AC scenario
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From: Austin Texas
AC scenario
Its 105 deg today and lucky me, my AC is working.
But, after the evaporator, on the low side line going back to the accumulator and compressor, the lines are very cold.
I am wondering, does it increase efficiency significantly, if I were to insulate those lines to keep the system from absorbing heat along those lines ?
And also, as any physical chemistry student knows, compression of a gas above its inversion temperature causes it to increase in temperature - does it also benefit if we can put cooling fins along the high side lines ? Indeed, the condensor is theoretically where the heat is to be dissipated, but has anyone ever put fins on the high side lines ?
What would be good is a heat exchanger between the low pressure side after the evaporator that absorbs some of the heat from the high side line after it exits the condensor. Then, I bet my R134-A would blow maybe almost cold as R-12
But, after the evaporator, on the low side line going back to the accumulator and compressor, the lines are very cold.
I am wondering, does it increase efficiency significantly, if I were to insulate those lines to keep the system from absorbing heat along those lines ?
And also, as any physical chemistry student knows, compression of a gas above its inversion temperature causes it to increase in temperature - does it also benefit if we can put cooling fins along the high side lines ? Indeed, the condensor is theoretically where the heat is to be dissipated, but has anyone ever put fins on the high side lines ?
What would be good is a heat exchanger between the low pressure side after the evaporator that absorbs some of the heat from the high side line after it exits the condensor. Then, I bet my R134-A would blow maybe almost cold as R-12
Le Mans Master
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From: Orlando FL
That’s an interesting concept.
But I believe the evaporator temperature is limited or governed by the boiling point temperature of R134 (vs R12) at a given pressure at the expansion valve. I don’t think a cooler liquid line back to the expansion valve will make a lower boiling point into the evaporator.
I just know that more will add to this with more information.
But I believe the evaporator temperature is limited or governed by the boiling point temperature of R134 (vs R12) at a given pressure at the expansion valve. I don’t think a cooler liquid line back to the expansion valve will make a lower boiling point into the evaporator.
I just know that more will add to this with more information.
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From: Austin Texas
Ultimately the systems' ability to provide cool air to the cabin depends on how well the system can dissipate heat to the external surroundings.
When heat is permitted to enter the system, say, for example by the cold low pressure side's lines absorbing heat, the cooling efficiency is reduced.
So, I took some of that pipe insulation and covered up the low side line everywhere I could under the hood.
It was kind of dumb to have the cold, low pressure side line routed in the path of where the heat from the condensor blows. I swear I can feel a difference now but it might be my imagination since I did not measure any numbers. But in principle it should be cooler and that agrees with what I think I'm observing. At any rate, it can't hurt to prevent heat from entering the system by insulating the low pressure side line between the evaporator and compressor.
When heat is permitted to enter the system, say, for example by the cold low pressure side's lines absorbing heat, the cooling efficiency is reduced.
So, I took some of that pipe insulation and covered up the low side line everywhere I could under the hood.
It was kind of dumb to have the cold, low pressure side line routed in the path of where the heat from the condensor blows. I swear I can feel a difference now but it might be my imagination since I did not measure any numbers. But in principle it should be cooler and that agrees with what I think I'm observing. At any rate, it can't hurt to prevent heat from entering the system by insulating the low pressure side line between the evaporator and compressor.
Le Mans Master
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From: Orlando FL
Not sure where to agree or disagree with your logic. The Freon in the cold line (that you are insulating) from the evaporator to the accumulator to the compressor has already left the evaporator and done its job. Hopefully all the liquid from the expansion valve as boiled off and vaporized completely in the evaporator.
When it exits the evaporator it should be all gas and starts to warm up on its way to the compressor. By keeping those lines insolated as you indicated, why would it help the evaporator temperature.
When it exits the compressor as a high pressure gas, the temperature is very high.
When it exits the evaporator it should be all gas and starts to warm up on its way to the compressor. By keeping those lines insolated as you indicated, why would it help the evaporator temperature.
When it exits the compressor as a high pressure gas, the temperature is very high.
Last edited by pcolt94; Jun 26, 2012 at 09:51 PM.
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From: Austin Texas
Le Mans Master
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From: Orlando FL
I am not going to say that you are wrong in theory. That's why lines in a home unit are insulated but those lines are much longer and more susceptible for heat loss and absorption.
However in the car the lines are short and I don’t know if a real benefit would be achieved with the insulted lines. I know it would be a cost for the car companies, but you would think they would insulate them if there was a appreciable gain.
Having said all that stuff now, my 280ZX Datson has the cold line wrapped. There probably is a technical reason to wrap the pipe but I guess we'll have for wait for the answer from SunCr.
If the gas entering the compressor is cooler, then the compressed gas out might me cooler also. But how would this help? The condenser is trying to get the gas down to a liquid so I could see it from that point of view.
