AC upgrades/improvements
 

Heat wave here in So. Cal... Ouch. I had to aim my fan at my cable modem just to read this board; it drops my connection when it gets too hot!

My 300TD was converted to r134a at the end of last summer... The AC didn't work at all for years before that, and it wasn't very hot in October so the conversion seemed fine to me. And it is... if you're sitting in the front seats, and the temperature doesn't get above 85.

Yesterday and today made me decide I need to do something to improve the AC - either convert back to r12 or do some kind of upgrade (or both).

Searching the board, I found plenty of references to r134 -> r12 (re)conversions. I also found lots of talk on upgrades (bigger compressors, parallel flow condensers, better fans) but nothing apparently concrete on that subject (nothing from anyone that's actually tried it).

Parallel flow condensers and a better fan sounds like a worthwhile upgrade. Leathermang was talking about doing it in this thread:
http://www.peachparts.com/shopforum/diesel-discussion/65377-increasing-air-conditioner-reserve-capacity.html?perpage=15

Does anyone know how that went? Can you use a parallel flow condenser with an r12 system (it sounds like they're just meant for r134, but I hope that's not true; it would be nice to have the advantages of both!).

Anyone have any thoughts/comments/advice on this matter?

I have done the following to my 1984 300SD:

1.) parallel flow condensor (largest I could fit) with custom hoses and a little minor metal cutting to get it all in.

2.)auxilliary fan on relay circuit to compressor clutch, and adjustable temperature circuit as well, for fan engagement.

3.)adjusted evap temp sensor (small screw inside it) to ~34ºF (had it too low when I initially adjusted it and frosted the evaporator all the time).

4.)NEW R4 compressor (an ebay find, cheap), NOT rebuilt.

5.) Set up for R-12, but currently running "test" refrigerant (I'm not a proponent, so don't go there!). I put it in to check out the system for leaks or problems, but haven't found any problems, so haven't got around to evacuating, vacuum and recharge with R-12 (I have a small supply of R-12 hidden away).

6.)Replaced some pods when I had the dash out so I know all is well with air distribution.

7.) electric sun shade from an ~1989 560SEL. This has been the absolute best thing to keep the car cool and really helps "pull down" time!!!

8.)refilled the main fan clutch with 6000 cst silicone oil and shortened the pin under the bimetal strip to insure clutch engagement when warm.

Things still to do:

1.)window tint

2.) get the R-12 in it.

3.) recirculation mod of the switchover valves to the pods of the fresh air door.

In July at 105ºF going up the Sherwin Grade to Mammoth, the car was cool as a cucumber.

This heat wave is something for this time of year isn't it? If you want to talk about it email me your # and I'll call and share my tribulations of searching for the perfect walk in freezer on wheels.

81Wagon, you don't need a Bigger compressor... just a good one in good condition....

Jbaj007, Tell us more about the electric sunshade... I have never seen or heard of it.... any picture available?

Can you post pics of your mods. Looks like an interesting project.

Sorry, I don't have pictures. I'll try on Friday to snap some.

The electric sun shade is a factory option for 1987+ long wheel base and coupes (different length rail for the coupe, but that's the only diff.). It fits on the standard 87+ parcel shelf and there are cut outs in the shelf already for installation. Wired to a polarity reversing switch (extra sunroof switch). One of the guys on the mbcoupes mail list did it and wrote it up so I found one at the wreckers and tried it. Section 68, subsection 600, # Q B6 6 68 8476 (odd part #, isn't it?) in the EPC for 87+ 560SEL.

Do you know if one will fit an 87 300 SDL? Can you point me toward the write-up (thread) on the mb coupes site.

I would really like you to post the pictures of the mods you have done on here if you can.

It will be very helpful, since I hate having to ahve the Window open in the summer all the time. It gets to hot....

and will any R4 compressor work out? Can you tell me where I can buy some of those parts etc.... thanks

parallel flow condensor (15.5X24.75), all kinds of beadlock fittings and hose and great help available at ACSource.com and ACKits.com. Check the links section on this site: http://www.aircondition.com/

nhodges: The electric sunshade should be a direct fit to your car. If you remove the parcel shelf you'll see pre-perforations on the underside of the shelf for the shade and motor. It should be a drop in (assuming MB didn't bother to have different parcel shelf dies on the assy line, and I can see no reason that they would).

