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Da_Hose
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Air conditionin function overview and retrofit/repair thread

Post by Da_Hose » Sun Jun 16, 2013 6:18 am

Ok, everyone. I have recently done A LOT of research on air conditioning and have seen some really useful stuff in another thread. That made me think we should have a thread designed to help us understand how our air conditioner systems work and what retrofit/upgrade options are available for our A/C systems.

I am starting with the information below, which is borrowed from another thread. It gives an overview of the dual A/C systems and explains why an undercharged system can cause the rear to blow cold while the front blows only cool or luke warm. (borrowed content starts now).


Familiarize yourself with the system a little bit first, by referring to the attached diagram.

The small tubes are the high pressure lines (Red) and the larger are the low pressure return lines (Blue). The small Line from the Receiver/Drier (Ref #9, front A/C) splits the high pressure line to the front and back evaporators and the hose, (Ref #2, front A/C), "y's" together the front and back return lines before feeding into the Regulator (Ref #3, front A/C).

You can see the pressure sensing tube (Ref #15, front A/C) coming off the top of the regulator which screws into the coiled tube to the left on the front expansion valve (Ref #5, front A/C). The other tube, to the right of the expansion valve, is the temperature sensing line.

The rear "H" expansion valve (Ref #6, rear A/C) senses pressure and temperature internally right at the inlet and outlet of the rear evaporator.

The electrically operated valve in the rear (Ref #4, rear A/C) cycles the high pressure refrigerant to rear A/C on and off as the rear temperature control call for.
____________

The explanation:

The high pressure refrigerant lines are split and routed to both the front and rear evaporators. The rear uses a standard "H" expansion valve that senses the output pressure right at the evaporator to regulate the input for maximum cooling. The low pressure return lines from both evaporators "y" together before being fed into a regulator that maintains the proper system pressure for the compressor regardless of whether the front, the rear, or both evaporators are cycling on or off. The front evaporator's expansion valve, however, does not sense the pressure at the exit of it's evaporator, but rather it samples the total system pressure at the regulator. Now, in the case of an undercharged system, where there is not enough refrigerant to run both expansion valves at their max opening for full cooling, the regulator throttles back to keep up the pressure and the front expansion valve senses this and closes to match it while the rear continues to operate at max if it is called for. (This explanation is highly simplified)
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Post by Da_Hose » Sun Jun 16, 2013 7:04 am

Ok, then. Next chapter. This is also a long post, so hold on tight.

Retrofitting your less than perfect A/C to a different refrigerant is actually a pretty good idea. Recharging with R12 is getting EXPENSIVE because current R12 supplies will eventually run out and there will be no more available for our original A/C systems. The "typical" retrofit route is to do an R134A conversion. Mind you that the original pump is designed for R12, so it won't be as efficient, but it SHOULD still real cold. There is also a second option, but this post will deal with the most common retrofit route first.

To change out to R134A, there are two paths. You can do a FULL conversion which includes installation of an R134A conversion kit (two small adapters that thread onto the existing R12 fill fittings), a new receiver/dryer, a new R134a compatible compressor, a new condenser for the front of the car (in front of your radiator) and new expansion valves for your condensers inside the car. That is all pretty expensive, so many folks will opt to just do the R134a adapters, new receiver/dryer and changing out the mineral oil in their original pumps to an R134a compatible oil. Keep in mind that a system designed for R12 is not as efficient when running R134a, so those of you in HOT areas might find that only changing out the gas and receiver/dryer will not perform well enough for you (YMMV).

Once you have picked your upgrade route, getting the parts is up to you and your available resources. Getting R134a refrigerant with a charging hose, the conversion kit/fittings and the correct oil should be as easy as stopping by your local auto parts place. You use 85% as much R134A vs. R12, so read your under hood sticker and calculate recharge volume accordingly.

If you still have R12 in your system, remember that in the U.S. (and many other countries) it is illegal to vent R12 from your A/C on purpose. Contact a local A/C repair shop and ask them to evacuate your system. They can charge big bucks for your old Freon, so they might do it for free. Once your system is empty, you can replace all the parts, but change out the receiver/dryer last. It needs to stay as moisture free as possible.

