A/C restore questions - PeachParts Mercedes-Benz Forum

erubin · #1 05-02-2004, 04:47 AM

Will complete my '82 A/C restore tomorrow. Finished flushing today. All new R134 compatible o-rings, schraeder valves, Nylog, new compressor, exp valve and R/D. Will evacuate tomorrow immediately after installing the R/D. Just before that i will instal the compressor and load the oil. I will evacuate for a few hours with a vacuum pump I made from an old household refrigerator with soldered fittings.

Questions:

1. I bought an 8 oz squeeze bottle of BVA Auto 100 synthetic from ACkits. Does my stock system call for 6oz?
2. I am concerned that even if I load up the suction side of the compressor with oil on the bench and rotate as required about 10 times it will pour out as i wrestle it into the mounting position in the car. Can it be filled once installed, but wonder if gravity will tend to make the oil flow out before I have time to rotate the compressor.
3. How much of the oil should be spread out over the system or can/should it all go into the compressor? If it should also be loaded into the R/D, which port? I hope i dont need to put it into the exp valve as I already reattached it to the 4 hoses.
4. Should R134 get loaded based on weight, center vent temp or high/low pressures? I know the rule is 85% by weight of R12, but how much is that (i hope it is a multiple of my 12oz R134 cans)? Problem with using the high and low pressures meaures is that it will move around alot as the compressor kicks in and out and I suspect ambient conditions will affect the readings. Maybe center vent temp (go for the lowest) with a cautious eye on the gauges is the best way to go. If so what is the max pressue i should stay below? Tomorrow should be about as hot as it gets, about 90F and medium low humidity (40RH?) here in coastal LA. Should i park the car in the sun with windows and doors open or closed? I don't have a fan to put infront of the condensor but i could jump the cars cond fan if you think i should bother to figure out how to do that.
5. Is one 12 oz can or R134 with UV tracer and the ballance with straight R134 enough for leak detection (I have a UV light)?

Thanks for helping. I ask these questions even though some were already discussed in past posts but sometimes the posts gave conflicting advise.

leathermang · #2 05-02-2004, 07:56 AM

"sometimes the posts gave conflicting advise"
Not much way to fix that..... LOL.... As the writer Hemmingway once told a cub reporter.... " You have to develop a built in shock proof crap detector" ... (which is a lifetime job.... )

You have clearly done a lot of research.... and are doing some of the things usually skipped... like the fresh oil being added at the last moment....

With the prep you have done I would not suggest putting in the leak dye. There are reports of it gumming up stuff....and if you don't have a leak then you don't need it.

I do think that oil should be put directly into the R/D... just before you start evacuation.... and just after you open up the connections to the R/D. The other will circulate through the system naturally...and accumulate according to physics and gravity... but the R/D's function uses oil... so I would place it into there just as per the instructions when you only replace it.... measuring the amount which comes out of it... and replacing that same amount in the new one.

With all the good work you have done I suggest you go and rent a vacuum from a rental house.... unless you can describe where your vent is which will allow the moisture to drip OUTside of the system while evacuating it . Are you putting clean dry oil into that refrigerator compressor just before starting your drawdown ? Probably not...and I suspect you have no place to get the moisture OUT of the system.... while the refrig deal is cute for playing with.... I think it is penny wise and pound foolish to not have a good professional vacuum attached to your system for as long as you can manage... before adding refrigerant and sealing it up... ( hopefully for a long long time)... all of the things you have done have to do with and are dependant upon proper evacuation of moisture....

I would use weight to install . Find a way to measure the can if it is not a multiple of 12oz needed.... but err on the lower side....like 80 percent if you need to, then add more later if you need to.

What color Nylog are you using ?

What did you use to flush with ?

You did not say which compressor you are dealing with... are you sure there is not a plug for the installation of the compressor oil ? Some have ' crankcases' and some do not..... you do need to find out how much oil total your system needs... there are charts someplace....

Jetmugg · #3 05-02-2004, 10:27 AM

I'm not an A/C professional, but my research on this topic says - Forget the R134. Keep the system R12 if you want it to work properly. The price of R12 is dropping like a stone.

My 2 cents

SteveM

erubin · #4 05-02-2004, 01:00 PM

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Good point, I'll leave it out. I can always add it in the future if needed.

I just called all the rental places I could find in LA including some auto stores like Autozone and none have vacuum pumps. I really want to wrap this up today and I can't go buying a vac. pump mail order. The refr. pump has the old oil in it. I measured 28"HG with the suction side plugged. The pressure side is vented to atmosphere so that is how air/humidity is vented. It's not the greatest but it must be better than the venturi vacuum pumps some are using and I was told to avoid on this forum.

I flushed the system with 1 1/2 gallons of mineral spirits. I actually ran the spirits through the system several times and filtered it each time before loading the flush gun. Final flush was 2 qts of Dura 141 which has a very low boiling point and leaves no residue. I did so much flushing because I found some metal chunks in the condensor. The compressor (a rebuilt R4 installed by PO's mechanic) did not seize but it appears that it was starting to break down. No goo through out the system so I think it will be OK especially after all the reverse flow flush and a couple of forward flow flushes. I didn't change any hoses since they were not leaking. I would have liked to change them as well as the condensor but as with all projects you have to draw the line someplace.