There are searchable archives here: http://www.mercedes.cx/560SEC/archives/

I believe it was a poster nemed "Talbir" or something like that, and it was within the last year, probably even more recent.

Edit: the posts are under "sharan bains" (also known as Talbir)

thanks once again...

jbaj007

Just installed the R134a in the 300TD. Parallel flow condensor, 14X22.5.

http://www.peachparts.com/shopforum/tech-help/81979-parallel-flow-condensor-installed-w123.html?highlight=parallel+flow+condensor+dave

All parts of AC system new. Evaporator was leaking which started all this. Had about 50% blockage of air flow on the evaporator.
Here's the link to that post

http://www.peachparts.com/shopforum/tech-help/74964-evaporator-out-300td.html?highlight=evaporator

Heres the question. How much freon did your system take. Mine calls for 42 oz and the normal 80% of R134 for a R12 system should have it take 34 oz or so. It's taking about 30 oz. With that amount the vents are 35 degrees (outside 72) with the Aux fan on and an extra fan blowing on it. Did you find your setup took less?

Also. My pressures are running low. The manual calls for 22psi low and 265 high. I'm running 17 and 185. But the vents are 35 degrees. What are you running?

For everyone. I'll post the results of the parallel flow conversion with R134a as the summer progresses. I will try to set up a meeting with Larry Bible and do a side by side comparison. If the R12 is better I'll convert and we will have info on the parallel flow with R12.

Dave

Thanks for all the info jbaj007! This topic seems to be a popular one here, so it makes sense (if you don't mind) to keep questions and advice in this thread so that everyone can read it :-). Bear in mind I have no experience whatsoever with AC so some of my questions may be a little basic (thanks again for helping and feel free not to answer if I'm asking too much!).

How did you get the custom hoses done? This seems to be the most troublesome part of adding a parallel flow condensor. If an AC shop did it for you, how much did it cost? How did you know what fittings/adapters you needed?


I plan on installing an electric main fan (variable speed depending on temp.) and may replace the auxiliary one if you think it is necessary. How much better is the fan you got compared to the stock one?

Did you have to take the dash out for this?

How cheap was "cheap"? my current compressor seems to work fine, do I need a new one? Will any R4 compressor fit into our cars, or do these things come in different shapes and sizes? Any recommendations?


Got that on my list too. Have you looked into the laws about tinting the front windows here in CA? I've heard different things, from "you can't at all" to "up to 88% is legal" to "as long as they aren't too dark you won't get a ticket for it anyway" ;-).

The compressor you need is an R4 "Light" made by Delphi, metric fittings. Its $225 brand new from ackits.com. I just ordered one today. If your R4 compressor is working AND does not leak, you can use the existing one.

Some of the comments made by Dmorrison bring us to this point: how do you know the system is still properly charged (dude, you are in Santa Barbara, it aint that hot there)? Seriously I know you have a wagon, and the load is higher than on a sedan.

You may have a leak. R134 needs to be properly filled to capacity. Its not nearly as forgiving as R12.

You've got a 20 year old car, you said it was converted BUT was this the only work that was done on the system? After pulling apart my 20 year 300D on Sunday, the O-rings are all dried up, the pressure switch was leaking, the front shaft seal was leaking a little. A couple of the hoses had bulges.

Any time it gets into the 90's :eek: I have to consider it pretty hot. Hell, it's midnight and it's still nearly 90 degrees in my house. Forget the car, I want AC in here :rolleyes:.

Thanks for the info. I am going to stop by my mechanic tomorrow anyway, but as far as I know everything is running as well as it can. I guess we'll see....

81Wagon,
Don't even consider messing with the internal setting on the TXvalve.... they are about $25 new.....and remember he is testing a different refrigerant right now....just get a new one...and be sure it is the one for R12..... it takes specialized equipment to properly reset it .... and you don't have it....
Keep reading the archives on AC info..... someone told all about the P flow retrofit and told exactly the sizes of the custom fittings he had made....they are there somewhere....may have been GregS...

DMorrison,
when you said " Evaporator was leaking which started all this. Had about 50% blockage of air flow on the evaporator.
" did you mean you had blockage on the condensor ? (the one at the front of the car )....

On your pressures..... You may need to wait until it is hotter to determine if you have installed the correct amount of refrigerant...pressures are closely related to load... so at 72 ambient those figures may be ok...or at least may not be able to spot a problem without higher outside temps (load)...