Once all parts are installed, you need to vacuum the system out. If you have a powerful compressor at home, then you can purchase a compressor powered vacuum pump and an A/C service manifold from Harbor Freight, or some other local tool supplier. If you don't have a good compressor, then you can buy an electric vacuum pump from HF for about $90. You will also need an A/C service manifold to be positive the system has gotten down to the right vacuum level. HF also sells a decent A/C service manifold. I'm not associated with Harbor Freight in any way. I am just a tool whore :lol: The tools I recommended above are of decent quality for home shop duty and are really affordable through HF. Once you have the tools, connect the service manifold or vacuum pump as appropriate and pull vacuum down on your system to at least 24" in/HG (preferably 28 or more) and then sustain that vacuum draw for about 10 minutes to boil out any and all moisture. When you are done boiling out the moisture, close the valve on the service manifold and disconnect the pump. Ensure the vacuum gauge doesn?t drop in reading for at least 30 minutes. That tells you the system is completely sealed and ready to be charged. If the reading drops, find and fix any leaks. When you can sustain the vacuum level, you are ready to recharge with refrigerant and oil.

Follow the instructions for whatever charging system you are using and don?t forget that you need to add the appropriate amount of oil. Often times, the auto parts store you are buying from can tell you how much R12 your system holds.

Jose
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Post by Da_Hose » Sun Jun 16, 2013 10:33 am

Chapter three - one more folks. Hang in there.

Now .... in the last post I said there is a much less common retrofit alternative for an R12 based A/C system. There is a kind of fringe user base for HC-12a. HC refrigerants have been tested and used in commercial applications for a long time, but they have never been fully approved for automotive applications in the U.S. It seems to be allowed in other countries, though. The biggest positives about HC refrigerants include being environmentally friendly. They also seem to perform better than R134 and WAY better than the original R12. A well known brand for HC refrigerants is DuraCool, but others exist. The single biggest negative is that HC-12a is a mixture of isobutane and isopropane, which makes HC-12a very similar to the propane used for a gas grill. That means HC-12a is quite flammable. While the auto ignition temp. of HC-12a is upwards of 1600 degrees (that means spontaneous combustion), it's still a hydrocarbon and will ignite from an open flame.

Why is HC-12a appealing as a refrigerant for conversions? Well, first off it is more efficient than R12. It gets your air colder faster and compared to R12, you only need about 35% as much by volume. HC refrigerants are also non-corrosive and won't react with any moisture that might still be in the system. Last but definitely not least, HC refrigerants are also a direct drop in refrigerant. You literally do not need to make ANY modification to your existing system. HC-12a can be added directly into an R12 OR R134a based system. Theoretically, you don't even need to change the type of oil in the system. That is probably the biggest appeal. You do not need to replace ANY parts in a well working R12 or R134a system when you convert to HC based refrigerants. If you have gas in your system, then have it purged and vacuum tested. If it holds the vacuum, then you could just refill with HC-12a. As I understand it, the HC-12 molecules are also bigger so you get better mileage when running your A/C, because it takes less power to run the compressor and you lose less of it through the hoses and seals.

So then, if it looks so good on paper, why isn't everyone running HC-12a? Well, there are a host of political and financial reasons that cause a lot of debate, but safety (fireball) is the single biggest concern raised by anyone who opposes using HC based refrigerants in cars. What is interesting is that in Australia there was an off road truck manufacturer (OKA) that ran HC-12a in their production trucks for about 4 years (2007-11). I can't find any info. about them going up in flames, which indicates safety might have been good. OKA is the only example I can find of an OEM actually using HC-12a. Australians seem to have been using HC-12a in cars for a while and I understand that Canadians can buy HC-12a in their local auto parts locations, mainly because HC-12a is truly a "green" alternative. I can only find one documented case of a lawsuit in Panama related to using HC-12a in a bus, but that seemed to be more an issue of gross safety violations piling up. I also found some comments about A/C techs. getting hurt when they didn't realize there was an HC based refrigerant in the car they were working on but no articles. There is also a video on youtube of an Australian researcher who set off a couple cans worth of HC-12a in a car and created a good sized fireball.

Ok, then. Let's say you have balanced risk/gain and want to try HC-12a. What are the sticking points? In some states HC based refrigerants are illegal altogether. In California, you can legally convert a vehicle from R134a to HC-12a. You CANNOT convert from R12 directly to HC-12a. You must have already converted for R134a first. That means you have to install the R134a conversion kit (the two adapters) and the sticker.

