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  • 600SL
    replied
    Big success on the AC. These taken 81° F ambient 65% RH, using standard test conditions, engine at 2000RPM windows down, blower high, recirc off. Also checked evaporator temp operation. Engine at idle, blower low, windows closed recirc on. Clutch cycled off at 32°F back on at 36° F.

    AC is done.

    Now time to check if I have cooling system issues. I have a 12 hr drive coming up in a couple of weeks to NY. It should be hot and a really good test of all systems.
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  • 600SL
    replied
    Attempted to check sub cooling yesterday, but no luck. My $30 4 channel digital thermometer turned out to be useless. I put it in an ice water bath to these it and at one time all 4 channels were reading about 110° F. Then I was able to get it to work briefly but it seams as soon as I start the engine all goes to hell. I couldn't get 2 TC to be within 30° of each other. But while I was calibrating I also checked my analog duct gauge and also found that to be reading high. So my duct temperatures are at least 10° cooler that I thought. I will be getting a new one of those shortly. But I will need to hold out for a better laboratory grade digital TC system.

    So at this time I'm considering the AC system complete. High side pressures are still within or close to MB specifications but there will be opportunity to drop them with the addition of a shrouded radiator fan. I need to go back to NY in a few weeks so will use that 12 hour drive as a good test of the system. I also need to verify the cooling system performance on some good hot days.
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  • 600SL
    replied
    Back from NY. Over the next several days. I will be testing to see how things are going. One of the things I noticed the last time I charged it was that the yellow charging hose was completely filled with oil after evacuating the system. I have never seen that much oil come out of a charging hose when purging the hose to add the Freon. Its leading me to believe that perhaps the differences in the condensers may just require less oil. While the original serpentine condenser has about the same volume as the replacement parallel flow condenser, the original is all tubes, whereas the parallel flow has most of its volume in the headers. So I do see the possibility of oil pooling in the headers. This would not have been as apparent the first time I charged as all of the oil would have been in the compressor at that point.I cant measure how much oil I removed or how much went out the vacuum pump. But I will estimate the original 120cc' is now below 100cc's. Perhaps that all this system needs to work correctly. I should know more in a few days.

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  • 600SL
    replied
    Got everything installed and up an running. Some good news some bad news. On first attempt the copper cone seal was not seated properly and leaked immediately. I was always afraid of this happening and this time it did. I hope I diden't cause a scratch in the sealing surfaces on either the TXV or Evaporator. So far I cant detect anything with my leak detector but I need to get ready top get on the road. Replaced the seal and successfully charged 32.5 oz. I diden't want to go any more than that at the moment because that's about 2 oz more than my calculation say is required, but sub cool is still only at 4°. When I get back I may try a bit more.

    Ambient temp today was 82°.
    High side pressure was 215PSI
    Low side pressure was still low at 14PSI
    But Duct temp was down to a cool 44°F

    I have no idea why the low side will not come up but the high side looks a little better. I will have a little more testing to do when I get back.

    In the mean time, Thanks for all your help.
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  • Cornbinder89
    replied
    Still report back, even if it takes a few weeks. We all learn by what works and what doesn't so know how your system responds is important. I was really hoping you'd find something in the old Tx, but it could be stuck or have something deep inside.

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  • 600SL
    replied
    Everything is installed except for 1 fitting. That should be in tomorrow. Hopefully I can get that fitting in, install the receiver drier, charge and do a quick test. Unfortunately I wont be able to do any more because I have to depart to NY on Sunday and will be gone for at least two weeks.

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  • Cornbinder89
    replied
    Best of luck, and let us know how it turns out.

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  • 600SL
    replied
    Well I'm hoping its the TXV. The new one came in as I was typing the last response. Even though I look on their web sight it says they didn't ship it yet. Except for the name on it, it looks exactly the same. Only cost 3 times the price. Both made in China probably at the same factory. My only hope is that 4 Seasons holds them to stricter quality standards. The other company URO has no quality standards that I can see, but sometimes they are the only parts available. It would not supersize me if URO was a rejected parts clearing house.

    For me to do a spray water test for a long enough time to get things to stabilize I will need to find a helper. That seams to be very difficult around here. My wife finds the hose very heavy when shes spraying it at a car. But it seems to miraculously lighten up when shes spraying the garden. But I will get it done if I have to prop the hose on a stand or something.

    And as you say the Mercedes 560SL is a marginal system to begin with. But when I first ran it, I thought the parallel flow condenser was working magic. Hopefully I will be able to install it tomorrow but I doubt I will have it ready until the weekend.

