1982 300TD R134a conversion with parallel flow condensor update!! - PeachParts Mercedes-Benz Forum

dmorrison · #1 07-20-2004, 06:20 PM

Want to keep everyone updated on the R134a conversion I did in my 1982 300TD. This update is provided by the 100 degree day we experienced here in the DFW area

This was the "conversion" which consisted of a complete rebuild of the AC system. All new components-- Compressor, evaporator, hoses, orings, expansion valve, paralell flow condensor, R134a and synthetic oil ( good for R12 and R134a)

The posts.

The plan and comments.

Review of my plans for the AC system, comments welcome

Parallel flow condensor

parallel flow condensor installed in a W123

Synthetic oil and why I used it. Because the system can now go between R12 or R134a WITHOUT FLUSHING.

Ac system rebuild-- synthetic oil R12 to R134a

The new compressor vs. old
Some techs I trust said to never use a rebuilt R4 compressor. 90% of the time they fail after 1-2 years.

Installing the dash
Remember I had a leaking evaporator which started all of this.
Notice the amount of crud blocking the evaporator in the pisture about half way down. This may have a significant effect on your conversion.

Order for installing evap box in a W123.

Compressor seals and hoses.

AC rebuild one step forward-two steps back.

Sooooo hows is it going. The other day it reached 100 Degrees here in the DFW area and I will tell you that the car is very comfortable. I posted that I would like to compare it to a 123 R12 system, but Larry Bibles is not working. I got my daughters 240D system working. Its R12. was low on R12 and after adding a can I could not find a leak with my sniffer anywhere in the system. I spent 2 hours searching and no leak. I have added dye with the last can added to bring the pressures up to normal operating limits and so far no dye in the evaporator drip

So to compare the 2 lets discuss the differences. The 240D has no tinting. I run R12 in a standard system with pressures of 22 low and 265 high. The 82 300TD has R134a. A NEW evaporator as well as everything else. tinting, legal tinting, and a parallel flow condensor. R134a and the aux fan is on all the time. I'll try the system with it in the normal mode.
I think the 240D r12 system cools just a little better, may 5% better. My temperature guage for the vents, I think is wrong. But by driving both cars I think the rebuild to R134a is a success.

BUT here are the caviots.(sp)

I have a NEW evaporator, The blockage of the old one was significant. What is the blockage on the 240D, I do not know. Air movement is good, as good as the 300TD? It seem so. What is your cars evaporator like, That may be a consideration. I wish there was a way of checking them without a boroscope or taking out the dash.

So the conclusion, Go with a parallel flow condensor if you are thinking of a R134a conversion. I will get a new thermometer and post the 240D and 300TD temps.
Use synthetic oil after the flush. If you are not happy with the R134a then converting back to R12 only requires an evacuation and recahrge. No flushing.

I hope we can get someone to post who has done the conversion WITHOUT the parallel flow condensor.

Yes I am very happy with the vent temps, Idle speed temps and the results I have gotten. All comparing it to the 240D With R12.

Dave
7709

Let the posting begin.

whunter · #2 07-20-2004, 08:24 PM

Hmmm.
It would not shock me to find automotive climate control engineers following this thread.
This is a great subject with tons of food for thought.

leathermang · #3 07-20-2004, 08:30 PM

Dave, You are one ORGANIZED man. Great info......

R Leo · #4 07-21-2004, 09:46 AM

Dave,
What a great thread! It's good to see all the speculation and guessing about what to do to improve the a/c systems on these cars finally turned into action and fact. Now I know what I'll be doing this winter.

Take care!

Rick Miley · #5 07-21-2004, 10:15 AM

Dave, do you plan to convert the 300 to R12 once you're sure it is leak free? That would provide another very interesting data point.

Quote:

Originally posted by leathermang
Dave, You are one ORGANIZED man. Great info......

That's the way pilots are.

Eric Eliel · #6 07-21-2004, 10:21 AM

Dave,
The other thing that you may have overlooked on your post is that the TD's interior space (wagon vs sedan) is larger than the 240. Therefore more work. AND the 134a conversion is still working pretty close to the 240's. Good job.

Your next project should be to find a used boroscope on Ebay, design an attached water jet AND then we can rent it from you to clean our evaporators.

Eric

jcyuhn · #7 07-21-2004, 10:49 AM

Dave -

Interesting timing on your post. I just changed my 124 diesel wagon from R-134a to R-12 last night.