What I come up with by sort of extrapolating some general numbers, is that there are probably tens of thousands of people across the major industrialized countries who are running HC based refrigerants in their cars and doing so without incident. There are probably a whole lot more users in non-industrialized countries running it, because its cheap. I also find many web sites where people comment that they have been using HC based refrigerants for years and will continue to do so. I cannot find a successful lawsuit against HC-12a manufacturers, though. HC based refrigerants are certainly something that interests people and seems to work. Caveat emptor as they say.

Personally, I find the larger volume of refrigerant that my dual system uses and the close proximity of the refrigerant lines to the HELLISHLY HOT exhaust header a combination of factors that would keep me out of HC refrigerant territory. I have to admit that I would be tempted to use it in the motorhome where the condenser, pump and receiver/dryer are all at the front of the engine bay where any leaks could vent quickly.

Jose
Last edited by Da_Hose on Sun Jun 30, 2013 8:13 pm, edited 1 time in total.
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Post by Shuttleman » Sun Jun 16, 2013 3:09 pm

I'm trying to find info on readjusting the under-hood regulator. Any help?

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Post by Da_Hose » Sun Jun 16, 2013 10:09 pm

In function, the high/low pressure differential is what governs how cold your A/C can blow. So what you want is for your low side pressure to live somewhere in the 20-30psi range. High side pressure will vary but should generally be in the 200-250 psi range. More than 300 and something is probably not right.

We know that the regulator at the y-fitting controls how much pressure goes to the pump. If you are concerned that someone monkeyed with that regulator, then you should connect a low pressure gauge to the low side of the system, after the regulator. Then adjust the regulator so that your pressure is about 20psi. If your high side pressure starts going out of the high range before you get to your desired 20psi., then you would need to reduce the amount of gas in the system. If you can't get to a high enough pressure on the low side, you probably need more gas.

Does that help?

Jose
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Post by Shuttleman » Sun Jun 16, 2013 10:26 pm

Yes, thanks Jose.

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Post by Da_Hose » Fri May 16, 2014 6:20 am

Hey, folks. I was doing some AC work today and decided to revisit this thread. In working with a "real" AC manifold (bought it at HF), I paid extremely close attention to my gauges and pressure readings.


Ok, I will explain what I did today. Temperatures have spiked here in the valley and we are getting high 90F degree days. I have been experiencing the dreaded, warm front A/C, so I hooked up my manifold and tried checking my pressure differentials. When I took off the low side cap at the regulator/splitter, it popped the cap off into my hand and I could hear it hissing. I was now 100 percent confident that my A/C was blowing warm in the front, because the system was low on gas. I will have to drain the system to change the adapter fitting that is connected at the regulator/splitter. That can happen at the end of the season.

What I have learned in this process is that there is no set pressure that all systems can be expected to run at. They ALL vary and checking static pressure is near useless. You MUST check while the engine is running. Another thing I learned (I have been doing a fair bit of reading) is that there is lots of misinformation out there, which is particularly problematic as BMW does not recommend you fill by pressure. BMW recommends you evacuate the system completely, then add a specific volume/weight of oil and gas. So how do we work around this issue with a manifold gauge? Well, here is the nominal pressure chart for an E24.

Image

Keeping in mind that 1Bar = 15 psi, we see that the high pressure side acceptable range goes from a low of 150 psi at 60F ambient, to a high of 390 psi at 104F F ambient temp.

Ok, so what did I actually do to get the front condenser blowing cold? I went to Orielly today and bought two cans of R134. I then started up the engine and when I hooked up my manifold, I saw that the low side was hovering around 10 psi and the high side was around 150. It was over 90 degrees outside and the headers make everything on that side of the engine CRAZY hot, so I don't know that I can trust any scale of pressure vs. heat. I proceeded to add R134 a little at a time to inch my way to the right settings. At an idle, the air started blowing nice and cold from the front grille when the low side pressure hit about 15 psi and the high side was a little over 200. I continued adding refrigerant to the low side at that point, but forgot to open the high side valve. When I noticed my mistake, I had already put in almost all of the second can and the pressure was at about 250. The system was still blowing cold and things seemed good to go. However, when I turned off the engine I could see the compressor turning backwards very slowly and heard some gurgling. I did NOT like the look/sound of all that, so I decided I had to vent pressure. I evacuated out some gas and started the engine back up. I continued releasing pressure until I hit about 200 psi. on the high side and left it there. I didn't test with my IR thermometer gun, but my super-senso-finger meter told me that there really doesn't seem to be a benefit to increasing the pressure beyond 200 or so on the high side.