1.)custom hoses. You must prefit them before crimping. Get your beadlock fittings in hand (ACSource) and there are some unusual ones you'll need; never did find a #8 female to #10 hose w/ a 90º bend and a port (R-12). Strip the ferrule from the manifold hose you'll be changing (discharge). Trim and dry fit the new hose and mark it with paint to preserve orientation. Take it to a good A/C shop and have it crimped.

2.)All my fans are original. I just relayed into the pressure switch on the R/D so the aux. fan will come on when the compressor engages. Also installed a "street rod" thermal switch into the thermostat housing (drilled and tapped) to turn on aux. when coolant temp. goes up a little more than 90+º (it's adjustable) when A/C not engaged. (overkill).
The viscous fan is subject to great variations in when main fan engagement occurs, even though commonly used. I refurbed my viscous fan clutch with some silicone oil from Toyota (6000cst) and very slightly shortened the pin under the bimetal strip for earlier lock-up.

3.) the evap temp sensor is next to the TXV(expansion valve) and determines the minimum temp for the evap to prevent freeze-up. There is a small screw that can be adjusted once it's out. MB says not to. Minor difference of opinion. The driver's kick panel and carpeted console panel on that side must come out to get to it but that's about all. Just go next to the expansion valve and you're there.

4.)R4 compressor was a "steal" on ebay. A guy had bought it and couldn't use it on his Suburban or some such.(less than $100).

With a modified system and a "test" refrigerant in, I charge by pressures. I like the old standby:1500-2000rpm... high= ~2.2-2.4 X ambientºF/ ~25-30 psi on the low; checking vent temp as I go.

This is what I've done, not what I'm telling anyone else to do. Please don't discuss "alternative" or "test" refrigerants with me or whether MB did it one way and it can never be improved on. This is only one way to handle improved cooling for those who want more. (yeah, I know they sold a lot of 126's in Saudi) ;).

Currently you can hang meat in my car. ;) ;)

Bruce 1984 300SD

Not to hi-jack your post, but I got mine back together tonight. She's blowing cold (at least it feels cold now, we'll see the weather heats up). Not sure its perfect, I didn't like the temp reading at the vent at around 50 degrees while engine was running (aux fan NOT running) and car parked. Filled with R12, approx correct amount of 2.9 lbs. 30# jug is hard to gauge without a low weight scale. (My buddy was using a digital floor scale that required over 50 lbs. to trigger the meter.)

Outside temp was 65 degrees at almost sea level. Pulled vacuum for 30 minutes. Checked for leaks. Highest vacuum we were able to pull using a brand new Robinair was 25. Maybe the gauge is off?

Low side 30 lbs. Hi-side 150 lbs.

I really need to put a pencil temp gauge to it while driving to see if its doing its job.

Any thoughts?

If you later (when weather gets warmer) run into problems which you can't figure out the cause for... you may need to take out the R12 and find a way to accurately measure it..
ANY OVERFILLING of refrigerant REALLY degrades the ability of the AC to do its job...

No not the condensor, the evaporator. After 22 years of west Texas dust coming into the metroplex the evaporator was traping alot of dust and debris. And the Evaporator was leaking. Dealer verified it and I put a electronic sniffer in the vents with the appropriate "beeps". Here the picture of the evaporator.

Dave,

Do you think its possible to invent or make some sort of contraption that can clean out the dust and debris and flush it down the evaporator drain line WITHOUT taking apart the entire box?

Something like a plumber might use to "see" inside pipes. (those systems are $10,000 btw).

Seems like most cars after 20 years will have some sort of blockage in the evaporator.

Those fins look awfully tight in there.

Cool picture, Dave. When I changed the evap in my '87 wagon late last year, it was about equally cruddy. Different shape in the 124 car, but still a mess. I'm convinced a good part of the deteriorated a/c performance in these old cars is just that the heat exchanger surfaces are covered with dust and junk.

Reading back to your charging pressures post, I think you're likely a bit undercharged. I might expect the high side to be a bit lower with the parallel flow condenser, but the low side is still too low. You might have freeze-up problems with the evaporator unless you get the low up above 20. Remember, evaporator temperature is directly related to low side pressue.

My $.02

- JimY

"evaporator temperature is directly related to low side pressue. "

I am not sure in what sense you meant that.... but what used to be called the " suction throttling valve" which is in the ' block valve' combined with the Expansion valve in most of our cars should be affecting much of the temp situation... with the evap sensor not letting it get below 32 at the evap fins...

