it. It is not black magic. The system works by
boiling the refrigerant and then condensing it back to a liquid. Both times
it changes state, it either absorbs heat or sheds it. It absorbs heat from
the air inside the AC fan housing, and sheds it at the airstream through the
radiator. Different refrigerants posess different vapor/liquid qualities.
Duracool works most efficiently at the pressure/temperature combination that
Emery describes. Trust him, he is spot on.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Wed, Jul 13, 2011 at 7:34 PM, <roy@gmcnet.org> wrote:
>
>
> [is happy.
> If you add more duracool, the evap temp will freeze the moisture. Emery is
> right. Shoot for 20psi at 1500 rpm, blower fan on high.
> Jim Hupy
> Salem, OR
> 78 GMC Royale #
> >
> > ]
> Jim you guys are making my head hurt. Surely you mean if you add more
> Duracool it will increase the evap temperature. It will be less likely to
> freeze at 23# then 20#. There is also a point when the expansion valve will
> pinch down and the pressure won't change too much when a little more is
> added.
> Roy
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| Re: [GMCnet] Ignorant Refrigerant Question [message #134534 is a reply to message #134531] |
Wed, 13 July 2011 22:07 |
roy1
Messages: 2126
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Location: Minden nevada
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[quote title=James Hupy wrote on Wed, 13 July 2011 19:49]Roy, try
not to overthink it. It is not black magic.
Jim I was a Commercial A/C service mechanic for 40 years I have a pretty good idea how it works.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Ignorant Refrigerant Question [message #134538 is a reply to message #134534] |
Wed, 13 July 2011 22:42 |
James Hupy
Messages: 6806
Registered: May 2010
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Good. Are you a member of GMCWS? If you are, are you interested in doing a
tech presentation at Fall rally in Oct? I am looking for Tech presenters for
then. Any person who is going to attend that might be interested in being a
presenter, contact me please, so I can fill in some blanks spaces in the
tech program.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Wed, Jul 13, 2011 at 8:07 PM, <roy@gmcnet.org> wrote:
>
>
> [quote title=James Hupy wrote on Wed, 13 July 2011 19:49]Roy, try
> not to overthink it. It is not black magic.
>
> Jim I was a Commercial A/C service mechanic for 40 years I have a pretty
> good idea how it works.
> Roy
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| Re: [GMCnet] Ignorant Refrigerant Question [message #134556 is a reply to message #134519] |
Thu, 14 July 2011 08:21 |
emerystora
Messages: 4442
Registered: January 2004
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On Jul 13, 2011, at 8:10 PM, James Hupy wrote:
> The correct answer is" Inversely proportional to the square of the pressure
> differential". If the moisture in the ambient air freezes on the evaporator,
> then no air can pass through and the efficiency of the AC is uninportant. At
> 20# low side pressure, no freeze up will normally occur, there is a 40 to 50
> degree temp difference between ambient and internal, and everyone is happy.
> If you add more duracool, the evap temp will freeze the moisture. Emery is
> right. Shoot for 20psi at 1500 rpm, blower fan on high.
> Jim Hupy
> Salem, OR
> 78 GMC Royale 403
>
That is almost correct. However, in most systems, if you add more Duracool it will get warmer. If you have less Duracool such as 15 psi then it will get colder and in high humidity areas you may freeze the condensation on the fins and block the airflow.
Please note that the 20 psi is when the ambient air temperature is in the 70 to perhaps 85 degree area. If you are running on a really hot day then the pressure measured may be higher than 20 psi.
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: [GMCnet] Ignorant Refrigerant Question [message #134615 is a reply to message #134556] |
Thu, 14 July 2011 15:41 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
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[Emery I agree on this statement I had wondered if you were dead set on 20 lbs suction on a super hot day . Sometimes it's a little bit of a challenge to get it on the money unless you start from scratch with the known correct charge.
Roy
Please note that the 20 psi is when the ambient air temperature is in the 70 to perhaps 85 degree area. If you are running on a really hot day then the pressure measured may be higher than 20 psi.
Emery Stora
77 Kingsley
Santa Fe, NM
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[/quote]
Roy Keen
Minden,NV
76 X Glenbrook
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