Not as much as it will a Gen 1 W126 or a W123. The small-tube dual-circuit condenser of the Gen II W126 is quite efficient. It also has the huge benefit that it can be flushed, a parallel flow condenser cannot and must be replaced if clogged or compressor fails.
Use PAO68 oil. It is usable with R12 or R134a. All of it goes in the compressor, the Densos have a sump and do not require the oil distributed around the system.

Replacement monovalve core should ONLY come from the dealer. They're expensive ($130 or so) but the only ones that work and last. An old hardened core will not work, the MTC aftermarket ones typically don't work properly either. Make sure your coolant hoses are routed correctly.

You have not confirmed whether or not the coil is energized with the A/C running, you can only test it properly with everything hooked up due to how the transistor pack in the pushbutton unit does its switching. Adding a manual valve is totally unnecessary, the monovalve should stop all water flow to the heater core when the temperature wheel is set to the blue dot (max cold).

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Personally I'll add probably 75 to 80% of oil to compressor then remainder in other parts, dryer, hose to condenser, etc.

__________________
Jim

Correct my information please is it 7.75 Oz ? the sticker under the hood does not say anything about compressor oil.

Thanks !!! great information out there !!! can you tell me more about the mono valve ? so the is coolant coming from the engine through metal hose them from the bottom of the valve, if the core pushed up the coolant will run into the heater core ? the core should be pushed in all way all the time unless you turn on the heater ?

If there is a tear in the rubber diaphragm within the monovalve assembly, then you will get hot coolant circulating in the heater core when you want a/c.

Parallel flow condenser will work **substantiallly** better with r134a than the original tube condenser which was designed for r12. The original r12 condensers the w123 and w126 chassis Mercedes came with will work with r134a but will have lackluster performance in hot weather. You can get universal parallel flow condensers, but you will also need to know how to make custom a/c hoses, which a good a/c shop can do. Cabin temps will be in the 40's with a parallel flow condenser and r134a.

https://www.youtube.com/watch?v=M5lvHxCVxWg

I ordered one from here, he raised the price today !!! he said he is getting more calls about them, his name is Matthew, one kit with brackets and hoses

https://klimakit.com/product/parallel-flow-condenser-upgrade-kit-w126/

I'm not so certain you could find a better price on a universal p flow condenser. Measure clearance and then find one that will fit with the fittings in the correct place.

I don't know what the total oil capacity is on this application.

__________________
Jim

Sure seems like a lot of money to throw after a solution that isn't the problem. These Gen II W126's blow mid 40s on a 100+ day running 134a. I don't know what you think the parallel flow condenser is going to achieve since the pushbutton unit switches off the compressor when the evaporator coil reaches 38-41˚ (42-44˚ vent temp). The Gen 1 (Pre-'86) cars are a totally different story.

I'm just waiting for the OP to come back complaining that his $300 coil and $100+ worth of R12 didn't fix his problem.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I have 3 spares climate controls, I plugged them before to test the system, no change at all, my compressor is running all the time I can tell from the clutch and the gas flowing on the glass sight, never seen my AC less that 53F from center vents since I bought the cars 4 years ago. its eaither full of oil or something else, even when I checked the service order from the dealership that the previous owner gave me, when he paid $4K to convert the AC to 134A at there, the note says (no leak detected, the system is holding pressure, the owner claimed the AC was blowing hot air from the center vent) after 4K and 3 months at the dealer ship as they ordered all the hoses from Germany, the note says (AC works fine, 50F is blowing from the center vents)

When the system is operating do you see any bubbles in the sight glass located on the receiver/drier?

I see one solid yellowish fluid flowing by. Its not clear, I remember my old 1988 VW Passat LS that has the same as Mercedes Benz AC system, the sight was clear on R12, buy I heard you can't get the sight clear in A134A, is that correct ? that was back in the 1991till 2003 when I owned the car

+1

Absolutely incorrect. If the charge is right in the weather we're having (I'm in Texas too), you should have a clear sight glass. ZERO bubbles in our current weather. Cloudy/foamy/bubbling/opaque sight glass indicates low charge. Yellow suggests they have dye in the system, that should not be present if the system didn't have a leak previously.


You're obsessed with throwing a LARGE amount of money into converting back to R12 when the refrigerant being used isn't the problem.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

R134A will, if low on freon, show bubbles in the sight glass. It ias amazing that the PO spent $4K to have the system converted to R134 A. Diseasel 300 is correct. There is still dye present in your system.

The last charge I used a scale, I charged exactly 2.03 lbs (70%) or 2.9 lbs of R12 (I hope my information is correct), Yes the glass sight was glowing as hell when I used UV light on it, I hope the dealer didn't flood the system with oil, do you think so ? that is why I decided to go the long way and flush the heck out the system, because this is my 4th time dealing with AC system. There was a leak before according to the dealer notes in the suction hose and they ordered one for him from Germany, the whole AC job took 3 month to get the parts, the car was sitting there.