Oh Great ,Dave ,,,, now you have me worried that I need to take my 240 evap box apart and clean it... it spent most of its time in Arlington.... yours was really dirty.... can't afford that much blockage here in Texas....

Dave, did you do it yourself... if so how many hours did it take ?

"evaporator temperature is directly related to low side pressue. "

Pretty straightforward, really. The lower the low side pressure, the lower the temperature of the boiling refrigerant inside the evaporator. Check your guage set. The low side guage will have several sets of numbers in addition to PSI. There will be markings for R-12 and/or R-134 and/or R-22. Basically, these are the refrigerant temperature for the respective refrigerant at that pressure. R-12 and R-134 pretty much align one-to-one with the pressure, i.e. 40PSI is quite close to 40 degrees. R-22 is much higher pressure refrigerant, I think it runs about 65PSI at 40 degrees.

On your home a/c, do you know what is a common cause of the evaporator icing up? A refrigerant leak causing an undercharge!

Back to cars, why does this matter? Because if your low side is 17PSI, the expansion valve is wide open, doing its darndest to feed more liquid refrigerant into the evaporator to raise the pressure up to ~30PSI. This is probably what Dave had happening in his modded 123 system.

OK, thought number two. On my 124 (at least) the evap temp sensor measures the temperature of the airflow coming off the evaporator, not the temperature of the evaporator itself. Subtle difference. With the right combination of low side pressure, outside air temperature and humidity, it might be possible to ice the evaporator without triggering the evap temp sensor shutoff. Remember that an undercharge lowers the low side pressure (and hence the temperature of the boiling refrigerant inside the evap) while also reducing the number of BTUs which are removed from the airflow stream passing over the evaporator. Get everything just right and you might ice the evap without doing enough cooling to trigger the evap temp sensor shutoff. I think we had a member do that with their 129 the other week - they had an operable system, but were only about half charged.

BTW, I'm not a refrigeration engineer, I just read too much. And I'm probably wrong anyways... My $.02.

- JimY

"evaporator temperature is directly related to low side pressue."

I am still not buying this... but am having a problem putting into words the reason for it....

When you say ' ice the evap' .... you mean on the outside where the air is flowing ( with the moisture)... right?

The evap can only ice internally if it has moisture in the system...

According to your logic it would be best to underfill a system in order to get colder air.... but underfilling takes away total capacity and makes the compressor work much harder... so it would be temporary at most...

That thermo syphon valve in our block valves should try to keep the system from going below 32 by itself... then if the temp does go there the other sensor is supposed to cut off the compressor...on our systems... which is the cycling compressor type... later cars mostly went the other one which keeps the compressor on all the time... and deals with the differential pressures with that tube mechanism...

Our block TX valves are barometric pressure compensating....

I think that pressure differential may be more important than low side pressure per se....

.... the major evidence being that ANY overfilling of the system really starts degrading the systems ability to cool fast....you must be able to produce a significant difference for the change from high pressure liquid to low pressure vapor to cool an autombile ... given the high load it represents....

Ok,, still trying here..... that statement may be true in and of itself... but does not apply to the dynamic of getting an AC working all the time in an automobile...IE, you need the prescribed amount of the correct, clean refrigerant in the system to expect it to do its job and last the time it should...

I'm definately talking about icing the outside of the evaporator. We'll assume the system is free of moisture in the refrigerant.

Here's a reference to a website that perhaps explains things better: http://www.bennettauto.com/air_conditioning.html

Try typing something along the lines of "evaporator freeze up" into Google and see what comes back.

Lastly, I refer you to all the myriad refrigerant temperature/pressure charts out there. Here's one: http://www.aircondition.com/pressure.htm At a given pressure, the temperature of the boiling refrigerant is certain to be equal to the value given in the chart. For example, at 17PSI on the low side, the temperature of Dave's boiling R-134a refrigerant was between 15 and 20 degrees Farenheit.

As far as how we know the exact temperature of the boiling refrigerant at a given pressure, I refer you to the empirical gas laws, passably described here: http://www.psigate.ac.uk/newsite/reference/plambeck/chem2/p01042.htm

I took AP chem and physics in high school 20+ years ago, finally found a use for all that geeky stuff...

- JimY

jbaj007,

you wrote:
<<Take it to a good A/C shop and have it crimped.>>

I live in Mar vista which borders Santa Monica to the south. Could you tell me name and location of a "good A/C shop" for rebuilding A/C hoses?

