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Do I need 3 condensers or will 2 do?

Hey all,
I live in Florida, as you know it gets pretty hot here but not as hot as Texas. Anyway, I'm ramping up on my A/C project for the 911 and I'm trying to decide if I need another condenser or not. Currently I have one in the rear left wheel well with a fan and a full size one in the tail. I'm considering another in the front fender but that's my question. Do you think I need the last one? By the way I'm planning R134 and a subcooler. Yes they work. I don't really like the underbelly condenser, seems too delicate to be under there like that. And I have an oil cooler under the front bumper so I wasn't planning to put one there.

Thanks for the advice
Jeff
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Old 02-15-2005, 02:21 PM
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Jeff,

The critical issue with the A/C is getting rid of the heat – you can’t have too much condenser. Plumb it so the coolest Freon is at the deck lid condenser.

The other issue is protecting your engine – heat is a killer. Do you have a 1.82:1 11-blade fan? Do you have a full-fin front oil cooler? Are your engine cooler, heads, and cylinders clean?

The 1.82:1 fan arrangement has two benefits. Not only does it cool the engine better at the source of heat but it makes the A/C more powerful.

An additional trick is to buzz along in a lower gear pulling more air across the condenser and engine. At a stop, let the engine rev at 3500. So what if someone notices, you stay cool and preserve the engine.

Best,
Grady
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Old 02-15-2005, 02:42 PM
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Hey Grady,
I'm planning to plumb it to the wheel well condenser first then the deck, as you suggested. I have a 964 motor and I think it has a 12 blade fan. Maybe I'm wrong but I'm sure it has at least 11. I also have a large oil cooler in the front. The engine cools nicely now until I sit still for 20 minutes or so.

So it sounds like you think I need the 3rd condenser huh.
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Old 02-15-2005, 02:59 PM
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In your shoes, I'd get the big, under-belly condenser. Tucking little condensers everywhere isn't as good as dumping off massive amounts of heat with the big guy.
Old 02-15-2005, 03:02 PM
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My car is lowered, do you think I'll still be able to get over speed bumps?

I guess you'll say it depends...
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Old 02-15-2005, 03:09 PM
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Jeff:

I have the stock condensers in the rear deck and at the front of the car, and I added a front left fender condenser and a ProCooler. I'm getting vent temps in the mid-to-high 30s. Though I like the underbelly condenser from Performance Aire, I'm concerned about its durability (despite claims that it's robust), and also about losing ground clearance. Also, it's a passive condenser, so it requires airflow to dissipate heat. If you're in traffic, the heat would radiate updwards, heating your feet.

I'm toying with the idea of adding yet another condenser in front of the left rear wheel, and upgrading the evaporator to a more modern unit.

Keep us posted on your progress!
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Old 02-15-2005, 03:11 PM
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I have four condensor, deck lid, LR wheel well with fan, an 18" square under body that I had lying around and the front bumper one, I get OK cooling, but not great, and I'm using 134a. Here's a tip, buy the hose and fittings loose, fit them in and mark the orientation of the fittings on the hoses with a Sharpie and then have them crimped later. This is especially important if you have any right angle fittings.
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Old 02-15-2005, 03:11 PM
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I agree an extra condenser would be helpful but: "Plumb it so the coolest Freon is at the deck lid condenser."?

Tough to do with a left rear wheel condenser and possible forward condenser. Will add a lot of hose as in an extra loop front to rear. Compressor to left rear wheel well, forward to one of the front wheel wells, back to the deck lid condenser, then forward again to the receiver/drier/subcooler, to the evaporator and then back through the subcooler to the compressor. I think I'd just go directly to the decklid condenser plus put a triplex pressure switch downstream of the compressor to turn on auxilliary electric fans (at an intermediate Freon pressure) on the wheel well condensers and maybe also a fan on the back deck lid if it can be fitted.

Cheers, Jim
Old 02-15-2005, 03:12 PM
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Replace your front condensor with a 964\993 style wheel well condensor. With better efficiency and an electric fan, you can probably do without an underbelly.
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Old 02-15-2005, 03:14 PM
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OK so it sounds like you guys want me to get the other one too... Where do you get the front fender condensers? I know Patrick Motorsport sells one for $300 but a condenser doesn't need to caost that much. I'd rather get a universal one that's cheaper....
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Old 02-15-2005, 03:18 PM
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Quote:
Originally posted by jdowty3
Replace your front condensor with a 964\993 style wheel well condensor. With better efficiency and an electric fan, you can probably do without an underbelly.
Why not just keep both? I took the hose that normally goes all the way from the rear condenser to the stock front condenser and routed it to the new condenser/fan in the front left fender. Then I took the output of that condenser and routed it to the stock front condenser. IMHO, the more condenser surface you have for heat exchange, the better.

