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Discussion Starter #1
Hi All,
I have a mod for the A/C system to take some of the load off the
compressor. With the A/C on we take a pretty good hit on the mpg’s.
This is fairly simple and straight forward with logical results. I further
insulated the low-pressure pipe (cold pipe) that goes from the compressor
to the firewall. It’s the thicker of the two pipes and has a “L” on the
charging access cap. Before starting I cleaned the area with windex.
This is one of the mods where my first attempt bombed. I had insulated
it with a sticky back dense insulation tape which did not work very well.
Oh well, yanked it back off.
Home Depo has a split hose insulation with sticky back that does work.
It’s called Armacell, comes in 6’ lengths and is only a few bucks each.
If you wish to do this mod you’ll need two lengths ( one Fits ½” Cop. And
one Fits ¾” Cop. ). They also have a flat light foam 2” wide sticky back
tape. You’ll need a roll of this for securing the seams of the Armacell.
As you’ll note Honda did think to insulate part of the pipe with a short
piece ( aprox 12” ) of foam where the pipe is the highest and probly the
hottest. It’s held in place by a few small spots of glue. The hardest part of
the pipe to do is between this foam and the firewall ( no room ). By twisting
and turning the foam Honda put on you can break the glue loose and walk
the foam down the pipe till it’s up against the firewall. That takes care of the
most difficult part of the pipe. You can use the ½” foam to do the rest of the
aluminum pipe and the ¾” foam to do the rubber hose part ( as far down
towards the compressor as you can reach ). Near the highest part of the pipe
you’ll find a black/white clip that snaps on to the high and low-pressure pipes,
this can be removed. Just forward of this clip there’s a metal clamp with a
8mm bolt (10mm hex head ) that secures the low-pressure pipe. This can be
removed. Just forward of this is a length of black spiral plastic rapped
around the rubber part of the hose, this can be removed as well. After
insulating the pipe I cut the spiral plastic into 3 equal pieces and rapped it
around the insulated pipe where the metal clamp was. Put a tie-rap through
the hole where the bolt was and around the insulated pipe to secure it.
I used the flat sticky back foam tape to seal the tubing ends and seams.
Although it may not be necessary I put the car on blocks, removed the engine
under panels along with the aluminum panel they attach to at the front to
do the rest of the cold pipe. Did use clear tape to help sticky back set.
Results are what you’d expect. The hot engine compartment is sucking
less cold out of the low-pressure pipe so the compressor doesn’t have to
work as hard. This equates to better mpg’s. At highway speeds you’ll
feel small surges as the compressor cycles more ( those pesky marketing
people probly didn’t like this ) but it results in being able to maintain
better speed. Lean burn works better too.
Here in Venice FL it gets pretty hot in summer, 90+. Time to complete
mod: ½ hour shopping, 1 hour staring at engine compartment and about
1 hour to apply and secure insulation. Happy cooling…
Hope I did these pics right..When you get to the pics click on
"normal size" for a better view ( I hope ).

http://community.webshots.com/user/jackmpg
Jack
P.S. Checked and the pics seem ok. Thanks for the consideration,
patience and assistance of all who helped in this enlightened group.
Window tint also good, throwing dish towel over steering wheel to
protect it from sun. Also, Canvas Works in Sunnyvale, CA makes
one of those folding/rollup winshield reflectors for the Insight,
model # 799. A similar mod could be done to the HCH.
 

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What a great idea! I have to put that on the to do list. I like the fact that it will add almost no weight to the car. :D
 

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Unlike the CRX the bolts go straight down. :D

I used spacers made of flat machinable PVC plate. I used a hole saw to create the round disk and then drilled the center hole larger to match the M8 and M10 bolts. I only raised the front .4 inch and the back .25 inch. Sounds like nothing but it feels quite different. I might go farther in the future but I would need to get longer metric bolts. The threads are 1.25 pitch. I will try to get SS cap head machine screws from Fastenall. You will notice that the seat belt is fastened to the seat so that is why they used larger bolts on the back and used an anti vibration glue on them. They are quite stiff to remove innitially. If I find a source for longer bolts I'll let you know.
 

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I did the AC mod today! before I installed the insulation I checked to see just how cold the bare aluminum tubing got. Man was it cold to touch!