Thanks

You don't want to know. But Iv'e become very lazy since my daughter went to college and were empty nesters.
Im goin to say about 4 good days of work. If you want I can guide you. I did post the reassemblly of the dash when I installed the evaporator box. Do a search it might cut off some time for you. I had to "go back" a couple of times when I realized certian things were not done in the correct order.
The car has spent its life in Oklamoha and Texas. It's got to be Oklahoma's fault :D :D
If your doing it, replace everything. Evaporator, vacuum elements, Foam, rubber connectors to the elementsand clean the entire box. I did not replace the heater core, I hope I wonn't be sorry later, but It just did not seem to fail.
I have a CD of all the steps to the job in pictures, except the box rebuild and removal. I can make a copy for you if you want.

I do wonder if a vacuum attachment down the center vents might help a little. A small hose like used to clean computer keyboards. That might get the majority of the dust.
Or you can remove the dash, which is not a terribly big job and clean it installed in the car. That way you can do the elements and check everything over. Here is the unit in the car.

Dave


PS I now have a leak in the condensor R/D fitting. Glad I used R134a and not the R12 first. At least I hope it's fitting and not the manifold welds. I'll find out next weekend. Going on a cruise this week.

erubin,
Santa Monica Radiator & Air Conditioning at 1537 Lincoln in Santa Monica.

Owned by the same family (the Perletter's) for 80 years.

Small shop with nice people; have always done right by me; hope the same for you. Take care, Bruce.

Really had to "dry fit" mine alot before I crimped and I still had forgotten (duh) the high side fitting. Luckily, adding it later made up for a short hose (my fault). Fit, fit, fit, fit again....then crimp.;)

jcyuhn, The reference sites you posted really helped me get a handle on my objections to the original implication....

Remember that the Bennet site is making some generalizations when describing ac systems in order to cover many types...

The important section with regard to what we are discussing is the ' control systems' segment....

I believe you have taken some statements like " in many systems" and " most"... and extrapolated one of the statements in the opposite direction..... without taking into account the dynamics of the situation...

My first example of the logic here is this...

When you walk up to your car with it not running... you start the engine in order to start the compressor and produce cool air. Does it then make sense that when it has become too cold that you would cycle the compressor ON in order to reduce the temperature in the evaporator ? I say no...

Your temp/pressure charts are not applicable to the analysis of the dynamics of the overall system.

The last paragraph under ' system controls' is the important one... but it says it in a way which implies that ' cycling compressor and fixed orifice' have to be paired... not the case in our cars... we have a cycling compressor with an TX valve... and it is the dynamics in that block valve which are supposed to be controlling the temperature of the evaporator... when the temperature in the evaporator gets too cold the valve closes in order to spray less refrigerant into that space... thus lowering the outside temp of the evaporator...

at least this is what I dreamed last night.... LOL

and one last shot at the logic.... according to your charts... the refrigerant will have to be reduced to a certain temperature in the condensor in order to switch to a liquid .... in order for the liquid to be sprayed into the evaporator... and get the ' phase change ' effect upon which this entire operation is based... so how would this ' raising the temp by turning on the compressor' work enough on the OTHER side of the condensor to affect the control of the evaporator temperature ?... bottom line is it won't... the valve at the entrance and exit of the evaporator is supposed to take care of that...

Dave, Wow ... four days... that was about my impression from others posts.... but WOW anyway....
I do not think a vacuum down the vents is going to help because that mess was on the other side of the fins from the vents...but I do think a pressure wash from the vent side through the fins might be helpful...
I just think I am too old to pull the dash... not into that kind of detail right now... LOL

Let's not forget my classic post:

http://www.peachparts.com/shopforum/tech-help/41181-vent-temps-r-134a-w123.html?highlight=134a

I could be wrong, but I think I was the first on this board to do the parallel flow conversion in a w123. I'm going on my 3rd summer after the conversion and it still works great. One thing I always mention is that my auxillary fan is almost always on when I'm idling in traffic, so I wouldn't waste a bunch of time with rewiring the fan or whatever to get it to go on. Just replace the pressure switch with a new one designed for 134a and it will come on more often than you think it will.

Good luck,

GregS
'84 300D, 183k
'90 300CE, 174k

Greg,

I hope you meant the temperature switch and not the pressure switch.

Edit?