I went through about the same process as did you. Everything got replaced - evaporator, compressor, condenser - everything. I got lazy and used a stock condenser instead of fitting a parallel flow. Perhaps as significant as all the other repairs, I replaced all the vacuum actuators. The car no longer wastes any cold air out the defroster vents, and 100% reciculate mode is definately 100% recirculate mode. Stinky cars up ahead no longer fumigate the interior of this 124.

Like you, I used a universal synthetic refrigerant oil that operates with both R-12 and R-134a. I elected to initially charge with 134 because it was so much cheaper - better to lose a $10 charge if had a problem.

Surprisingly, the 134a worked pretty well in the 124. This is a combination everybody says doesn't work, but I found it OK. It worked great all spring and into the early summer. It was adequate even on our 100 degree days. If the car had been sitting in the sun, it took about 10 minutes of stop-and-go driving to become fully comfortable inside.

I used an a/c thermometer to measure the temperature of the air discharged by the system. On the highway after dark it would put out 39 degree air, after the blower had slowed . During the day, with the fan speed up reasonably high, it would deliver 50 degree air in stop and go driving. Sitting at long traffic lights in 100 degree ambient temperatures it would creep up to 60 degrees. Accelerating away from the light it would rapidly cool down.

Now that may not sound so great, but surprisingly it kept the car comfortable. I think a lot had to do with fixing the recirculate function. When the car is not drawing in hot, humid air, the system does a better job of dehumidifying the interior of the car. Removing moisture from the air is a big part of why air conditioning makes us more comfortable. I guess very dry 50 degree air will actually do the job on a hot day.

System pressures with the 134a were OK. I charged until the low side came up to ~25PSI with the engine at 2000RPM. High side settled in at ~325PSI under those conditions - a touch higher than I like. But that's in my garage without good airflow over the condenser.

I don't have any performance figures for the R-12 yet, but will follow up when I have some data.

How come you think your temperature numbers are fouled up?

- JimY, fellow a/c hacker

leathermang · #8 07-21-2004, 05:40 PM

" Accelerating away from the light it would rapidly cool down. "
Sounds like a high performance Aux fan might help out...and it is ealy to install ....We are not into AUGUST yet.... LOL

dmorrison · #9 07-22-2004, 01:26 AM

Well let me answer all the questions and comments by "poster"

leathermang

"You are one ORGANIZED man."

With my flying yes, My garage, PLEASE don't look at it. It really is a mess. When the kids go back to college, the garage is a major reorganize project.

Rick Miley

I originally was going to put the R12 into the system once the "mods" proved reliable. But now I don't think I will. The setup has proven to be a good system and I don't think going to R12 would gain me any advantage but a $120 bill for freon. So for now it will remain a R134a system.
Now if Larry Bible wanted to lend me some R12 for a couple of hours we could run a test. Take vent temp readings. Remove the R134a and install R12 then take the same readings. Then remove the R12 and install the R134a, unless the R12 readings were much more impresive.

Eric Eliel

Yes the TD is bigger. But is it balanced due to the tinting? I don't know. But it is a factor.
Harbor Freight does have a boroscope for $169 on sale at times, a non flexable unit. Getting to the evaporator would be an absolute PITA. You would have to go thru the fan opening and get to the evaporator. I don't know if it is possible.

Its now Wednesday night, 6 hours after I started this post

I did get a new thermometer (old guage read 9 degrees higher than the new one in the vent side by side) and drove the car tonight. The first 10 minutes was hot, car was sitting in the sun. The temp would only drop to 40 driving around town. 38 on the highway. So maybe I will consider the R12. Tomorrow I will do the same with the 240D that has the R12. See how the stop and go temp readings are and then decide about the R12.

Jim

Consider hot wireing your fan so its on all the time. I disconnected the temp switch in the reciever/dryer and made a jumper for it. So the fan is on anytime the car ignition is turned on. This was I get the fan cooling the parallel flow condensor at all times.

Dave

#10 07-22-2004, 07:25 AM

whats the diff between a parallel flow condensor and a standerd condensor

leathermang · #11 07-22-2004, 10:31 AM

Dave,
I think it would be great if you can stay with the R134a.... Comfortably.....

Of the things you have changed out....the P condensor may have only offset the reduced efficiency of the R134a...

