Help me put together an A/C system...

[BioHazard]

I've put a lot of thought into powering my air conditioners with a generator, I'm starting to think maybe I should build a portable/backup direct engine powered air conditioner. I'm thinking basically a small car A/C system, and maybe an air cooled diesel....in a portable package with some flexible ducts that could be used to cool a house, a tent, or anything else...

Unfortunately I don't know a lot about air conditioning systems. I know the basics - compressor fills the condensor with refrigerant and gets hot, while the evaporator gets cold. What I don't really understand is how to size different peices of the system together?

For example, I'll start with an automotive A/C compressor. What is the smallest engine I could use to turn one, and how many BTUs can I expect? If I peice together my own condensor/evaporators, how do I know what size they should be? Does anybody know of any website or anything with a complete diagram of an automotive A/C system, so I know exactly what parts to look for? Kind of an "air conditioning for dummies"?

[mobile_bob]

i don't know where you are from, but if you have any old wrecking yards the place to start is find
and old car like an old ford and removed the  whole system. everything is there and it all is made to work together.

i once removed a complete system, without losing a drop of refrigerant, so it is possible.

failing that, look around for an aftermarket A/C installation outfit, they sell kits as well as parts.
like the old AIR underdash add on aftermarket a/c units that were fairly common.

alternatively find an old dodge motorhome that is about to be scrapped, they also have relatively easy to remove systems.

or you can pick on a newer vehicle with r134a system and remove it.

bob g

[mike90045]

I guess you need to figure how you are going to run it, diesel ON all the time, and electric clutch (just like a car install) or autostart the engine, each time the system cycles ?    And then figure the load, do you need 10 hp, or 15 ?
or a hybrid system, where you drive a generator, and charge a battery, keeping engine loaded, and have an electric motor drive the compressor ??

  My head hurts, just store some of last nights global warming, and have a dose of it in the summer...

[Ronmar]

Have you googled some of your questions?  Like "how much horsepower does and automotive AC consume"  or "how many BTU does an auto AC put out"  I have found some interesting information on this subject doing that.  Typical auto AC is going to consume 6+ HP, and it is probably going to give you a comparable BTU output as an electric heater powered from a generator, say 3+kw, or about 2HP per KW...  Auto AC units are typically way oversized for the application, so it dosn't take an hour to get the car's internal temperature under control after teh car sets out in the sun on a hot texas summer day... They typicaly cycle on and off for short periods once teh car temp is in the desired zone.  Basically these parts are required(and this is the flow path as well).  Compressor, Condenser and accumulator/dryer. From here the condensed liquid refrigerant is passed thru a restricted orofice or thermal regulating valve(right at evap inlet), where a metered ammount of liquid is allowed to enter the low pressure evaporator and flash to gas.  From there the evap outlet returns to the compressor to be re-cycled.  You will also need the fans for the evap and condensor, and there is usually at least one control relay and pressure switch which is usually in the vicinity of the accumulator/dryer and a relay.  When the cabin gets cold, the TRV, which has a temp sensor in by the evap coil, starts to throttle the refrigerant flow into the evap.  When this happens, the liquid starts to back up and accumulate in the accumulator, and the pressure builds.  The pressure switch then opens the relay which uncouples the AC clutch and shuts off the condenser fan...  Pressure drops as refregerant is used, switch closes, powering relay and condenser fan and the cold flows once more...        

[BioHazard]

Hmmm....good information. I guess I know just enough to be dangerous.   What effect does varying the RPM of the compressor have? Would it be possible to throttle down the engine to get less cooling?

I thought about trying to pull a complete system out of a car but more and more my body has been objecting to working on cars...especially where they like to hide evaporators.   I'll probably get my shop manual and study the A/C system in my truck.

I totally forgot about the power for the clutch and possibly air blowers, I guess I might have to incorporate a small alternator too. Then I could use electric fans to cool the condensor and push the cold air. I think I'd like to go with an R134A system since that's the easiest refrigerant to find at any parts store.

I'm thinking for engine controls it could be something like an air compressor - when the A/C cycles off, the engine could drop down to idle until it kicks on again.

As usual this project is quickly becoming more complicated, more expensive, and less portable than I expected....


Thanks for the info....

[Tom Reed]

As a firefighter who's had the enjoyment of taking the jaws to a few cars, a skill saw with the new metal cutting blades will just rip up a car in minutes. 

[BioHazard]

That is why God gave us the "jaws of life". Not as much fun but still workable - a sawzall. A gas powered abrasive saw like the fire departments use might work nicely too - who needs to crawl under anything, just slice and dice until just the AC system is left

I think the junk yard might get a little upset with me...I don't think they even allow power drills. 

[vdubnut62]

You could check craigslist and buy a clunker for cheap (it doesn't even have to run), slice and dice, the leftovers will bring around 12 to 14 dollars a hundred pounds.
At least that's  what junk cars bring here. You could even make a few dollars on the whole deal.
I was offered over $800 for my old bus, he hauls it off and I get to keep the front sheetmetal that fits my C-50 dumptruck,
Just saying that it doesn't have to be expensive.
Ron

[BioHazard]

The problem with that is the leftover clunker will probably never leave my property.   I guess I'm a bit of a hoarder. (I've been looking for a bus with some C50 metal too, LOL)

I'm kinda thinking about going with all new components, like maybe a kit for a car, just so I know I can trust it. Not sure if I want to spend that much on something I'll probably rarely use though....

[deeiche]

rm /

[BioHazard]

since you are experimenting, why don't you pickup a cheap window A/C and tear it apart.  The newer one's tend to be relatively efficient.  If you tear one apart you will find the working components aren't really any larger than what you find in an auto.

You can get new 5k BTU units for well under US$100.

Yeah, I've done that before. They make great silent air compressors!  I've got a 5k BTU window unit sitting above the sink in my shop using it as a dehumidifier. I think the evaporators/condensors found in cars are larger though?

[billswan]

Be careful with 134A that stuff is a cancer causer or so I have been told.

Oh and that stuff will burn if it is near a source of ignition.

I believe it is not near so safe as the manufacturers would like us to think.

Billswan

[BioHazard]

Be careful with 134A that stuff is a cancer causer or so I have been told.

Oh and that stuff will burn if it is near a source of ignition.

I believe it is not near so safe as the manufacturers would like us to think.

Billswan

I remember my first experience with an air conditioner when I was a kid...pulling it apart like everything else...."I'll just cut this tube here and...." AHHHHHHHHHH!  Nothing like a face full of R12 to wake you up. Who woulda thought those things were under pressure!