Probably a wise decision. AC is unlike any other system in the car. Proper charge and oil amount are absolutely critical. As is knowing low and high side pressures and temps during operation. Also, ambient temps are important when this work is being done. Can you "shotgun" it and have good results? Sure, it's called luck.
You've obviously spent some money on it. With the rebuilt compressor and PF condenser (new filter/dryer, too I hope), should be nice and cold. I'd leave it to the pros...

Oil & Operating Pressures
 

Thanx, I'm hoping some one will post the low side pressure of their system when it's working properly .

Yes, too much oil will indeed raise the vent temps but first I'd look at the operating pressure as too high with R134a will quickly reduce the systems ability to shed heat, causing warmer dash vents .

I've talked to quite a few AC shops and none will watch the pressures, they want to either go by weight (there's a scale that holds the can, as the can empties you can see the weight go down) and others (most it seems) will use a fancy machine that you put in the vehicle info or the amount of charge from the sticker on the core support and press 'GO' and it does it automatically from a large Freon tank .

This isn't any good because our W123 cars were specc'd out for R12 and you need less volume and weight and pressure when using R134a so it's not quite "shotgunning" it .

I don't want to add too much .

This morning before sunup it was 69* F outside, at freeway speed I was getting 48* F at the dash vents, I'm sure it'll do better than that .

Don't be in too much of a rush to flush the system, yes flushing is a very good thing but you need to flush the evaporator too or there's no point .

I'd avoid any "ac shop" that didnt pay attention to the pressures. Pressure tells you the temp of the refrigerant. The lower the pressure the lower the temp. Pressure and temperature are directly proportional in an ac system. If low side pressures are too low you run the risk of freezing the evaporator. There is no 1 correct pressure. Varies from system to system. If you're "shotgunning", gotta know "ballparks"....

Sorry Nate, I don't know my pressures. I don't have a gauge

Since this looks like a general A/C thread - I've been looking into W123 parallel flow condensers and see that some people have installed dual condensers. There's a 14"x23"x44mm double-thickness parallel flow condenser on AliExpress that looks appealing to me. I could have a local A/C shop make hardlines for it to connect to the stock W123 hoses. If I've measured it right, there would be roughly 1/2" between the condenser and radiator.

I added a W126 aux. fan plus manual override switch to my '80 240d to help stop-and-go A/C performance, which is somewhat passable (about 35 degree drop) but I want better. It might also be possible to install a higher volume interior fan from a different car too.

Here's a fairly short overview/article of what's goin on with the ac in your car. It gets pretty "deep", but try and hang in there and get a general understanding. The previously posted "chart" is good if you want to know what pressures R134 is at various ambient temps. Unfortunately, ambient temp isn't really what you need to know. Kindly observe the charts at the bottom of the page. What they show is the temperature of the REFRIGERANT for a given PRESSURE. So, you need to know the pressure in your system (both high and low sides) aka "suction and discharge", in order to determine what's goin on with the refrigerant. Using the first chart, find 32 degrees F. You'll see the R134 pressure is around 28 psi. In other words, that would be your evaporator or low side pressure/temp and it's right around freezing (too cold). Let's say you want to keep your evaporator from freezing (good idea), so at 35 degrees F. the pressure should be around 30 psi. These pressures are read at the gauges that are connected to the high and low pressure sides of the ac in the car.
Keep in mind this an EXTREMELY simplistic example, I have just given, and not meant, BY ANY MEANS, to be used as any kind of instruction or direction.
Also keep in mind, before charging a system (if it's completely flat-no pressure) it must be evacuated first. Drawn into a vacuum. All traces of air must be removed. AC is a complicated, skilled trade. Yes, "anyone" can mess around with it and maybe have a bit of success. You can also waste a lot of money unnecessarily, possibly ruin a new compressor. And finally, it's a bit dangerous. Eye protection and gloves are a must. Freon under pressure can cause serious burns (freeze burns) and systems under pressure can burst throwing parts all over.
I'm no expert and not trying to discourage anyone. Just be careful. I've had the good fortune of a very good friend who's an expert in the field and has had me "under his wing" for a few decades. I wouldn't know anything if not for him (and I don't know much).
Not sure who gets credit for this phrase (one of my favorites), but it definitely applies here: "A little knowledge can be a dangerous thing".
Stay frosty, my friends. And, be cautious. Please!

Pressure-Temperation Relation, Superheat and Sub-cooling - NETHMAL PERERA (EIT) BSc Mechanical Engineering

Not much. I did all the work myself. A few hundred in parts. I did the same to my 65 f100 which had amazing results. Much bigger of condenser on that truck and a Sanden 5. The pf condenser was a cheapie on eBay. I made the hoses out of Galaxy and Futura barrier hose with fittings I bought on eBay. I used two driers because I had to crack the system twice 1st when I discovered one of the old hoses had a slow leak, then second when I added the of condenser. Each time I added a little PAG oil to make up for what I thought spilled out on the floor. I may have put in too much.

Wow, I'm impressed. Way to keep costs down. Dryer is about the cheapest part of the whole system, so no biggie. Would love to see some pics! Or, maybe a parts list and sources. You did a great job! Cheers!

123- I have a photo rich thread here. Posts 100 and up show the AC work which was done off and on for a year. I mention most of the places I got the stuff. Basically eBay motors sellers who specialize in custom AC parts. It was surprisingly inexpensive. THe 300D cost me about $500 in parts because it included new pods and electronics and the truck was $300 because it was a more primitive system.

The one thing I didn’t mention is the u bend em tubes from vintage air that I used on my pickup. Available from Summit. I didn’t use them on the 300d but they would have come in very handy for fitting the pf condenser in the tight quarters.

http://www.peachparts.com/shopforum/diesel-discussion/394730-got-1985-300d-turbo-7.html

U bend em. I had no idea how to flare AC o ring fittings so I bought these to do the hard lines in my pickup. On the pickup I ripped out it’s old under dash York based system and cobbled together a condenser, evap, Sanden 5 and hoses. If I turn the mechanical bulb thermostat down too low I can see ice forming on the evaporator. All with 134a. It must be the giant of condenser I fit on the truck. The evaporator was a Mustang replacement IIRC.

https://live.staticflickr.com/65535/...33a6e1e366.jpg

https://www.summitracing.com/search/product-line/vintage-air-u-bend-em-refrigerant-lines

I learned most of what I did off the guys here. Basically I bought a bunch of parts and bolted them together. My system is solid and doesn’t leak. The subtleties of refilling 134a and oiling a pf condenser are still vague.

THANK YOU for the links and pressure chart ! .