So, since we know that ' airflow across the condensor' is the primary limiting factor in ANY AC system....

Why don't you put one of the high performance Aux fans on your system before you make the decision on switching back to R12 ?
See if that makes the difference on keeping you cool with the R135a ?

dmorrison · #12 07-22-2004, 07:02 PM

leathermang

fan is hotwired so it on whenever the car is on. A high flow may improve the situation.

But here a twist to the story.

Took the 240D today. New thermometer, same one use to post the temps above.
The car vents temps ran at 42 down the highway, 40 at one point, Vs. the 40 and 38. Outside temp is about what it was yesterday driving the 300TD.

Starting the car, then ran down the road, it acted like the 300TD. Very hot until just outside the neighborhood. Cooled down nicely but as I said 42 degrees in the vents.
I will put the guages on the car, check for leaks with the sniffer and the dye light. See if the R12 is leaking which may explain the higher temp in the R12 system vs. the R134a system.

I'll post when I get it done.

Dave

Tangent, sorry

Go here to learn the difference. Basically the same size parallel flow condensor is 30-35 % for efficent so the removal of heat from the freon is better, which with a converted R12 to R134a system you need.

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

#13 07-22-2004, 07:44 PM

thank you
i love to know how thinks work

#14 07-23-2004, 09:00 AM

GREAT THREAD! And Great job on the a/c refurbs!

As I was reading through I was thinking that I needed to post and ask for vent temps and you got there.

I have never had any doubts that with enough condensor capacity that 134 would cool a 123 with no trouble. The 124 would be tougher, but can be accomplished as Jim Yuhn has shown with his project.

A big part of the evaluation is objective. And that is, different people require different levels of "cool." That's why I like to see vent temps, that takes out the objectivity.

It is guys like Dave Morrison and Jim Yuhn that take things forward. Their inquisitive and scientific nature is the necessary ingredient in finding methods of improvement. These guys have sort of a Smokey Yunich approach toward air conditioning.

BTW, I don't have non working a/c's in my 123 cars, I have non working 123 cars. If they ran, I think the a/c's would work okay. Maybe some day, I'll put the 240D back on the road.

I have done 134 conversions in the past, but I have never done a CORRECT 134 conversion. By this I do not mean that I don't flush, r/d, correct oil, evac, etc. I mean that I have never improved condensor capacity to do the conversion correctly.

I really have no problem with 134 conversion if it can get the job done. What I DO have problems with is using snake oil refrigerants.

Good job guys,
PS. Dave did you ever get the modulator working correctly on your daughters transmission? LB

jcyuhn · #15 07-23-2004, 10:28 AM

OK, first view of the R-12 performance in my 124. I've only driven it one day, so this isn't based on a lot of data. Thursday was a sunny and modestly warm day by Dallas standards, with a high temperature of 95 degrees.

The R-12 performed better during the morning commute, generating vent temperatures in the low 40s during my suburban stop-and-go commute. In comparison, R-134 would only drop to the upper 40s under the same conditions.

I ran some errands at lunch, when the temp was well into the 90s. Vent temperatures were perhaps 2-3 degrees lower than R-134 under the same conditions. I saw about 47 degrees with the blower running at a medium-high speed.

Heading home after work in mostly stopped traffic the vent temps were in the low-mid 50s - again, perhaps 2-3 degrees better than R-134.

When charging, the high side pressure was about 50PSI lower than R-134 under similar conditions.

Subjectively, the R-12 seems to cool down faster than the R-134. The air gets cold in less time. Though it does get a bit cooler, the difference isn't significant enough to notice without measurements. In both cases the car was comfortable at all times.

I don't think hard wiring the condenser fan will make any real difference. I have the newer red switch in place. The fan always comes on within a few seconds of bringing the car to a stop. It's pretty much running all the time that it will be useful.

I expect a parallel flow condenser would improve the performance of both R-12 and R-134 on the 124 chassis. However, another limiting factor is the compressor. The early 124 cars used a Nippondenso 10p15c compressor. Now, this is a nice little compressor, but the accent is on little. It has a displacement of 145cc. In contrast, the R-4 commonly used on the 123 diesels has a displacement of 176cc. In my opinion this makes a 123 a better candidate for conversion than an early 124. There's a reason Benz later switched to the larger 10P17c compressor.

OK, 'nuff rambling for today,

- JimY

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