I installed 4.5 feet of black closed cell - three quarter inch rubber insulation by slitting it open and then sealing it up using aluminum tape. I picked up the insulated tube from an air conditioning supply house for 12 dollars CDN. The insulated tube had "Aerocel-EPDM / UV resistant" marked on the side. It was big enough to fit over the rubber hose and fittings. The aluminum tape was from Venture Tape, Rockland, MA 02370-0384, USA. I had picked it up at a hardware store a few years back. It works where other tapes fail and has dozens of uses around the shop. Thanks to Jackmpg for the heads up on this mod! :D
 

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I hate to burst everyone's "bubble" in this thread but the modification will have _no_ impact on MPG _and_ has the potential for AC compressor damage.

The large line returning from the evaporator is called the suction line. Refrigerant vapor is being drawn from the evaporator directly into the compressor. Any "cold" not exchanged by the evaporator is lost (actually its heat absorbed). To think of it another way; since this pipe is outside the cabin its ability to help cool the cabin is nada.

The compressor must not be "fed" liquid refrigerant under any circumstances. Should the volume of incoming liquid exceed the volume of the compression chamber in the compressor "slugging" occurs. Liquid is not very compressible and something will have to give.

The lack of insulation on this return pipe helps assure (yes its a minimal factor) that any remaining liquid in the return line can fully evaporate and expand into a gas.

Insulate the return line to the compressor? Don't do it!
 

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Hi, sorry for my lack of knowledge on this but are you sure that in the line, the cold side is liquid. I always tought that is was gas on both sides: one side compressed and hot. the other with less compression therefore colder, but not liquid.
 

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Yves M. said:
Hi, sorry for my lack of knowledge on this but are you sure that in the line, the cold side is liquid. I always tought that is was gas on both sides: one side compressed and hot. the other with less compression therefore colder, but not liquid.
The "cold" side is not liquid, its evaporating liquid (gas).

Hint: You wrote it yourself "one side compressed" what is a compressed gas?

Link:

http://home.howstuffworks.com/ac2.htm

The link doesn't have a flow direction arrow, read the narrative which describes a clockwise flow on this diagram.

HTH! :)
 

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Thanks for the link! I finally learned how a "Propane Refrigerator" works, been asking myself this for more than 20 years but never took time to find out. Good site.

I see your point on the liquid. But I would not expect it to be possible. Since the cold comes from evaporation (pressure diff at the expansion valve), the fact that the tube is cold should prove that the cold side is gas, like you wrote near the compressor
 

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OK, so I've doe the mod, my AC hasn't failed yet but you have put some questions into my mind.

I ask myself:

The manual says to operate the air conditioning occasionally in the winter. So what happens then? Part of the pipe was already insulated by Honda, was this a mistake?. A cold object absorbs heat which in an air conditioning system must be eliminated by using energy, so doesn't this energy have to come from the motor? What happens if you run the AC on max but the fan on low, or the reverse?

It's late, brain tired, round is good. :)
 

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Operation for a few minutes once a week insures that all internal seals etc. get their dose of lubricating oil.

"Insulation" of low side pipes is usually done to prevent condensation and the resulting water drip. I haven't looked at the area myself to give my best guess as to why.

you wrote:

"A cold object absorbs heat which in an air conditioning system must be eliminated by using energy, so doesn't this energy have to come from the motor?"

I'm trying to understand the question here or even a statement but I'm missing it somewhere. Perhaps your explanation of quote "It's late, brain tired..." says it all.

The energy input which allows the refrigerant to absorb heat comes from the compressor (and ultimately the ICE in our case). By compressing a well chosen gas, cooling it into a liquid (in the condenser), then evaporating it you can "move" heat. BTW the most efficient refrigerant is ammonia. Its used in large refrigerant units but its also toxic and wouldn't be well suited to an automotive application. Read: a fender bender in which the condenser gets punctured could easily turn into a fatal accident!



Refrigerant flow in a Honda system is regulated by the expansion valve. It can increase or restrict the refrigerant flow within a narrow window. R-12 (Freon) boils @ -25F, R-134 (Suva) as I recall boils at a slightly higher temperature. If you don't regulate the amount of refrigerant flowing through the system the evaporator could easily reach the boiling temperature. Any moisture in the air would freeze solid on the evaporator eventually causing complete air flow blockage.

The overall systems volume, the designed operating temperature range, range of the expansion valve and amount of refrigerant charge must be balanced to assure correct operation.