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  • Cornbinder89
    replied
    Well something is causing the low side to be that low, It indicates not enough liquid refrigerant is making it into the evaporator. One possibility is the Tx valve. Another is the refrigerant is not fully condensing an the Tx is trying to meter a mix of liquid and vapor. For that to happen there would have to be a problem with the compressor, preventing the pressure to rise to the condensing temp/pressure. That doesn't seam likely because if the compressor couldn't compress it couldn't pump the low side well either.
    I have found many systems are made just good enough to be passable if nothing goes wrong, degrades or any changes are made that effect air flow.
    I posted my pressures to show what is possible with a system built for R 12 on R134a. My air cooled condensing temp/pressure was as good or better than yours with water spray.
    Systems can be forgiving to a point, but if you don't get the heat out of the refrigerant it gets recycled back to the evaporator. There is more to it that just higher pressures,

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  • 600SL
    replied
    I'm going by memory because I wasn't too concerned with it at the time, as I new the fans would need to fixed to a final solution, but if I recall it was a 70° ambient in my shop pressures were running 375, As soon as I jumped the radiator fan only it swung immediately down somewhere below 175. It was working so well it cooled my shop down to 65°, with both garage doors open, buy the time I finished charging. Currently most of the testing I do, at a stand still, at 2000 RPM gets the engine warm enough to turn on both fans to full speed. The standard Mercedes has a thermostatically controlled viscous mechanical fan plus an auxiliary fan up front. The Auxiliary fan comes on at low speed at 290 PSI According to the manual and comes on at high speed at 105°C. The low speed fan will shut off at 150PSI if the engine is below 105°C. Now the book says 290PSI But mine is kicking on at 260PSI, I'm OK with that. It does seam to kick off at 150PSI, so maybe the 290 in the manual is a typo because it seem high. I have my aux fan going to high speed at the pressure switch setting witch is currently at 260. Seems Mercedes logic is to at least get up to high pressure at least once and then the fan is essentially on because it wont go below 150 unless it cold out. And the newer Mercedes like the 96 SL600 that the engine came out of go to high speed fan with the pressure switch and low speed fan for all speeds below 40MPH. Its a little closer to what I have now.

    Your normal is defiantly not my normal, Iv'e never seen high side pressures that low in any of the vehicles I have worked on at least not at 90° ambient. But I have a feeling trucks have more room to work with than cars and cars especially mine are forced to stuff more stuff into less room and have to compromise more. If you look at that chart I provided somewhere in the beginning of this adventure it showed what they called normal pressure readings for an R134 system. They are in the 225+ range at 90°. Normal for Mercedes on the other chart I provided with R12 at 90°F = 32°C is 14bar to 16bar = 203PSI to 232PSI. So if I have to live with 250PSI on a 90° day, that's a compromise and I'm OK with that.

    In the mean time I talked with the guys that make the High performance fans and they were very honest. That I could not replace my 16" 2500 CFM fan with 4 8" 2400 CFM fans, or at least it would be a crap shoot. He recommended I find a company that makes 2500 CFM fans with a shroud and only a 2.625" depth. I spoke with them and they look like they look like they have a suitable product. They are called Cooling Components. At least I will be able to get a fan the size of the one I already have with the addition of a shroud, which I dont currently have.

    I also pulled my TXV. I did not find the clogged screen I suspected. But it still is a brand that has problems with all of their parts. They have a very bad name and consequently what I get for a $12 TXV. I hope I can find another brand, the 4 seasons one I ordered has not shipped yet. So I may still have to order from the UK. Last car I did had a 4 season and its been running for about 3 years now without issues.

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  • Cornbinder89
    replied
    I re read from the beginning, 1st and foremost, I am not there, so only know what you say and observe on your end. You said that after you "jumped the fan controller pressures dropped to "normal" What do you consider normal? It is 89 in the shade today and hotter where my truck is. I just finished installing a new evaporator and these are the pressures I see. OAT about 90, Dew point 70, engine fan set to run continuously. Truck fans are air on/off and will come to a stand still in the off position with the truck not moving, so need to be on when running the A/C and the truck is not moving. They have a pressure switch to turn them on, but rather than let it cycle on and off, I just turn it on when not moving. High side pressure 145-147 or between 105 and 110 condensing temp. Low side 26- 27 psi or 31-32 degs. Continuous stream of water off the condenser drain. I didn't bother to measure duct temp but it was blowing cool. It takes a good 30 -45 mins to cool down the heater box and ducts anyway There is some sub cooling at the condenser but I didn't measure it. All indications are the system is working to its capacity. A little higher engine speed and some forward motion and the pressures will likely drop a few points. I bring all this up, because if you are not seeing temps and pressures like this, your "normal" is different then my normal!
    I do think you have more than one problem. MY guess is either a bad Tx or a clog somewhere giving those low low side reading. I think air flow over the condenser is the other problem. The air has to make it through the grill and condenser but it also has to make it out, and not re-circulate back. Judging by the photo I see that as a real problem.
    Last edited by Cornbinder89; 06-10-2020, 08:22 AM.

