I need to change out the AC compressor on a friends 300D. Almost all of the new or rebuilt compressors are R4 or R4/R12 compatible.

My question is if I put a newer R4 compatible compressor on what other pieces of the AC do I need to change out to convert to R4? Do I need to change out the Drier or Condenser or other parts of the AC system to be converted? or just the compressor?

Thanks.............

R4 versus R12 AC
 

Clancy,
You may be a little confused. The R4 refers to the type of AC comp. on your friends 300D."R"is for rotary and I believe 4 refers to the no. of cylinders. If you replace the compressor you should replace the reciever/drier to make your warranty on the comp. good. You can get the R-134 conversion kits from Auto Zone for $39.95. It includes all you will need plus three cans of R134. I have converted two of my MBs using the kits, and rebuilt comp. Compressor cost $99.95. Good luck and keep us posted on your progress.
Bill Lewallen Lexington,Ky.

Clancy -
 

You didn't specify the model year of your friend's 300D and
you've confused a type of automotive freon - R-134a - with the Harrison R-4 compressor that was used with the W123 equipped with the late style automatic climate control. Early W123 300Ds were equipped with York A/C compressors.

Unless you have auto A/C experience, this may be a job best left to professionals. Specialized tools are required (including a vacuum pump) and there are several decisions you'll have to make which will ultimately impact the A/C system's efficiency and longevity:

* Reason for compressor renewal? If the existing compressor seized, then you should replace the suction manifold that attaches to the compressor, in lieu of flushing. In the mid-'80s M-B released Service Information sheets indicating that hose flushing did not adequately remove metal particles from the hoses; unflushed particles would subsequently cause failures in renewed compressors.

* Compressor - new or rebuilt ? - new R-4 compressors are not particularly expensive and are far more reliable than rebuilt units. It's false economy to install anything but a new unit.

* Refrigerant - your freon choices are R-12 and R-134a; R-12, which requires a license to purchase, costs more than $35/lb; R-134a, less than $8. The maximum freon charge for an R-4 equipped 300D is approx 2.6 lbs of R-12, approx. 2.08 lbs for R-134. R-134a operates at a higher pressure and generally doesn't cool as well as R-12; higher operating pressures may precipitate failures in fatigued refrigerant hoses. Operating environment should be taken into consideration if you are looking for maximum cooling; in hotter climes the nod for cooling efficiency still goes to R-12. If you install R-134a, you may wish to consider installing a new R-134a calibrated expansion valve to achieve maximum cooling. Converting to R-134a will require installation of different Schrader valve fittings and the use of specific "O" rings to minimize leaks at charge valves and hose couplings.

* Refrigerant oil - R-134a requires a different oil (PAG) than R-12 (mineral oil) but apparently complete removal of existing mineral oil is not as critical as it was once thought to be. Either way, you must ensure that the correct volume of oil is present.

* Receiver/drier - should be replaced on principle, regardless of refrigerant choice.

* Condenser - does not require renewal during a R-134a conversion. But should be thoroughly flushed to remove existing oil and debris.

R4 versus R12 AC
 

The kits for conversion contain all information for converting to R134.I must be lucky because I have converted two of my MB diesles to R134.Air temp coming off the evaporator at max. blower speed is 38 degrees F. On Is six years old the other is onlt one year old. So far I have not had to add Freon in either car. Just luck. I don't think so. Just good work. Good luck to you.
Bill Lewallen Lexington.Ky.

Clancy,

You received some very good replies from some obviously experienced and wise folks.

I never can keep myself from responding to these posts.

First of all, it is correct that PAG oil is used with R134, but ONLY in those systems which have never seen R12. For a converted system, use Ester type oil only.

The combination of R134 and R12 is not good, it can coagulate and cause problems. If you insist on changing to R134, it is recommended that you flush the system thoroughly and pump it down for 24 hours.

There is a very valid reason for such a lengthy pump down. You need to get absolutely as much moisture traces as you can out of the system. Moisture combines with refrigerant which makes an acid which will eat up the system from the inside out. This situation is more prominent with R134.

Also, I'm pretty sure you can still legally purchase R12 as an individual, but only in quantities in excess of 30 pounds. Go figure. This law could have changed, but if it did, it was very recently. This means it will take hundreds of dollars to buy 30 pounds to get enough to charge your air conditioner.

And lastly, I have converted a few systems with the opposite results of William. Maybe it's incompetence on my part, but some of it is the fact that in 108 degree Texas heat, R134 just doesn't seem to cut it.

Best of luck,

I must clear up something about converting ACs to R134. I thourghly flush the system and use the ester oil that comes with the kit.I use a laboratory model vacuum pump. It is one we used in my lab and will almost reach a complete vacuum(30.00") I run the pump at least 4hrs. close all valves and let it set overnite. The next morning I will run the pump for another hour By this time there is nothing in the system. We don't hot weather like the folks in Tx.But is hot and humid here. If I remember my days in TX.,the weather was hot and dry. We sweat so much that we had to take salt pills.
Bill Lewallen Lexington,Ky.

I think William summed up the three most important points of this conversion: thoroughly flush and clean, use ester oil and pump down thoroughly, preferably with a wet vane pump. The lab pumps like William is using are outstanding, but expensive. I have a wet vane pump meant for refrigeration service. It is not as good as a lab pump, thus, I feel that 24 hours is the minimum for my setup.

I bad mouth the conversion because mine have not worked out well. That doesn't mean that they all will not work well. West Texas is dry heat, the Eastern part of the state gets pretty humid, the coastal part is only one step away from swimming through the air.

If I had a practical way to put in a bigger condensor, the 134 would probably work out pretty well for me.

Have a nice weekend,

Larry,
I know how you feel about the weather in Texas. I took basic training in Witchita Falls in July,1944. It was hot and dry. So dry our clothes didn't get wet with all the sweating. It evaporated too fast. We were required to take salt tablets to replenish the salt we were loosing.
How is your 240D rebuild comming along?
Try and stay cool and all the luck to you. Good luck of course.
Bill Lewallen Lexington, Ky.

Bill,

Actually even Wichita Falls is not as dry as it used to be. There are many more man made lakes as you go west which I believe have had an effect.

I have the four cylinder pretty much apart. All the rod bearings and journals are spoiled. The mains are so good I could just grind the rod journals and reuse main bearings and journals as is. I will not do that of course.

There was oil in the back cylinder, on the head gasket around that cylinder, and all around the back of the block below that cylinder. I just can't imagine that the head gasket could make a big enough hole to drop the oil pressure to nothing.

Unless I can determine for sure and for certain what caused the oil pressure loss, I won't put a bunch of money and time in this engine with such risk.

Thanks for your replies, I always enjoy them.

Have a great day,

My apologies to all, I was away for the weekend and was just able to look at the replies today. Thanks to all for your responses.

So OK, I get it......I would be converting from R-12 to R-134 if I change things out. Some asked for more info on the model of the car:

1984 300D Turbo

This friend is the realtor that sold me my house, she's has been wonderful to my wife and I so I want to help her out.

Thanks again to all.........