Eric

I've spent a couple days thinking about parallel flow condensers and this is what I've come up with...

I plan to use this condenser from ACSource.com (it should just barely fit; if not, only a tiny bit of cutting should be required).

Because the fittings are on opposite sides, and because my compressor to condensor hose seems to be on its way out anyway, I plan on having a new section of hose fabricated to come through the driver's side to the compressor (it'll still have to hook up with part of the old stock hose - I'll have that shortened with new fitting crimped on - because I don't think I want to mess with that weird double-hose fitting on the compressor itself).

Here's a quick before-and-after diagram I made up; does anyone see anything stupid/wrong I may have done? Any advice? Does it look like it'll work?

http://www.moesaverage.com/AC-upgrade.jpg

Diagram looks doable. Make sure a HP fitting for your quages is put on the red hose. What about your washer tank? Will the hose go under the sheetmetal or under the tank? You will have to make a hose for the passenger side fitting to the R/D. Getting the hose to bend is not easy. Getting the correct fittings welded together is how I solved it. Or you can cut the sheetmetal near the fitting and make a hose to the R/D. This is why I made the "manifold". 2 fittings per opening and some tubing TIG welding together. I am using stock hoses in the rest of the setup.
The purple hose is the manifold hose. Very expensive and would be a pain to reconfigure. I would suggest making your hoses to fit the manifold hard metal section. Otherwise fitting hoses to the compressor will be a hit and miss setup. Make sure you give the hoses support so you don't wigggle the fitting loose over time.
Metal hoses from the condensor to the R/D. I would suggest putting a rubber hose section in there. The vibration of the car could cause the metal hose to crack over time. The rubber section would absorbe the vibration.
Dave

Leatherman -

I'm not really much into debate, so let's just drop it. I'm comfortable with my understanding of a/c operational theory, I think you are too. We just don't happen to agree.

So I'll toss out one last comment, then I'm bowing out of this thread - there are already too many conversations going on in it! In your last statement you imply there is valving on both the inlet and outlet side of the expansion valve. That is incorrect - only the inlet side has any restriction. It contains a needle valve to meter refrigerant into the evaporator. The low pressure side of the valve is wide open; the entire evaporator is directly connected to the suction side of the compressor with nothing between it. So there is metering of refrigerant into the evap, but not out of the evap.

- JimY

Thanks for the reminder about the high pressure fitting; I've added it to my diagram so I won't forget :-). The hose should be able to fit under the washer tank; the tank hangs a couple inches above the sheet metal in that corner

I guess that part of my diagram wasn't entirely clear. The only parts that will be metal will be the same as your "manifold"... Just the part that comes out from the condenser to meet up with the stock hose to the R/D. Here's a new diagram of that specifically (hope you don't mind I used your very own "manifold" to make it up in photoshop ;) ).

http://www.moesaverage.com/condenser.jpg


I don't understand you here. Do you mean hook my new HP hose directly to the manifold hose metal lines? I don't think it is possible. The $*&#@ thing is one solid piece, including the hose that comes off it:
http://www.germanstar.net/Pics/0001300557.jpg

I was thinking of cutting that hose in the middle and crimping on a new fitting and connecting that to the new HP hose (hopefully the hose is flexible enough to double back on itself). Hmm, though looking at it now it seems maybe I could just unbolt the other metal end from the oil pan (passenger side of car) and mount it somewhere on the driver's side instead; then I could hook the new HP hose directly to that.

The hose would still have to double back on itself though... I wish I could just hook the hoses directly to the compressor and forget that ugly manifold fitting altogether. Could I cut the manifold hose at the metal line and have a new fitting welded to that?

"hopefully the hose is flexible enough to double back on itself). "

You really need to do what ever is necessary to avoid this... even if it worked initially... chance are that at some point, either from vibration or age it is going to cause a restriction to your flow... a metal u pipe , even at the expense of the more fittings or joints will be worth the peace of mind in longivity and performance... that is one of those hidden things which 5 years from now would be hard to diagnose...

And of course the obvious evidence of this prudence is the lack of such items in the original car... if they needed a 90 degree bend in rubber then it was cast that way ( radiator hoses) ... not taking a generic straight hose and putting it into a relative sharp bend... and never into a hairpin turn...

Okay, thanks. I'll try to find some better way of modifying that ugly manifold hose line to connect on the driver's side. Hmmmm...