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  • 600SL
    replied
    The mechanical fan was replaced by a 16" 2500 CFM electric fan behind the radiator. This as well was done for space. There is an opportunity to replace the 16" fan with 4 2400 CFM 8" fans. The front fan is the stock MB Aux fan used only for AC or when the engine exceeds 215°. That also has been moved as far forward as it can go and required slight frame modifications to do so. I certainly agree with you that I could use more condenser. But the real point of this thread is what happened between the time I first charged it with 36oz of Freon, when it cooled very well and now, where any level of Freon between 24 to 36 oz just gives me 60°+ duct temperature. So while I agree with you on the condenser being marginal, it did not get smaller since I first charged it. I really want to focus on what could have changed all by its self and the only thing I can think of is TXV got dirty. A new TXV is on order, It may take a week to get here so I may go dark for a bit, but I will be back. I'm also going to call Perma cool and ask them how they are getting 2400 CFM out of an 8 in fan. It actually rated at more than their 14" fans and allegedly on 4 amps. As far as engine cooling it does seam to be OK. About 10° hotter than before I installed the condenser, running 100°C on the highway in a 90° day. settles to about 105°C after getting off the highway and waiting in line for gas. I could possibly see it giving me problems climbing mountains on a hot day so more argument for more fan.

    As far as ducting and remote condensers they are all options but they are not trivial tasks. There is no space wasted in this car.

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  • Cornbinder89
    replied
    I never thought cost was the issue, if you can take on a project like that, $35 isn't going to break it.
    You have GOT to get the heat out, if you don't it will not work. Up to you if you can live without A/C.
    Does that have a mechanical driven fan at all, or is all being handled by electric's?
    Looking at how close the radiator is to the front of the engine, it seams that air flow is going to be a problem no matter what. You have electric fans little more than 2" from a solid wall, where is the hot air supposed to go? From where I sit engine cooling is going to be an issue never mind A/C.
    Even with a louvered hood I think you would have airflow problems.
    If you can't or will not increase the condenser before the radiator, then the only other suggestion is a remote condenser mounted out of the engine compartment.
    I'm not trying to be argumentative, I just don't see the airflow being able to cool the engine, let alone be able to have a condenser in front get enough flow to have good heat transfer.
    Can you duct air to a condenser that dumps into a wheel well? You'd have to make sure none of the underhood heat reached it.
    That pic is worth a 1000 words, I think airflow is the key.

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  • 600SL
    replied
    Its not the cost of new condensers I'm concerned with its the room. See the attached picture. In order to fit 4 more cylinders under this cars hood it was necessary to move the radiator forward 1" into the area where the stock condenser once was. The new condenser lost about 8% of area, I was hoping to get that back with parallel flow. Doubling up on condensers is not going to happen in this car. But additional fans might. I don't mind spending the money for 4 8" 2400 CFM fans to replace my 16" 2500 CFM fan, but that claim of 2400 CFM seems like a very tall tail, so I am a bit hesitant at the moment. I will defiantly try the TXV, The one from London cost $95.00 to ship. I can get a 4 Seasons one locally.
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  • Cornbinder89
    replied
    All you did by overchargeing is reduce the area in the condenser available to hot gas and instead filled it with hot liquid. You end result is that the heat is still there and still way too high. You are going in the wrong direction. Super heat and sub cooling aren't going to solve this. They are things used when engineers are designing the system. You have the system you have, so lets deal with that.
    1st I would change out the Tx, not expensive and it could be partially plugged. Next I would focus all my attention on getting the heat out at the condenser with the correct (30 oz?) charge in the system.
    Just because getting the heat out at the condenser isn't the easiest thing to achieve, doesn't mean it isn't the problem.
    At 280 psi the condensing temp ~155 deg F or over 70 deg above ambient! You are headed to burst hoses and compressor that will fail from too much heat and not enough lube.
    Either the condenser is too small for the system, you need a condenser that is at least capable of 1.5 ton, or the airflow thru the condenser is not good enough or is re-cycling heat from the engine.
    A/C can not survive with head pressures like you are seeing. Try standing in a spray of 155 deg water and see how cool you feel!
    It seams to me you are grasping at things because you don't want to face the fact heat is not being shed.
    Best mobile A/C system I have was designed for R12 running R134a, has a 1.5 ton Tx and evaporator but a condenser of over 30,000 BTU capacity! I get very low head pressures and very good cooling. The refrigerant is as close to ambient as possible, and the refrigerant oil stays cool. The difference in price between a condenser that was "just big enough" and the one I installed was less than $35, the difference in operation, is staggering. Yeah it was overkill, but is works well and components last, head pressure is low and the energy required is less (not that it is really a factor on a semi tractor). I fought marginal condenser capacity for years, and when new would just work, but once a little corrosion reduced heat transfer it was a battle to keep cool, head pressures rose and things started failing.

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