ES 134 industrial 134A replacement
Yes pulled vacuum for 1 hour

Great thread, and very timely for me.
I want to upgrade my 1982 300SD ( W126--Gen1) as much as I can while I have it in the shop.
What pieces do I need from my 1991 300SE (W126--Gen2) ?
I already grabbed the condenser.
I plan on new compressor, receiver-drier, and expansion valve.
What is the best choice for compressor? Do I need a mounting kit?
I plan on using R134 because it is easily available, but if R12 is required to get it really cool in the Mid Atlantic's high heat and humidity--tell me now. ( I have R134 gauges and a vacuum pump)
Anything else to know?

Your 1991 compressor won't fit your 1982 under any condition. You need a Sanden conversion from Klimakit or forum member Rollguy if you want to delete the idiotic R4.


The condenser is an unknown. It may or may not fit, the only way to find out is try it and see. You will need custom hoses to make it work. You might be better off building a parallel flow condenser to fit your existing space.


You should transfer the dual aux fans from your 1991. They will fit the existing space, but you'll need to transfer over the rod that the horns mount to. Depending on whether the holes are pre-drilled in the radiator crossmember or not, you may need to do some drilling for some bolt holes.


The upgraded condenser, compressor, and aux fans should do fine with R134a. The condenser and the puny aux fan are the primary limiting factors in the W123's and Gen I W126's. The evaporator and HVAC box are largely the same between the Gen I and Gen II, although the Gen II's have a much more powerful blower.

I run R134a and tested my vent temps yesterday:

Vent: 46F
Outside: 82F
Humidity: High
Low interior fan speed
Good fan clutch (Engine doesn't go above 90C in traffic at 80F outside)

Except for the R134a everything else is stock

When the sky is cloudy or at nighttime I have to have a slight heater running with the a/c because it just gets too cold.

We took my car on a short road trip this afternoon. No window tint, factory setup other than reseal, replacement wear parts (TXV, dryer, pressure switches, O-rings, Shrader cores), and properly charged 134a.


Temp Wheel: ~70F (border where white meets blue)

Vent: 46-48F
Outside: 86F
Humidity: High (hazy because it stormed last night)
Sun: High

Fan speed: Auto (running med-high to med-low after cabin pulled down)


Car sat in direct sunlight from 10:30AM - 4:30PM. Interior hot to the touch. Was cranking out cold by the time we'd navigated the feeder road and gotten on the Interstate.

[QUOTE=Diseasel300;4047164]Your 1991 compressor won't fit your 1982 under any condition. You need a Sanden conversion from Klimakit or forum member Rollguy if you want to delete the idiotic R4.

Thanks for info---that was about what i had assumed, but confirmation is always good.

Yes, I was not planning on using the compressor.
I already got the dual fan assembly from the '91. It looks like the mounting holes are there.

Quick question, why there is R134 A sticker on the expansion valves ? are there specific valves for R12 and R134 ? I thought the expansion valves are designed for any type of refrigerant

Expansion valves have different spring rates in the powerhead and different orifice sizes for different gasses. R12 is a larger molecule and runs at a lower pressure than R134a. As a result, R12 has a weaker spring and a larger orifice for the same capacity compared to R134a. You can run R134a on an R12 expansion valve, but you lose a fair bit of capacity in the system. If you run R12 on an R134a expansion valve you will run low suction pressure and can ice the coil (along with reduced system capacity).

It's a big reason why I constantly beat the dead horse of "always change the expansion valve" when redoing the A/C system or converting to R134a. It matters. R12 was banned by the Montreal Protocol in the early 1990s and you won't find service parts for R12 systems anymore. If you plan to run R12, you must run the original expansion valve, not a replacement which will be for R134a.

This is the part i bought of Ebay, I was looking for MB brand nor aftermarket junk.

New Genuine Mercedes-Benz Valve A/C - Expansion 126830038464 OEM
Condition: New
Brand: Mercedes-Benz
Warranty: Lifetime
Manufacturer Part Number: 126-830-03-84-64
Fitment Type: Direct Replacement
Other Part Number: 126830038464
Superseded Part Number: 1268300384

Diseasel300 - wow; you are really a fount of information. Have never seen that explanation about R12 vs 134a. Now I understand a bit more.

Thanks for that.

That is the latest part number for the Gen II 126. The OE supplier for Mercedes was Egelhof/ACM. Pretty much anything made after 1993 should be marked for R134a and be a silver colored body. The original R12 expansion valves were a gold color. I've used Egelhof/ACM valves on every German car I've done A/C on and never had an issue so you should be fine with them or MB.

The heat capacity of the 2 gasses is different as a result of their molecular composition. The R134a needs to run at an elevated pressure compared to R12 and reject more heat to do the same amount of work in the same system. If everything is perfect and all the planets are aligned, the gas in the condenser will just be leaving the final loop as a liquid. In the real world, the last loop or two in the condenser will be liquid depending on ambient conditions.


If the charge is low, or the wrong metering device is installed, the head pressure does not build adequately to condense the gas to a liquid. That is where you get the flashing sight glass and poor cooling performance, the expansion valve is open too far to allow head pressure to build sufficiently to condense the gas due to a low volumetric charge. On a very hot day with high humidity, these systems will run a 250-275PSI head pressure vs 200-225PSi on R12.



Converse to popular opinion, you need the pressure and you need the heat in the system to do work. The people who stack 2 parallel flow condensers on top of each other are defeating the purpose of the the condenser. The first one condenses the gas, the 2nd one is acting as a liquid receiver, the result being a gross overcharging of the system and very poor cooling performance in cooler or temperate weather. W123 and Gen I W126 cars need an updated condenser to run R134a, they were barely adequate to run R12. The Gen II's are a different story, no upgrade required. The stock system will handle it just fine with a replacement expansion valve and the correct oil.

Aftermarket monovalves are known to be bad in these cars. Get a nerw one from Mercedes.

Good info. Do you know if there is an R134 expansion valve available for the 560SL?

Currently just using aftermarket replacement which I assume are designed for R12.

I don't know on the 107s. My 500SL has had the A/C broken since 1998 and I've never torn into it to repair it. The front seal on the compressor is blown, any gas you dump in sprays right back out. I should get off my butt and fix it so it gets used more. I've never laid hands on anything on that system other than the charging ports, so I'm not sure if they use the block-style expansion valve, or the old-school bulb style.