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It's the R4 (no crankcase). Good point about the plug, it has a plastic shipping plug on the suction and pressure ports, I could put that back on after loading with oil just before installing in the car.

The Nylog is a dark color and it is made for R134 which is correct for me.

I am staying with inferior R134 for these reasons:
I live in a relatively cool not so humid environment (coastal LA). My family doesnt need ultimate coolin cause we grew up not really caring for AC anyway. Just need to take the edge off not bring it down to 70F in the car. Anywaythe R134 is a bit cheaper and easier to get for me.

It's time to get working. Will check in on this post in a few.

Thanks leathermang

leathermang · #5 05-02-2004, 03:08 PM

I did not mention the R12 because it was clear you had done plenty of reading up and would have already seen the arguements for keeping it...

"so that is how air/humidity is vented"
Well, I hope so.... but usually on a closed loop system the oil is circulating around and around... not like a vacuum pump specifically designed to have a place to exit the moisture pulled from another system... so what you may have is the moisture being deposited in the refrigerator .

Nylog--.... good... some don't know that there are two colors...

Yes, that compressor has no crankcase... all lube is from circulation....

It sounds like you understand how important flushing is....

That is too bad about not being able to rent or borrow a vacuum machine....most of the people I know... including me... are in the same situation.... can't really justify it for just their own cars...

Lots of people can get by with the r134.... it is usually the people with real heat problems that we try to impress with the better cooling characteristics of the r12 in these less than maximized systems.... my Ford truck will freeze you out with the r134a... but it was designed for and around its abilities....

Hope everything goes well....

erubin · #6 05-02-2004, 04:35 PM

OK, it's 90F out and everything is connected and lubed. The vacuum pump is pulling 29"HG per the devoted vacuum gauge I attached to my DIY vacuum pump. Water boils at 80F at 29"HG so I pretty happy with my setup and I'll drink a beer and think about all those nasty H2O molecules boiling out. But first i'll shut the vacuum pump and see if pressure stays steady proving that there are no leaks.

I understand that a deeper vacuum would be needed at lower temps so i'll just have to always work with >80F ambient when evacuating any cars in the future. I'll let it run for a few hours as it probably takes a long time for the trace amounts of H2O vapor to diffuse out through the vacuum pump. It's not like there is a big flow now that i'm down close to a complete vacuum so i'll use time to my advantage. Then it's R134 charge time.

The pressure port on my vacuum pump definetely pumped out air into the atmosphere as a vacuum was being created so i know it's not a closed loop. Would like to know how to change the oil (and type) in these refrigerator pumps for future use as i may be able to go even deeper in vac if it had fresh oil in there.

Thanks again leathermang

BTW, 29" HG is about 25,000 microns. It looks a lot worse when stated that way but who's counting microns anyway!

dmorrison · #7 05-02-2004, 04:54 PM

A couple of things.
You can add the oil into the suction side of the compressor at the conection where the suction line connects to the manifold line. This is a real convenient spot. HOWEVER you must crank the compressor by hand 10 revolutions or more to get the liquid oil past the compressor. The compressor CANNOT pass liquid without damaging it. Rotating the compressor by hand can be a pain with the compressor in the car. I made a tool to do this. A 3 pronged plate that fits in the front of the compressor clutch. It can be done by hand but a PITA. Add the oil to the manifold hose seal it and then install the R/D, then evacuate. The system calls for 42 oz of R12. @ 80% that means about 33oz ( @85% 35.7 oz )or just shy of 3 cans. After the first 2 cans are in then watch the vent temps for the last can. When the temp gets to its lowest temp you about right on the freon. Charging a R12 system with R134a is a hit and miss system. With a proper R134a charge you WILL have bubbles in the R/D window.
The vacuum pump your using! You shoud be able to pull 29.92 inches on a perfect day. To help the vacuum pump, heat the hoses and condensor to help boil the water out of the system. A heat gun or hair dyer will help.
The manual calls for 22 psi low and 265 psi high. Since your doing R134a your high side may be a little higher. Have you installed a binary switch in the R/D. this will help protect your system if the high pressure gets to high.
7.0 to 9.0 oz of oil in the sytem. Use the synthetic oil so you can go back to R12 without flushing.
And 2.66 Lbs of R12 freon.
Only 1 can of UV if you install it.
To jump the Aux fan, take the leads off the temp switch on the R/D. The verticle swtch not the horizontal one that is connected where the high pressure line goes into the R/D. Take the wires off the pigtail and connect them to each other. This will turn on the Aux fan when the car ignition switch is turned on.

Dave

Eric Eliel · #8 05-02-2004, 07:02 PM

Its probably too late for this but its easier to install the main manifold hose AND compressor as one unit. Bolt it together before you place it into the car. The compressor can then be filled with oil from the top before you attach the suction hose. You'll need a clean funnel with a narrow neck.

erubin · #9 05-02-2004, 07:58 PM

dmorrison,

Great tips, thank you. I don't know if it's a binary switch. i would suspect it is not. i did not change it. The binary switch will protect the system if it climbs to 30 bars. i doubt this could happen unless the condensor fan shut down with the AC running. This could happen if the fuse blows for example. I'll just take my chances now and put one in if and when I do another evacuation. If i go to R12 I guess i wont need the binary switch though.

