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Maybe of minor interest, I came across this in my Insight shop manual. The liquid to the expansion valve is heat-exchanged against the vapor from the evaporator. This “tube-in-a-tube” is between (6) and (7) in the first drawing:

Knowing why it works…helps diagnose ,when it doesn’t.

I tell my kids this reasoning as we’re disassembling the broken ( insert name here ; toy, vacuum, nintendo, bucycle ) whatever to see if…if maybe we could fix it. If not then, we’ve at least we learned how it should have worked …when it worked. …why if got broken…and what we could have done different to avoid breakdown.

That is a neat idea. The cool vapor leaving the evaporator serves no purpose in the efficiency of the system. Therefore cooling the liquid refrigerant before the expansion device saves having to use liquid refrigerant for that purpose inside the evaporator.

I have no idea how this is supposed to work but I’m glad that there are other people who do. I have zero (0) interest in this subject since there is a great AC shop just down the street.

"Maybe of minor interest, …"

Make that zero interest.
  • the diagrams are too small to be legible,
  • what does “The liquid to the expansion valve is heat-exchanged against the vapor from the evaporator” mean?
  • “This tube-in-a-tube, is between (6) and (7)” ???
Very poor explanation, if you ask me.

Try clicking on the photo on the left, then hold your mouse pointer over the picture and click once more to expand.

THere must be no 8 year olds around to show you. They seem to know it all about computers, and we know about wrenches.


HE is nothing new. U compress gas, it gets hot. If u can lower the temp of hot gas/hi press tube, u achieve greater efficiency when gas is allowed to expand/drop temp. The design of HE details is adjusted based on systems capabilities and expected operating conditions. Very common in fridge use. Not so much in auto use. The issue is routing the in/out piping to cross, which increases complexity. The underhood environment is a nasty place.

I like that as it does not appear to have any negative consequences. Unlike the newer window A/C units for your house that maintain a condensate water reservoir and use the cooling fan to sling that water up onto the coils. Great idea except it just increased the annoyance level to people trying to sleep with this thing nearby sloshing water incessantly…central A/C is a blessing…

“Make that zero interest.”

Thanks, Mechaniker, for your honesty. I actually thought your response would be the more common one. The Insight also has a sunlight sensor under the windshield. When the sun shines on it, you can feel the air get colder from the vents.

I have always been a strong advocate of understanding how things work. Much to my children’s chagrin.
Cavell, I like the way you’re thinking, but allow me to suggest that a better place to start the explanation is by saying that if you compress matter it releases heat energy and if you decompress matter it absorbs heat energy. That brings the explanation beyond air conditioning into the world at large.

I’ve seen AC systems with the capillary tube strapped or soldered to the evaporator return line.
Same purpose: cools the liquid refrigerant to the evaporator.

The window units I’ve bought recently have a cap on the condensate drain that can be removed and a hose attached; no more sloshing.
I prefer to save energy over central air, cooling one floor or one room at a time.

My old house was contemporary log construction and we used window A/C. I had just bought 3 new units a year before moving. They were the latest and greatest, proclaimed to be the quietest units on the market. They were…until the condensate filled up the pan. It had a drain too but it was after an inch of water filled the reservoir! What a disappointment. I drilled a hole in one that was in my kid’s bedroom to make it drain off completely. Didn’t seem to have any noticeable effect on it.

It’s nice to be able to selectively cool on a room by room basis. Until you have to install 6 or 7 units every spring and remove them every fall. Then at least one window in every room is blocked off by the A/C unit. Plus storing them all through winter. 3 new units was close to $1000. Everybody has a different set of conditions but all those units running on 120VAC is nowhere near as efficient as one central unit running on 230VAC and a single furnace blower.

My current set up is 3 FA systems with 5 zones. In spring I flip a few switches from heat to cooling…sweet.

I just have 2 units: one for the first floor, one for the bedroom upstairs.
I’m in a 100 year old house with the big cast iron radiators, which I love.
I’ll leave it to my successors install duct work.

I have a 74 year old house, with an ultra high efficiency gas furnace and forced hot air, but I only use A/C two or three days a year. I just don’t care for A/C as a personal choice. I don’t use it in my car either. I have three window A/C units, and that does the job when necessary.