Insulating the low pressure side plumbing outside the cabin of any automotive AC system has no impact on its operational efficiency. And depending on many design factors it is theoretically possible this insulation will prevent the refrigerant from fully evaporating causing the compressor to intake liquid refrigerant. A compressor subjected to this situation will not last long. The most likely conditions for this scenario will be AC on in cold weather or a "stuck open" expansion valve (which is one mode of failure for this part). In our Insights and in most other cars AC on is automatic with defroster on.

Are you dooming your compressor to fail with this mod? Nope! But some of the design margin of safety is being used that would prevent this type of damage. That's all this mod is accomplishing.

HTH! :)
 

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Recently talked to the tech at my local dealer (he's been through all the Honda training on hybrids.) When I told him about this mod he also stated that it would have no affect on the cooling properties of the AC. He did not mention anything about damaging the vehicle however.

The insulation currently on the L line is there for vibrations and keeping condensation away from electrical lines (not so much a problem in the Insight but he mentioned another car had that problem.)
 

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Discussion Starter #14
Oops, maby not

Hi All,
Yep, like anyone I’ve made boo-boos before. But before you start removing the insulation from your AC low-pressure pipe lets go into a little more detail on how AC works. Yes, John is right, liquid refrigerant induced into the compressor would be fatal, for the compressor that is. Since we have to start somewhere let’s start at the heart of the AC system, the compressor, and work our way around to the infamous low-pressure pipe… The compressor does what it’s name implies, it takes cool refrigerant gas from the low pressure pipe, compresses it into a hot gas and sends it on to the condenser (radiator looking thing in front of the engine). The condenser cools the hot gas to a liquid after which it goes thru the receiver/dryer, which removes moisture and debris from the refrigerant. This cooled liquid then goes thru the expansion valve. This valve has a controlled orifice (for temp. control). The refrigerant is sprayed (like a garden hose nozzle) into the inlet side of the evaporator, which causes the refrigerant to change state to a gas and become colder (lower pressure). The evaporator is like another radiator where the cold gas passing thru removes heat from the car cabin. This cooled gas then travels thru the low-pressure pipe to the compressor where the process begins again. If the refrigerant left the evaporator as a liquid the compressor might be in deep sxxt. But it doesn’t, not part of the process. For that to happen would require catastrophic failure of the expansion valve. Insulation or no insulation, if this were to occur the compressor may have only moments to live, kinda like when the chicken tried to cross the street…The insulation will only enhance the efficiency (yes, I'll do the high pressure pipe too, products like armacell are designed for this, not just sweating, hot or cold pipes). Should I Armacell the high-pressure pipe? Let’s see if I can blow the hood off this sucker.
Related URL’s:http://www.coolcar.co.nz/view_link.php?id=1
http://www.natmus.dk/cons/tp/aircon/aircon1.html
http://www.acdoctor.com/air_conditioning/air_conditioning.htm
There’s a man standing alone in a remote forest. His wife is nowhere to be seen. He utters a single word. Is he still wrong? I could be too…just not this time
 

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Ok, I've scanned the links. The last on in your list also links to a second page for tips in how to improve cost savings.
I didn't see any tip involving insulation of pipes.

Insulation of the high pressure pipe will only _reduce_ cooling performance in that you limit its ability to radiate heat from the compression process. Yes, the vast majority of heat release is accomplished in the condenser (opposite of heat absorbed in the evaporator), so insulation of this pipe will be a minimal efficiency loss.


I wrote in my earlier replies:

"The lack of insulation on this return pipe helps assure (yes its a
minimal factor) that any remaining liquid in the return line can fully
evaporate and expand into a gas."

and further explained in my last post:

"Are you dooming your compressor to fail with this mod? Nope! But some
of the design margin of safety is being used that would prevent this
type of damage. That's all this mod is accomplishing."

Yes, the damage potential is remote. But so is performance improvement.


Agreed it is counter intuitive in that the more "cold" you keep enclosed in the system the better it should perform. AFAIK it simply doesn't work that way.

I've been trying to remember the technical specifics of efficiency calculations in regard to the choice of refrigerant used. Which should help shed some light on the physics of the heat transfer process and why the temperature at the compressor intake being a few degrees cooler would only have a _minute_ effect on efficiency. (since not as much heat was absorbed not as much would need to be radiated at the condenser) But I can't find my reference book, sorry.

There have been some very physics savvy posters in here in the past. Maybe one will pass by at some point and straighten both of us out. <g>

HTH! :)
 

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Jack, my insulation is still on there.:)
 
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