I bought my condenser, fan and hoses from www.iceac.com. You can see a picture of it in this thread. The thread also has some good information about adding condensers.
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Last edited by scottb; 02-15-2005 at 03:20 PM..
Old 02-15-2005, 03:18 PM
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Jeff,

Dumb ‘ol me, I just saw the ’84 and not the 3.6L.

I will encourage you to do some experimental work. The air cooling of the engine is critical to its life. Historically the solution has been to build larger and larger oil cooling systems – that is great. I think the air cooling has been seriously neglected. I will speculate it is mostly for reducing fan noise at the expense of cylinder and head temperature. Lets see if an early 11-blade fan (’75-> Turbo) and the large crank pulley will retrofit you your engine. As I understand it, at the same speed the curved blade fan pumps less air but is quieter. This is not desirable for Florida, Texas, SoCal, and certainly not Colorado thin air.

Can you find access to the earlier parts?

The additional benefit is it pulls more air across the deck lid condenser.

I assume you already have a Factory front condenser.

The LR condenser is the best place to expel the highest temperature heat. Partially because it is close to the compressor but also it is in a hot environment and the heat exchange is temperature differential dependent. I would normally choose the deck lid condenser to be last in line to avoid heat input to the engine. With three+ condensers that puts another up front. There is a lot of plumbing but not all bad.

Yes, use the second evaporator/radiator in the return line. If I were designing a system, I would put it behind the driver’s seat with a small fan.

I think it is reasonable to design an A/C system for an old 911 (’78-’89) that rivals anything in the world. This is very worthwhile for daily drivers in hot weather. In LA, Houston, DC, or Miami I would want to be able to take clients out for lunch and visit whatever sites in a nice old 911 in comfort and without the fear of a problem.

Nothing like a 3.6 to keep their attention.

Best,
Grady
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Old 02-15-2005, 03:58 PM
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"The LR condenser is the best place to expel the highest temperature heat. Partially because it is close to the compressor but also it is in a hot environment and the heat exchange is temperature differential dependent." ??

At face value this statement violates the 2nd law of thermodynamics (heat flows from high temperature to low temperature). Now if you mean that the LR wheel well area is already hot due to the catalytic converter, exhaust, etc. and the extra heat from the condenser does less harm to the engine here, I agree. However, this location is a lousy place for a condenser as it's breathing hot air and looking at hot surfaces (at least I think Clausius would think it a poor location).

Cheers, Jim

Last edited by Jim Sims; 02-15-2005 at 05:19 PM..
Old 02-15-2005, 05:04 PM
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Grady,
I don't have a front condensor. My car did not originally have A/C so no place for it. I have an oil cooler under the front bumper where I could have stuck one otherwise. I'm interested in the retro fan option but will reserve that for later if I need more cooling.

So my current plan is compressor-> rear fender->rear deck lid->front fender->procooler->expansion valve. So far I'm not keen on the spagetti required to make the rear deck the last condenser but I do understand the suggestion and thanks.

Jim,
I think I'm going to put the rear fender condenser in front of the tire, it should be cooler there than behind.
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Old 02-15-2005, 05:29 PM
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Do you guys have the drier on the hot side?
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Old 02-15-2005, 05:30 PM
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Receiver/drier (or procooler if that's what one is using for a combined receiver/drier/subcooler) is typically located just upstream of the evaporator expansion valve which could be considered the "hot or high pressure" side. Jim
Old 02-15-2005, 06:40 PM
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Jim, that's what I was thinking, sort of. I'm planning to use one of your favorite $16 suction line heat exchangers (I read your post about it). So I'm thinking I'll go
last condenser->drier->procooler->expansion valve
as that's the easiest routing for the hoses as far as I can tell right now.
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Last edited by jfpound; 02-15-2005 at 07:04 PM..
Old 02-15-2005, 07:00 PM
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If you're making a custom setup you can get a new receiver/drier from NAPA for about $30; they can be had with either flare or o-ring fittings. Don't waste $90 plus on one of the OEM Behr receiver/driers unless you really need it's slim design to clear a wheel assembly. Jim
Old 02-15-2005, 07:06 PM
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Jim did you have any issues yet with cracks in your subcooler setup? I only ask because copper isn't the best for vibration.
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Old 02-15-2005, 07:07 PM
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Not yet; one system has now been leak tight for a year and a half. It was doing well last summer in Needles, CA with 115F air temperature - temperature had to be turned down during highway cruising. The other system is open because I painted the car and took the condenser off the back deck lid during painting. My subcooler installations have hose on both sides and padded mounts to somewhat isolate them from vehicle vibration. The A/C system pressure cycling fatigue loads are still there (as they would be in the original stationary application that the subcoolers are designed and sold for) though but so far so good.

Hopefully the vendor of these subcoolers won't discover they're being installed on 911's otherwise they'll raise the price by a factor of five! Jim

Last edited by Jim Sims; 02-15-2005 at 07:19 PM..
Old 02-15-2005, 07:16 PM
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