I did some looking on youtube and saw an A/C troubleshooting video by a guy who runs a shop.

https://www.youtube.com/watch?v=i9yv0euT7xA

He sums it up with the following statements.

Run up the idle to about 2000 rpm and look at your gauges. The below conditions mean ....

Low side (low pressure) and high side (low pressure) = low charge

Low side (low pressure) and high side (high pressure) = blockage in system (expansion valve)

Low side (high pressure) and high side (low pressure) and needle jumping = faulty reed valve in compressor (particularly if the needle pulses)

Low side (high pressure) and high side (high pressure) = system overcharged

This weekend, I will test again with a heat shield in place and by using the factory R12 fitting that is inline, BEFORE the regulator/splitter. That will give me the actual reading coming off the pump. I might even take some pictures of my gauges all hooked up. What I can say for sure is that my A/C is blowing nice and cold now.

Jose
Last edited by Da_Hose on Tue Jan 08, 2019 3:57 am, edited 1 time in total.
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Post by BlackBetty » Fri Jul 11, 2014 12:08 am

In addition to Jose's excellent write up above here is a link to a PDF for the wiring diagram for an '89.. Section 6400 shows the heating and A/C system , as well as a troubleshooting (electrically) chart on the back of that chapter.
Might come in handy for someone as they are working on their AC system..
http://wedophones.com/Manuals/BMW/1989% ... Manual.pdf

Pete

Ps, maybe a good one for the technical section??
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Post by Chris Wright » Fri Jul 11, 2014 12:46 am

BlackBetty wrote: Ps, maybe a good one for the technical section??
The ETM download for all of the years is already in the Tech section. You've seen this link haven't your?

Check out this Posting for links to Factory WorkShop Manuals, Wiring Diagrams (ETM's), Factory Parts Catalogs, parts Suppliers etc.:
viewtopic.php?t=10410
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Post by Da_Hose » Mon Jul 06, 2015 7:40 am

I am reviving this thread because I am making new custom hoses for my AC and there is some shit that is royally pissing me off. I hope to save others some frustrations.

FIRST!!!

NOBODY has bothered to put fitting sizes up, so others can try to get parts ahead of time and not take extra freaking days to complete the damned job!

So then ..... on my 1987 M6, the hose connecting to the regulator on the low side is a #10 fitting. The other end of that hose connects to the compressor low side port with a #12 fitting. The wrench size for the compressor fitting is huge. I think it's a 28mm or 30mm. A 10" adjustable wrench worked for me.

The high side hose connecting to the condenser (you can get to the connection behind the passenger side headlight grill) is a #8. The fitting at the compressor is also a #8.

All my hoses were modern, o-ring type. Something to realize is that the compressor is crammed into a small space and you can't get wrenches on the compressor. My guess is that it takes specialized tools to get those loose with everything mounted.



My specific setup is built around Aeroquip EZ-Clip style connectors and regular barrier hose.

At the regulator end of the low side hose I used a 90 degree, #10 fitting with low side test port. The other end of the hose is a 45 degree #12 to #10 insert adapter on the compressor and a #10 female fitting (regular nut) on the hose.

The R134 conversion was already done when I got the car, so I don't know what hoses are original. The compressor has very useful hard line that does a 180 degree turn, then goes down below the compressor and turns at 90 degrees facing the back of the car. That allowed me to use a 90 degree #8 fitting to bring the line back up and forward to the condenser. At the condenser, I used a 45 degree fitting that came with the kit I bought, but I might be changing that out to a straight and shortening the hose. The condenser has a #8, fitting. I will add pics. to this post when it's all assembled.

