Learn me A/C systems?: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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April 10, 2011 5:13 p.m. JamesMcD New Reader

Maybe not exactly GRM related, but...

If one's automobile has all the stock A/C components on the interior side of the firewall, but nothing on the engine side, how reasonable is it to expect to be able to cobble up a custom A/C system using, perhaps, "junk-yard" components from other cars, and off-the-shelf fittings and adapters? The principles of A/C are the same across varied makes and models so in my head this seem to be a possibility.

I am asking this in reference to my FD (3rd gen. RX-7) because the A/C bits changed several times across the years and it is difficult to collect all the pieces if you have a certain iteration (also, some parts are obsolete). So I'm contemplating finding a compressor, condenser, etc. from perhaps another Mazda, and having some custom lines made up to create my own system. I can't think of why this would not be feasible. Custom bracketry is no problem as I do CAD in a sheet-metal-related industry.

James
April 10, 2011 7:58 p.m. Curmudgeon SuperDork

Not a guru, I just see a lot of A/C work. First: yes it is very possible to cobble up a nice system from parts scavenged from various cars. The toughest part will be getting an evaporator that fits properly. Easiest way: get the proper evaporator, then mix n' match the other components to fit.

To help out a R134 conversion, unfortunately adding more refrigerant won't help the situation. For instance, most R134 swaps use roughly 85% of the original R12 charge. The accumulator is not the solution either. The fix is an evaporator and condenser with more surface area. That has a lot to do with why evaporators went from the coil and fin type to the 'stacked plate' aluminum versions.

If the cars in question do not have tinted windows, dark tint is a real good place to start. Come to think of it, I need to re tint the Trooper.

If you really want to increase the output of your R134 system, see if a later version of your car used R134 then get that evaporator and condenser. You'll need to get the evaporator case too. Go to the larger condenser also, or add a small secondary condenser (this means fabricating hoses etc) and you should see a change. But do not expect the world; R12 would get down to the mid to high 30's at the center vents under ideal conditions, R134 is doing good if it hits low to mid 40's. Doesn't sound like much but yes it is very noticeable.
April 10, 2011 9:00 p.m. corytate Reader

shouldn't be any harder than changing r12 up to r134, which is supposed to not be difficult I have my 609 but haven't done ANY AC work lol
April 10, 2011 9:14 p.m. Derick Freese Dork

Doing the little bit of phase change overclocking that I've done, I can tell you that you can mix and match parts. Think of it as a separate system. As long as you have an adequate condenser and an adequate evaporator and a compressor big enough, it will work fine. Mounting will be your biggest issue.
April 10, 2011 9:27 p.m. curtis73 Dork

I recommend going over to vintage air's site and clicking on pages 6-9. They have an excellent beginner writeup on how to select components. Then you can find the specs of what you have and match up properly sized missing parts from the junkyard.
April 10, 2011 9:52 p.m. jhaas Reader

i made my own AC system in my 64 buick wagon. getting all the fittings to agree will be the only hard part.

i used the ls1 ac compressor, the old 64 dash mounted evap, and a condenser from a mitsubishi pick-up. i had to weld my connections onto alot of the aluminum ac lines. works great and looks stock.

on another note. could a fin style AC condenser work as a transmission cooler? i have a volvo 850 givin me fits when the transmission gets hot. i put a small gm cooler on it. it helped but if i run the AC also the trans starts to slip. when it cools off everything is fine.
April 10, 2011 10:02 p.m. internetautomart SuperDork

If you still have the parts for the interior (in dash) then it's not that hard. The condensor can be bought to fit, lines fabbed, compressor get one that is the same style as matching the brackets you have. you will need some sort of expansion device. IMO I would use an old school Orifice tube. They make some that are specifically designed for retrofitted systems. Make sure you don't overbuild the system. Frozen evap doesn't cool very well.
April 10, 2011 10:52 p.m. friedgreencorrado SuperDork

Derick Freese wrote:

Doing the little bit of phase change overclocking that I've done, I can tell you that you can mix and match parts. Think of it as a separate system. As long as you have an adequate condenser and an adequate evaporator and a compressor big enough, it will work fine. Mounting will be your biggest issue.

So I can keep the original compressor/dryer/etc.(which I was afraid to replace, since replacing those would be difficult to find room for under the hood, etc. , and just mount bigger condenser/evaporator units somewhere in the airflow? Hey, maybe I can just mount them on either side of the oil cooler.

Or maybe not..space is kinda tight down there (just like you said). I'd end up with either exposed coolers like the import drag crowd, or having the units mounted so low that I'd fracture them on every big bump. Thanks for the advice, though..you know a lot more about this than I do.
April 11, 2011 1:26 a.m. curtis73 Dork

jhaas wrote:

on another note. could a fin style AC condenser work as a transmission cooler? i have a volvo 850 givin me fits when the transmission gets hot. i put a small gm cooler on it. it helped but if i run the AC also the trans starts to slip. when it cools off everything is fine.

In a word, probably not. Ok, that was two words. An A/C condenser works in higher pressures and the focus is on surface area, heat transfer, and not on flow. Transmissions send low pressure fluid to the cooler (typically in the 20-40 psi range). They rely on flow. Potentially restricting flow with an A/C condenser could be rather catastrophic.

At any given time, that huge condenser is responsible for moving very tiny volumes of gas/liquid at pressures that can be well over 100 psi. Trying to force a viscous liquid through it with only 30 psi to push it isn't a wise move.
April 11, 2011 6:17 a.m. jhaas Reader

^^ i was afraid of that. makes sense.
April 11, 2011 8:37 a.m. pres589 Dork

In reply to jhaas:

Not to threadjack but I personally would start searching the B&M catalog for coolers and possibly consider a pair of smaller coolers so they're easier to place in the car.
April 11, 2011 1:50 p.m. jhaas Reader

yeah, i just dont want to drop $100 plus on a cooler. i got a larger trans cooler of a 99 2500 ($11). hope it does the trick. and im gonna fill it with amsoil ATF.
April 11, 2011 2:35 p.m. friedgreencorrado SuperDork

curtis73 wrote:

I recommend going over to vintage air's site and clicking on pages 6-9. They have an excellent beginner writeup on how to select components. Then you can find the specs of what you have and match up properly sized missing parts from the junkyard.

Bookmarked. Thank you.