However in the car the lines are short and I don’t know if a real benefit would be achieved with the insulted lines. I know it would be a cost for the car companies, but you would think they would insulate them if there was a appreciable gain.
Having said all that stuff now, my 280ZX Datson has the cold line wrapped. There probably is a technical reason to wrap the pipe but I guess we'll have for wait for the answer from SunCr.
If the gas entering the compressor is cooler, then the compressed gas out might me cooler also. But how would this help? The condenser is trying to get the gas down to a liquid so I could see it from that point of view.
Last edited by pcolt94; Jun 27, 2012 at 01:05 PM.
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From: Austin Texas
*** Me too, would need to meaasure gas temp as it exits evap, and compare to the compressor inlet temp.
*** Since the gas is always above its inversion temperature, upon phase change, compression, there will be a release of enthalpy andcondensor dissipation is the only effective remover of heat , reabsorbtion of heat dissipated by condensor into the compressor inlet is counterproductive to cooling. Guess that's the easiest way I can think to say it. Works for me, I had extra pipe insul laying around, cost me nuthin and I think its cooler.
Melting Slicks
Joined: Aug 2008
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From: Palmdale CA
Chris, I've seen these lines wrapped on some vehicles, and not on others. Must be a Decision a Thermal engineer/management made based on Data receaved during a test. Recently I had my House HVAC "HERS" tested, and the technician informed me of the emportance of wrapping the low side between the "A" coil and Compressor. I was missing a couple feet of wrap next to the outside unit...
Anyhow, it would have been cool if you had taken a data point or two before wrapping..
Anyhow, it would have been cool if you had taken a data point or two before wrapping..
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From: Austin Texas
I only used the home-depot style stuff you use on home water heater hot line, polyurethane pre-bored, it comes off pretty easy. My trouble is I don't have infrared thermometer or other way to measure the temps. I have two heat pumps at the house and those lines are insulated too.
What's the air temp under the hood on a 100 degree day ? I'd guess hotter in some places than others but where that low pressure return line runs, its probably about 195. There's only a barely perceivable difference between the condenser inlet and outlet, by hand touch (caution) and I'm amazed at the cooling we get in the first place.
Most of the cooling for the condensor comes from those fans and they're limited obviously. A bigger condensor might be a nice thing to have.
Melting Slicks
Joined: Sep 2008
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From: Cherokee National Forest TN
Suggest leaving the AC lines as is, labor intensive, minimal results.
You will get colder 134 air at low vehicle speed by increasing air flow through the condenser.
If both radiator fans do not run when the AC is on tie the fan ground wires together @ the relays so they do. Adding an aftermarket cooling fan in front of the condenser will also help.
You will get colder 134 air at low vehicle speed by increasing air flow through the condenser.
If both radiator fans do not run when the AC is on tie the fan ground wires together @ the relays so they do. Adding an aftermarket cooling fan in front of the condenser will also help.
Le Mans Master
Joined: Jan 2006
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From: Orlando FL
Is not too late !
I only used the home-depot style stuff you use on home water heater hot line, polyurethane pre-bored, it comes off pretty easy. My trouble is I don't have infrared thermometer or other way to measure the temps. I have two heat pumps at the house and those lines are insulated too.
What's the air temp under the hood on a 100 degree day ? I'd guess hotter in some places than others but where that low pressure return line runs, its probably about 195. There's only a barely perceivable difference between the condenser inlet and outlet, by hand touch (caution) and I'm amazed at the cooling we get in the first place.
Most of the cooling for the condensor comes from those fans and they're limited obviously. A bigger condensor might be a nice thing to have.
I only used the home-depot style stuff you use on home water heater hot line, polyurethane pre-bored, it comes off pretty easy. My trouble is I don't have infrared thermometer or other way to measure the temps. I have two heat pumps at the house and those lines are insulated too.
What's the air temp under the hood on a 100 degree day ? I'd guess hotter in some places than others but where that low pressure return line runs, its probably about 195. There's only a barely perceivable difference between the condenser inlet and outlet, by hand touch (caution) and I'm amazed at the cooling we get in the first place.
Most of the cooling for the condensor comes from those fans and they're limited obviously. A bigger condensor might be a nice thing to have.
I think you can get a rough idea if the difference is enough to measure. But you would really need same conditions for the best (accurate) results. Engine temperature, ambient temperature of air, same speed and sun intensity would all need to be pretty close to really be fair.
Suggest leaving the AC lines as is, labor intensive, minimal results.
You will get colder 134 air at low vehicle speed by increasing air flow through the condenser.
If both radiator fans do not run when the AC is on tie the fan ground wires together @ the relays so they do. Adding an aftermarket cooling fan in front of the condenser will also help.
You will get colder 134 air at low vehicle speed by increasing air flow through the condenser.
