How does one increase reserve capacity ?
Would putting two reciever/dryers ( in parallel ) help ?
Would putting a new condensor of the new parallel design help ?
Parallel is my new favorite word.

Anyone have hands on experience with one of the new parallel condensors ?

The only way to acheive better cooling (and I'm assuming you are talking about a 134a conversion on a w123 or w126), is to swap in a parallel flow condensor. Install the biggest one you can fit. The bigger the better. Two driers wouldn't do anything.

Read this for my experience:
http://www.peachparts.com/shopforum/showthread.php?threadid=41181&highlight=134a

GregS
'84 300D, 174k
'90 300CE, 164k

Yup, I remember that thread. Still haven't done the total a/c changeout on my 124 wagon; wish I had that kind of time to tinker.

While a parallel condensor is a big step forward, there is still one problem area on many older mercedes. Depending on the compressor used, there is simply no way to get really cold air at idle. This particularly seems to be a problem in cars which use the Nippondenso 10P15C compressor. It just doesn't "put out" enough at idle to adequately cool the air. Simply put, the amount of liquid refrigerant delivered to the evaporator isn't sufficient to fully cool the airflow.

I think dual receiver/dryers would be an interesting trick. I would not expect such a setup to deliver any cooler temperatures driving down the road. However, they might help with idle performance. The R/D is also a fluid reservoir - it stores liquid refrigerant until called for by the expansion valve. Adding a second R/D would essentially double the quantity of stored liquid refrigerant. I expect the vent temps would stay cold for a longer time at idle - until the contents of both R/Ds were exhausted.

- JimY

Actually I am only shooting for MAX R12 capability.... I have my system apart.. thus would not want to miss an opportunity to upgrade... I am in a HOT and HUMID area... my motto is " you can't get the inside of my car too cold ".....
The newer condensers are not expensive.... less than $100 for the one which will fit my 240....

Jim, that was my feelings on doubling the Reciever/dryers...more total CC's inside the system... not colder.. but more RESERVE before not blowing cold...

Maybe your car needs a larger ( 10 percent ? 15 percent?) crank ac pully circumference... so that it does not disappoint at an idle...
Don't know how hard that would be to find or make.... but seems the direct fix..... on the other side of the equation... it might cause the compressor to average less time on... but cycle more often... but not enough to matter with regards to clutch wear .(IMO)....

I have no personal experience with the pareallel flow, but I have read several stories regarding their increased efficiency.

I think the cold air at idle problem was directed toward a system converted to 134. I think the parallel flow would help but we have no way of confirming until we have a guinea pig. It sounds like your willing to offer yourself and your 123 up as the guinea pig.

If you follow through with this, please let us know exactly which size condensor you used and your results.

I'm sure you're aware that you'll have to make two new hoses. This shouldn't be too big of a deal. I expect to get a hose crimper before too long. I am starting to collect some more equipment for a/c work with the idea of doing it professionally in mind.

I pick up my recovery/recycle machine today, then I will get a refrigerant identifier, sealant identifier, and then a 134 recovery machine. There is a hose crimper for about $200 that looks like it will work well with a vise.

Sorry to ramble. Please keep us posted on the project.

BTW, I agree that I don't think an extra receiver will do much, but it would be just one more place to ensure condensation. Remember having more refrigerant in the system won't gain anything, it's having more thermal capacity for condensation that will result in more cooling capacity.

Good luck,

WOW , Larry, I did not know you were planning on getting all that good equipment.... You ARE my new BEST FRIEND
Yes , I am planning on keeping exact notes and taking the best pictures I can..... there are lots of 240s' out there... I think many people will benefit from upgrade info....
So I can just send my hose ends to YOU.... ? with specs on how long I need them ?

They make valves for some of these things... and I was thinking about installing Isolating valves on each end of my Reciever/dryer when I put it in.... if I did that on two parrellel Reciever /dryers I could alternate changing them out once a year on principle... cheap insurance to fight moisture...

I was talking about this subject on the "other" site while discussing the merits and drawbacks of converting the a/c on a Ford pickup to R-134, and the best suggestion I heard was to put a second condenser in, if it could feasibly be plumbed into the first. I asked if there could be any problems besides dealing with the connections, and the reply I got was that the only problem I'd have would be scraping ice off of the inside of the windshield.

I haven't tried it yet, but have been thinking about doing so on both vehicles (the 300D was converted before I bought it; the truck still needs to be converted)...

One other thing I thought about (haven't done this yet) is to put some insulating foam over the low-pressure side...on my car, a lot of that's bare metal and we could be losing some efficiency due to that line being heated up by being in the engine compartment...

Just some thoughts

__________________
2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999

leathermang,

I will be happy to make hoses for you once I get the crimper. Before I get a crimper I will get the other recovery/recycle machine and an identifier. The crimper will be last.

The way things are at the company I work for I may be doing this for a living sooner than I really want to.