Isn't there a parallel flow condensor with both ends coming out of one side. That would seem to be soooooooooo much easier.

Eric,
Most/many do. http://www.acsource.com/index.asp?PageAction=VIEWCATS&Category=254

Well then, with all due respect to 81wagon, why is he adding complexity to the project AND using a parallel flow condensor that requires the plumbing job from he**.

I don't think you need to modify the manifold hose if you use a parallel flow unit with both ends on the passenger side?

Whats your thinking process on this?

Yes, but they're all smaller... The stock condenser is almost 17 inches tall and I was hoping to put in a parallel flow condenser that would actually fill up the available space (as opposed to a 14 inch tall one). The increase in surface area from the one dmorrison used and the one I hope to use is about 20%... I just figure more couldn't hurt :-).

Particularly when my compressor-to-condensor hose on the passenger side needs replacing anyway - might as well fabricate a new one that will fit on the driver's side instead... The only extra work that will be required with this over a smaller one with both fittings on the same side is 1) Drill a hole (no problem) and 2) modify the manifold hose line from the condenser to point to the driver's instead of passenger's side (hopefully doable!).

Yes, you would not want to lose the extra efficiency you get from the P condensor by using a smaller one than you can manage to fit in there.... Just keep in mind fluid dynamics when designing it...

After lots and lots of reading up on this when considering how to maximize my 240 AC... I found that this is THE RULE :

The Primary limiting factor in any ac design is AIRFLOW ACROSS THE CONDENSOR..... which is some coefficient of air heat transfer times the efficiency of your heat exchanger....etc...

So this is where you have to be sure you are maximized if you are to hope to realize any other improvements you have done to your system...

81Wagon,

I'm posting this for those reading that aren't quite up to the layout of the a/c on the 12 chassis.

The discharge hose (your description: compressor to condensor) is actually 2 pieces. A rather expensive hose/pipe assembly known as the manifold hose that retails for $450! and a shorter hose that is about $37 from the dealer.

Its a pretty wacky curve combination coming OUT of the compressor with that manifold pipe.

I now understand what you are trying to accomplish.

Take lots of pictures and when you are done we are all going to hit you up for a "kit".

Think this will help bring the vent temp down in 90 degree heat sitting at a traffic light? Lets hope.

So far so good. I've gotten my old condenser out, and the new one got here yesterday. Here they are side by side... The new one is slightly taller (half inch or so) and the width is essentially the same. It's slightly thinner. Today or tomorrow I'll get it mounted on the car and figure out the exact dimensions of the lines I need to have made, so I can take it to a local AC or hydraulics shop and have them whip it up for me..

What size is that condensor (parallel flow)? I am looking into doing the same thing. Thanks Steve

OOPS....
on page one he said " I plan to use this condenser from ACSource.com "

which was this site :
http://www.acsource.com/index.asp?PageAction=VIEWPROD&ProdID=133

A few notes for those retrofitting and otherwise altering a/c systems.

There is a direct relationship between gauge readings, elevation, and ambient temp.-refer to the standard charts.

Depending on the system, pressures are to be checked at 1500-2500 rpm

High side pressure is typically higher after convertion to 134-a.

ALWAYS install a pressure switch on the high-side line that will shut off the comp. at extreme pressure.

jcyuhn knows more about the functioning of these systems than what you give him credit for. Low refer. charge can definately cause evap and line freezing(note that if you have internal line freezing, you have other issues-though I believe this to be nearly impossible)

parallel condensors are slightly more efficient and were primarily developed to overcome the high side pressure increase (compared to r-12) of the 134-a. Some makes simply must have one in the conversion process, M-B is not one.

When replacing hoses, use barrier-type hoses.

Change the oil in your compressor when servicing and use the proper oil for your refri.

Upgrade to the blue and green "o" rings.

If your drier/accumulator is more than three years old-replace it with one containing the best dessicant possible.
If the system is open more than a couple of hours and the drier is not new, replace it. If you had any restrictions in your system or compressor damage-replace the drier.

Spend the money on a known brand of compressor- especially the r-4. The r-4 is not a well made unit to begin with, skip the cheappy rebuilds.

I finally waded through this thread and will be installing a p flow condenser in a 300SD and plan on keeping the r12 refrigerant. I got the condenser from Plantman and it looks like it should fit like a glove with just some modifications to the hose ends which I will get the local hose house (Tubes N Hoses) to help with. I'll keep ya'll posted.