Jose
Last edited by Da_Hose on Mon Jul 06, 2015 6:55 pm, edited 1 time in total.
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Post by slofut » Mon Jul 06, 2015 11:47 am

Da_Hose wrote:I am reviving this thread because I am making new custom hoses for my AC and there is some shit that is royally pissing me off. I hope to save others some frustrations.

FIRST!!!

NOBODY has bothered to put fitting sizes up, so others can try to get parts ahead of time and not take extra freaking days to complete the damned job!

So then ..... on my 1987 M6, the hose connecting to the regulator on the low side is a #10 fitting. The other end of that hose connects to the compressor low side port with a #12 fitting. The wrench size for the compressor fitting is huge. I think it's a 28mm or 30mm. A 10" adjustable wrench worked for me.

The high side hose connecting to the condenser (you can get to the connection behind the passenger side headlight grill) is a #8. The fitting at the compressor is also a #8.

All my hoses were modern, o-ring type. Something to realize is that the compressor is crammed into a small space and you can't get wrenches on the compressor. My guess is that it takes specialized tools to get those loose with everything mounted.



My specific setup is built around Aeroquip EZ-Clip style connectors and regular barrier hose.

At the regulator end of the low side hose I used a 90 degree, #12 fitting with low side test port. The other end of the hose is a 45 degree #12 fitting.

The R134 conversion was already done when I got the car, so I don't know what hoses are original. The compressor has very useful hard line that does a 180 degree turn, then goes down below the compressor and turns at 90 degrees facing the back of the car. That allowed me to use a 90 degree #8 fitting to bring the line back up and forward to the condenser. At the condenser, I used a 45 degree fitting that came with the kit I bought, but I might be changing that out to a straight and shortening the hose. The condenser has a #8, fitting. I will add pics. to this post when it's all assembled.

Jose
Thanks MUCH for posting this Hose! Your time and frustration are appreciated. =D>
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Related sites

Post by sansouci » Tue Jul 07, 2015 1:24 am

Classic auto air
Denlors tools
POLAR Bear inc.
O-rings west
Moreland hose and belting
The o ring store
  • Some useful and not so useful stuff for air con
Sansouci
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Re: Related sites

Post by slofut » Tue Jul 07, 2015 1:37 am

sansouci wrote:Classic auto air
Denlors tools
POLAR Bear inc.
O-rings west
Moreland hose and belting
The o ring store
  • Some useful and not so useful stuff for air con
Bought a retrofit firewall forward kit from Classic Auto Air for my 71 vette/LS1. Has adapter pipes made to fit to the universal condenser, about 12-15 inches long. Very similar to what would work on the e24...
Nice kit, quality parts and perfectly worked out to fit, from compressor brackets to hoses. No affiliation, just a happy customer.
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'75TR6
'64 Olds 88 conv
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Post by jacko » Tue Jul 07, 2015 7:49 pm

So, if we are going to go for new hoses with a universal condenser, all we should need, aside from any changes in length is to have them made up oem on one end and maybe a 90 or 45° fitting to fit the condenser on the other.
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Post by slofut » Tue Jul 07, 2015 8:14 pm

jacko wrote:So, if we are going to go for new hoses with a universal condenser, all we should need, aside from any changes in length is to have them made up oem on one end and maybe a 90 or 45° fitting to fit the condenser on the other.
That's if the hoses will make the bend out of the sheet metal and to the condenser ports. Might require short hard lines bent to bring the ports up to where the originals are. Don't have a car apart at this time so I can't be sure , but the last time I looked this over I'm pretty sure I found the bends too tight for continuous lines. Hope I'm wrong...
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'75TR6
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Post by Da_Hose » Wed Jul 08, 2015 12:59 am

A soft, #8 hose and connector will make the bend just fine if coming off the oem fittings.

Matter of fact, I have been looking at parallel flow condensers. Many of them come with mounting kits that would let you easily adapt them to any car. If I had to convert right now, I would buy a generic, parallel flow condenser of the correct size, with outlets straight out the side, then use 90 or 45 degree connectors and route the hoses to the compressor and drier.

When I post my pictures it will be clear why the hard line on the compressor is a really good way to fit everything together.