Have a great day,

One cheap, relatively easy retrofit that would nicely complement a parallel flow condensor would be a heavy duty electric fan setup. As Larry said, low speed cooling problems are related to not having enough refrigerant, which is caused by a lack of airflow through the condensor at low speeds. One way to combat this is a serious electric pusher fan, or even two. I'm thinking of my old Saab 900 that had a dual fan setup where both would run when the a/c was on. I don't know how efficient the stock w123 fan is, it doesn't seem all that bad, but fitting the largest, fastest electric fan, or some dual fan setup, would probably be even more efficient. And then hook it up so you can turn it on manually if necessary.

Its hot here in DC in the summer, and I find that my electric fan will run almost all the time in traffic, but I don't get really great cooling if I'm stuck in traffic. But remember, I have r-134a in my car, so my vent temps are really good, and I attribute that all to the parallel flow condensor.

The electric cooling fan, and sticking with r12, are the only two things I would have done differently if I had to do it all over again.

GregS
'84 300D, 174k
'90 300CE, 164k

Where can you find a dual fan setup? I'm interested in this, double 'cause my stock fan is dead right now.

Also, what exactly is a parallel-flow condenser? Would that have a smiliar effect to the dual condensers I mentioned earlier? Also, where can those be found?

Hmm...might make it worthwhile to tear into my a/c system, even though I've already got R-134...

condensers...

http://www.ackits.com/index.cfm?fuseaction=Parallel

high perf fans

http://www.ackits.com/index.cfm?fuseaction=Electric

haven't seen the dual fans...

More capacity requires moving more refrigerant through a larger evaporator. This requires a larger condensor, too.....

Storing liquid freon in a second reciever/dryer will only help until it blows through -- the real limitation is the capacity of the compressor at idle -- it only moves what it is designed to do. Smaller pulley will help (it runs faster), but you risk overspeeding it on the highway.

The old York or Delco systems were better in this reguard -- they ate horsepower terribly, but since the were designed to have huge capacity and only operate intermitantly, they will keep you cool in hotter conditions. Hard on the cooling system though, and will blow the high pressure hose if the aux fan doesn't run (I know, I did).

Be carefull not to overcharge with 134a -- it requires lower pressure on the low side to cool properly, and make sure if you are using the temperature scale on the guage set that it is for 134a and not R12 -- temp and pressure are the same for R12 in the evaporator, and you never want to go below 32 psi with the expansion valve open (to prevent freezing). 134a need to be mroe like 28 psi. Note that when the expansion valve closes (if you have one), the pressure can drop to zero.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I am sticking with R-12 myself.

Could the time it takes to ' blow through'... increase the time in traffic on a hot day before the system starts to not cool the way it should ?

That is all I assumed for the doubling of the R/D ..... and perhaps the ability to change it out for moisture control without evacuating the system... ( with proper isolating valves )....

OK, I have the Delco R-4... so I am in better shape on this than a nippond compressor would be ?

Seems to me logically that the condenser is much more a bottleneck for efficiency or capacity than the evaporator... thus the quick reaction to an aux fan not working...

So I am going to put a parallel condenser in mine without changing the evaporator... which I would not have a clue how to manage in such a tight space anyway...

Does a non-op aux fan only affect the a/c output at slow speeds, or can a dead fan affect the output on the freeway as well?

I've heard that some electric fans can actually be counterproductive at freeway speeds; they can't keep up with the natural airflow and can actually make less air go into the condenser/radiator...I don't know if that may or may not be the case here, though.

Of course, I need to replace my engine fan clutch as well...

Also, on the parallel-flow condenser, I couldn't readily see what the difference was between that and the serpentine condensers...?

Warden,
The parallel flow condensers may not look any different than a transmission oil cooler, although I have no experience with them, but my guess is that they have been R&D'd to be more effecient and meet the requirments of making 134 suitable to use.

it appears that the overall dynamic's of using 134 prompted the need for some changes in any 134a application, be it a desktop refrigerator or auto ac.

Leatherman....
great idea, on isolating R/D's with valves.(long as you can get some good valves that will not leak.

you would still need to evacuate the R/D canister & hoses since they are full of regular air. right?
if so then you'd need to throw a valve in per canister.

(my understanding is) The accumulator/orifice type system is less complex than expansion valve type, and I do believe it uses some type of desicant bag for isolating impurities, however, I've just got to believe, engineers would have stuck an accumulator type resivoir on the R/D system had it been feasible.

Look, if you really want your condenser coil to work effeciently, then forget about any high velocity electric fans.
What you do is reroute the condensing coil to a Coleman cooler in the trunk. Fill it with ice every day before you leave the house.

Now, if you are going to have your hoses "re-hosed"... would you use the "barrier" type hose?
I ask be cause maybe you may want to go to 134 someday, (you know if you get too cold while idling in traffic with R-12)
www.centuryautoair.com (Tucson, Az) quoted me around $40 per hose. I thought that was reasonable, however, 82 240 has 4 gas hoses plus the liquid line!

I am very interested in your "parallel" condenser upgrade with the R-12 application. This system will be so efficient You may not need an AUX fan at all!

How old is your R-4? still healthy?

Keep us posted.
dave.