If both radiator fans do not run when the AC is on tie the fan ground wires together @ the relays so they do. Adding an aftermarket cooling fan in front of the condenser will also help.
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From: Austin Texas
Just route the line between the evaporator exit and compressor inlet... through the throttle body where the stock setup passes coolant through.
If running radiator coolant through the throttle body when its cold outside is enough to help the engine perform better, then cooling the throttle body ought help performance by cooling the intake air charge.
lol, I'm way out on a limb now.
If running radiator coolant through the throttle body when its cold outside is enough to help the engine perform better, then cooling the throttle body ought help performance by cooling the intake air charge.
lol, I'm way out on a limb now.
Le Mans Master
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From: San Diego, Ca
For the most part, ambient will determine temp (and I don't know of any way to change that), but potentially, a possible way to start slugging liquid at the compressor. When the refrigerant has completely boiled, it gains sensible heat and becomes a superheated gas and a superheated gas has to give up that heat before it can return to a liquid. Create a pressure drop - by insulating the suction line, kaboom goes the compressor, particularly if its overcharged (which happens all too frequently in the DIY world). Mobile ac has never adopted this tech - and probably for good reason - they want it to stay together until the warranty is gone. Your home a/c is a different story as is the subcooling that happens in the Condenser.
Last edited by SunCr; Jun 27, 2012 at 09:15 PM.
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From: Austin Texas
For house, yeah.
http://www.checkthishouse.com/11/ref...nsulation.html
Why should a car's system behave differently ? Weaker compressors ?
How does insulating the low pressure line cause a pressure drop ? Does it cause similar pressure drop when ambient is 20 degrees less ?
If insulating is bad, then there must be some factory spec for how much heat the suction side is supposed to absorb from underhood, but that
would perhaps sound a bit ludicrous.
http://www.checkthishouse.com/11/ref...nsulation.html
Why should a car's system behave differently ? Weaker compressors ?
How does insulating the low pressure line cause a pressure drop ? Does it cause similar pressure drop when ambient is 20 degrees less ?
If insulating is bad, then there must be some factory spec for how much heat the suction side is supposed to absorb from underhood, but that
would perhaps sound a bit ludicrous.
Last edited by ChrisWhewell; Jun 27, 2012 at 09:42 PM.
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From: Austin Texas
These guys were kicking this stuff around, I tend to agree with "punisher" about halfway down the discussion
http://www.bobistheoilguy.com/forums...Number=1757656
http://www.bobistheoilguy.com/forums...Number=1757656
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
I note there's a post about liquid and what it does to the compressor so someone else has probably locked one up - probably by cramming too much into it.
These things leave the Factory with a five minute suck and fill and the only test is a computer scan of the Pressure Sensor. The Accumulator cleans up the quickie by the Manufacturer, but relying on it to constantly deal with liquid or complete liquid? I just don't feel that lucky, even doing it myself. If you are going to do it, I'd get superheat before and after at the Evaporator outlet and Compressor Head (though after may be too late if the charge was questionable to begin with). If you want to gain 1 or 2 degrees on a 100 degree day, remove an oz or two - assuming you have the equipment - or go to a shop, let them suck it all out and put in a balanced charge, and then, with a thermometer in the Center Vent, add and subtract until it gets the lowest temp.
I like the forum here a lot better: www.ackits.com as the guys actually do mobile a/c for a living and though it's been awhile since I hung out there, this topic comes up from time to time.
These things leave the Factory with a five minute suck and fill and the only test is a computer scan of the Pressure Sensor. The Accumulator cleans up the quickie by the Manufacturer, but relying on it to constantly deal with liquid or complete liquid? I just don't feel that lucky, even doing it myself. If you are going to do it, I'd get superheat before and after at the Evaporator outlet and Compressor Head (though after may be too late if the charge was questionable to begin with). If you want to gain 1 or 2 degrees on a 100 degree day, remove an oz or two - assuming you have the equipment - or go to a shop, let them suck it all out and put in a balanced charge, and then, with a thermometer in the Center Vent, add and subtract until it gets the lowest temp.
I like the forum here a lot better: www.ackits.com as the guys actually do mobile a/c for a living and though it's been awhile since I hung out there, this topic comes up from time to time.
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From: Austin Texas
Where I'm at from reading all the stuff I've seen on this aging topic, is that insulating the low side line probably increases efficiency somewhat, but the potential corrosion of the lines outweighs the gain in efficiency from the auto mfr. standpoint so they didn't do the expense of adding it.
I ran mine with insulation a couple days now in 105 deg weather and its been nice and cold. I'll run it this summer then look for visual signs of corrosion in October when the avg. daily temps here drop into the 80's.
I ran mine with insulation a couple days now in 105 deg weather and its been nice and cold. I'll run it this summer then look for visual signs of corrosion in October when the avg. daily temps here drop into the 80's.