I remember a 124 article done by ackits a long time ago, and they basically said that it was the worst candidate for 134 conversion they had ever seen. Maybe that's what led to the major league souping up of the system.

Thanks for the thread...
He mentions:

100F ambient
"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."

Well I am getting like 60psi low and 340psi high...and I am not overfilled. I am in fact, almost underfilled. FSM states I need 80% of R12 amount, I have 60% in the system. It was less than 2x12oz cans, so about 20oz. I was concerned over the high pressures, so I completely flushed the system thinking maybe it was overfilled with oil or sludge and replaced the TXV and drier, it dropped pressures a little, but not much (it was 65psi low and 360psi high before) INCLUDING aux fan on high the entire time. The system just stopped taking anymore out of the 2nd can. I put it in ice water ran at 2000rpm -- wouldn't take it in and no wonder with those pressures...

What kind of cold temp. are you getting at the vents for both cars? The car I picked up recently claims it has 134 in it without the proper nipples. I suspect it is still R12 inside. Will likely get rid of the 134 and return system to R12.

Unfortunately enough time has passed that I have no recollection how much R-134 was used in my conversion. I am thinking it was about two cans, so roughly a 60% charge.

If you're seeing 340/60 with the engine running at 2,000RPM, then I think you are overcharged. I suggest recovering some refrigerant until the low side settles in at 35ish PSI with the engine at 2,000RPM. Don't fixate on the 80% rule for converted systems, focus on the pressures. You want to hit the target low side pressure without exceeding a reasonable high side pressure - that's how I charge conversions.

Remember, the boiling point of the refrigerant is controlled by the low side pressure. The lower the pressure, the lower the temperature at which it boils. If you have 60PSI low side, about 60 degrees is as cold as the evaportor will ever get. (Need to look up the temp for 60PSI for R-134a; I don't have a pressure/temperature chart handy.) In an overcharged system the rise in low side pressure means the evaporator will never drop below the corresponding temperature, regardless of whether enough BTUs can be removed or not, hence resulting in inadequate cooling complaints.

Here's a chart:
http://www.idqusa.com/app/_files/Ima...art-33776F.jpg
http://www.idqusa.com/app/_files/Image/r134apc(1).jpg


It looks like you're pressures are too high. I'd agree with jcychun, looks like a bit overfilled. Back it down to the recommended levels in the chart and check performance.

I've had SEVERAL conversions end up in the 60 to 65% range. I haven't done one in a while, but if I did, or I was recharging one already converted, I would start with 60%.

My best conversion has been my 88 Vette. It has 65% and makes 38 at the vent even on a really hot day. I was amazed at this because a bunch of people told me that they were terrible candidates for conversion.

I agree that your pressures are high. If using less than 60% improves system performance this will be close to amazing, but also very interesting.

Thanks for keeping us posted on all this.

As I said, I am not overcharged. I have less than 2 cans in it. 20oz at most.
I've evac'd and recharged 3x total. Im not overcharged....

60 PSI on the low side at 1000 RPM is still way higher than I would expect. If you tap on the TX valve does it change?

FWIW at that RPM my car is at about 25 PSI. At idle it is at about 40 PSI on the low side.

-J

That is a fantastic idea to bypass the heater core but I need to know more about the resistor, is that because you want the fan running more often?
tx carmen

Doing some thinking....

What about creating a misting system for the condenser? I bet that would resolve all issues extremely cheap since I know my A/C can pull 40F from the vents on 90F days.

Radiator Mist Cooling System

I still have the lines for the OE wiper unit, but I have aftermarket DEPO Euro headlights now....so I have lines pretty much running both sides if I could make it work with the washer reservoir.

For what it's worth, I suffered from inadequate a/c in my 88 300CE for a long time, replacing various parts. When I finally got rid of the original compressor and replaced it with the 90-95 version part # 0002300511, it finally dramatically improved. Since then, I have no complaints about it and my kids in the back sometimes complain they're too cold.

The 0002300511 compressor is made for R134a, so it must be better at cooling at the higher pressures.

I was reviewing the wiring diagrams for the the W126 with dual fans, and according to the FSM the high speed isn't fused :eek:

My car has an un used strip fuse location, I might install one for the high speed.


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My 190e 2.6 has twin fans ahead of the condensor...
Could be made to work...

This sounds about right, I don't recall encountering any in the cars I've worked on.

My 190E has dual fans that draw about 30 amps total. I have them modified so that I can turn them full power manually. I've also removed the resistor..

I probably should put a fuse on the power line though. It comes off the battery and runs to two relays (one for each fan)... I think I actually used the car's old alternator cable as the wire.. (since upgraded to 0 gauge for the 143amp)