Jose
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Post by six shooter » Thu Jul 09, 2015 11:36 pm

I understand the parallel flow condensers are NLA.
I looked into aftermarket units. If I were to do it again,
I would find a really big condenser and mount it.
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Post by Da_Hose » Fri Jul 10, 2015 12:58 am

This is what I'm talking about.

http://www.ebay.com/itm/New-Universal-A ... d3&vxp=mtr

Install the right size condenser, put 45 degree connectors on the hoses, pull the hose ends to the compressor and drier. You will also need a 90 degree on the compressor end and maybe another 45 or 90 on the drier end. Fittings would be about $15 each and hose would be about $4 a foot for small, bulk cut pieces. Figure about $50 per hose.

I just ordered a custom compressor adapter for $35 shipped from a shop in Fla. So now we have a supplier that can make any adapter or complete hose that we might need. Hell, I will have so much hose left over that I could make a couple custom lines for people.

Jose
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Post by six shooter » Fri Jul 10, 2015 1:24 am

I know the parallel flow condensers I had were same size as factory.
Does this unit have the same area?
The aux fan bolted right up.
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Post by dwcains » Fri Jul 10, 2015 3:18 am

You can certainly fit a much larger condensor, and the PF one I have is 16 x 22", which is ~45% larger. Heat exchange is all about surface area.
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Post by dwcains » Fri Jul 10, 2015 3:26 am

My car is an '85, so it has no rear A/C. When I bought the car it had a non-original compressor (unknown brand) and no special hard lines or adapters on the compressor fittings. Nothing special will be required for the Sanden compressor, either, except a 45-degree fitting one one hose and a 90-degree on the other.
Da_Hose wrote:This is what I'm talking about.

http://www.ebay.com/itm/New-Universal-A ... d3&vxp=mtr

Install the right size condenser, put 45 degree connectors on the hoses, pull the hose ends to the compressor and drier. You will also need a 90 degree on the compressor end and maybe another 45 or 90 on the drier end. Fittings would be about $15 each and hose would be about $4 a foot for small, bulk cut pieces. Figure about $50 per hose.

I just ordered a custom compressor adapter for $35 shipped from a shop in Fla. So now we have a supplier that can make any adapter or complete hose that we might need. Hell, I will have so much hose left over that I could make a couple custom lines for people.

Jose
Dean
Lutz, FL

'85 635 CSi Euro #9402254
'87 Spider Veloce
'92 Spider Veloce
'08 350Z

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six shooter
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Post by six shooter » Fri Jul 10, 2015 3:52 am

dwcains wrote:You can certainly fit a much larger condensor, and the PF one I have is 16 x 22", which is ~45% larger. Heat exchange is all about surface area.
Show me the area!!!!!!
Red 1987 //M6 (sold)
1986 635 (sold)

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dwcains
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Post by dwcains » Fri Jul 10, 2015 4:46 am

I've posted this pic before:

Image

I think it's got 37 or 38 tubes (eBay picture shows 24 tubes), and overall it's about the same size as the OEM serpentine condensor. Looks like it started out as a universal type, as you can see the outside frame with multiple mounting holes. What Classic's manufacturer did was weld on the mounting brackets, fan bracket, and hard lines to mate with the original hoses.
Dean
Lutz, FL

'85 635 CSi Euro #9402254
'87 Spider Veloce
'92 Spider Veloce
'08 350Z

Image

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dwcains
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Post by dwcains » Fri Jul 10, 2015 4:55 am

This one may be the same core, I guess it depends on how you measure, but it's got the same number of tubes as the one from Classic. And, lots if $$$ left over to fabricate your own brackets and hoses/adapters.

http://www.ebay.com/itm/New-Universal-A ... 0022[/img][/url]
Dean
Lutz, FL

'85 635 CSi Euro #9402254
'87 Spider Veloce
'92 Spider Veloce
'08 350Z

Image

m6dave
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Post by m6dave » Fri Jul 10, 2015 9:23 am

dwcains wrote:This one may be the same core, I guess it depends on how you measure, but it's got the same number of tubes as the one from Classic. And, lots if $$$ left over to fabricate your own brackets and hoses/adapters.

http://www.ebay.com/itm/New-Universal-A ... 0022[/img][/url]
I bought a universal condenser from this company and the quality is excellent. Mine is a 14" x 20" but the 16" x 19" would have been better. It will be installed soon with the new Sanden compressor, I'm watching Jose's hose system as the final part of the puzzle.

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