The job is complete and here is what happened:
i loaded the compressor in the suction port with 4oz of oil on the bench and then spun it a bunch of times. Then i capped it with the plastic shipping cap. Only about a tablespoon of oil leaker out when i pulled the cap off after installing in the car. Not as bad as I expected. 2oz went into the R/D. So total oil is 6 oz, i hope that's enough.

Evacuated for about 2-3 hours at around 28.75-29"Hg. Ran car engine (with condensor fan off of course) to heat up the under hood area. Ambient was 90F and under the hood was even hotter.

Charged 3 12oz cans of straight R134 with condensor fan jumpered on after the first can was loaded. Here are my readings with car idling only, in the sun (90F ambient, 40RH), the blower on max and only center vents blowing:
high pressure: 290psi
low pressure: 39psi
temperature in center vents: 54F

Clearly R134 would not do in very hot humid areas but for us here in coastal So CA. It will be just fine for "taking the edge off". temperature should improve quite a bit if i speed up the engine from idle. i'll be checking when i take it for a spin. The hose coming into the exp valve is real hot (3 seconds threshhold of pain, which I estimate at about 130F). I guess the R12 designed condensor is not doing such a good job cooling the compressed R134.

I broke the temperature sensor on the R/D that triggers the cond fan to turn on by over tightening it. I'll do a search on this site for how to wire it so the fan goes on whenever the A/C is switched on. Is this a good idea, it'll save me $30 for a new part.

I used BVA Auto 100 synthetic compressor oil from ACkits. It's speced for R12 as well. It would be easy to go back to R12 i guess. I would do this if i got a hold of some R12 one day and the cooling capacity becomes unacceptable.

leathermang · #10 05-02-2004, 08:47 PM

Did you install a 134a expansion valve ? ( block valve).....

erubin · #11 05-03-2004, 02:30 AM

leathermang,

You've got me concerned now. i did not know there was an exp valve for R134 and different one for R12. The online catalog does not give you a choice. All i know is that the new exp valve i installed has the same part # on it as the one i replaced. The replaced one was installed by the PO's mechanic when it was converted to R134. the exp valve P/N is 126 830 0284.

Is this OK?

leathermang · #12 05-03-2004, 12:15 PM

I will go look at the number on my R12 block valve... but you ought to call Trey at Carlisle Auto air in San Antonio for the safest answer .... they have been doing this 20 years and are very helpful...

erubin · #13 05-05-2004, 02:10 PM

leathermang,

Parts suppliers don't carry a different exp valve for R134. It's the same as for R12.

I tweaked the AC a little more by releasing some R134 to reach the lowest vent temperature. probably only ended up releasing a few ounces. I had loaded 3 cans 12oz each which is slightly more than 85% of the R12 noramally used. here are my reading with the system optimized (only original design parts used, e.g. stock condensor).

Ambient 90F 40% RH
Condensor fan bridged on
Blower set to max
1500-2000RPM
Low pressure 25~30psi
High pressure 290-300psi
center duct temp 46F

For my climate this is adequate. For Texas type cliamtes maybe you need better.

BTW, keeping the engine on my diesel at 1500-2000RPM is tricky cause the engine seems to take off on its own even when i hold the accelerator steady. i don't have this problem with gas cars. is this a problem on my 300D or is this the case with all 300Ds?

I only loaded 6 oz of oil in the system. Some say it should be 8oz. i hope it's enough. If it isn't what should i do? Did not install the dual pressure switch on the R/D as Dmorrison suggested. i hope nothing blows up.

leathermang · #14 05-05-2004, 03:54 PM

It has been a year since I bought mine... but my AC guru told me to be sure I got the one for R12 since that is what I was going to use....
Have you seen this thread ?

original SDL expansion valve - R134a?

There should be different ones since the pressures/etc for the molecule are different ....

erubin · #15 05-05-2004, 06:23 PM

leathermang,

I spoke with Trey at Carlisle Auto air in San Antonio. He seems knowledgeable and said that the expansion valves now available are all designed for R134a. The new exp valves have R134a in the capillary tube and the old OE ones had R12 in the tube. He said the performance of my R134a will be fine with my new expansion valve and in fact will be fine if i convert to R12. He said the difference in performance between the two expansion valves is negligeable, not worth fretting over!

He did say something else that surprised me: the capillary tube should be unwound and clamped securely to the suction line (line that goes from the exp valve to the compressor).

Hard to believe cause the capillary tube is so short. I looked at the MB shop manual and they do not show this tube unwound and clamped to the suction hose. Lots of voodoo in the AC world! I guess i'll just leave it as i finished it--capillary tube wrapped up in the sticky (tar-like) insulation tape--and not bother unwinding it and trying to clamp it to the suction hose. With my luck it would probably break if I tried unwinding it.