W123 300TD (1982) Air Conditioning rebuild advice
 

It's finally time to get my air conditioning operational. I'm seeking any and all advice.


My system is completely unpressurized and is missing the condenser, fan and several hoses. My mechanic is R12 licensed so I'll be using that rather than R134a.


So far my parts list is:

• Hoses
• Condenser
• Fan
• Receiver Drier (I read these should be replaced whenever the system has been evacuated)
• Expansion valve (these are cheap so why not replace it?)

Anything else I should replace while the system is unpressurized?
Any suggestions on finding a Condenser? Pelican appears to not sell them.
Any thoughts on after market Driers which are much cheaper than MB?


Thanks in advance for sharing your wisdom!

Do you know why it was left in that state?

Consider a new compressor, aftermarket drier is fine, a parallel flow aftermarket condenser (someone please comment if parallell is no good for R12), AC flush for the lines and evaporator, coil cleaner for the outside of the evaporator.

Search for how forum members have figured out workarounds to get the outside of the evaporator clean. It improves the airflow and gives a lower air duct temp.

It is a big task but doable. Good luck!!!

When I bought the car the AC was non-op and missing the aux fan. When I replaced the radiator I also discarded the condenser and some of the lines, thinking I was unlikely to ever fix the AC.





I had the entire engine replaced with a rebuilt engine and the compressor supposedly works fine. Thanks for all the tips!

Were the ports on the back of the compressor sealed? if yes, ok. If no that is a problem. Early R4 compressors used O-rings at the back of the compressor, later ones used flat disc seals, you may need an adaptor kit but if you're having hoses made perhaps the adaptor could be avoided.

Ask the person doing the recharge to pull the vacuum/evacuate for several hours, this is how the moisture is removed, it decreases the boiling point due to the vacuum and the moisture boils out. Then let it sit for an hour to see if it holds the vacuum.

Next if they are an AC shop, pressurize the system with nitrogen to see if it holds pressure...nitrogen is cheap. If not AC specialists they may not have the nitrogen.

Good luck!!!

A/C Resurection
 

Mostly the things have been covered .

use the largest condenser you can squeeze in ~ it's the easiest way to increase system performance .

The last thing I knew, all the W126 expansion valves were marked 'for R134a only' ~ R12 and R134a have different working pressures so do the research .

Consider overhauling the HVAC blower motor or a new one and the fan speed control may need re capping too....

Dot every "I" and cross every "T" and you'll like the AC , maybe not the folks in the way back seat but it does work well when everything is 'Just So' .

If you wind up using a new compressor, I highly recommend the Japanese SANDEN 7 series upgrade .

Where do you get new hoses for the system? Mine are original and showing deep cracks.

AC Hoses
 

Many AC shops are set up to make custom hoses, do some research or buy new ones, they're still available last time I checked .

I'm in the same boat. Where did you source your compressor from?

Of course, I agree. 300TD1982- Since you are replacing the condenser, I suggest:
https://www.ebay.com/itm/CNFP1620-AC-Universal-Condenser-Parallel-Flow-16-x-20-w-6-8-Ports/183684619401?hash=item2ac474dc89:g:94wAAOSwAWNcZH8y


If you decide to go with the Sanden, you need this:
https://www.ebay.com/itm/353068897521
as well as the mount kit and new hoses.



If retaining the R4 and going with PF condenser, you will need to at least replace the hoses that connect to the condenser. I would suggest replacing ALL the rest of the hoses as well, they are 30+ years old.......Rich

Sugar Bear, you have the vacuum and leak test in the wrong order. Always leak test FIRST with dry gas. If no leaks, then vacuum and charge. If leaks are found, fix and test again. This is the proper way. Using vacuum to test for leaks is NEVER correct or a valid way to test for leaks.

ROLLGUY,
You are correct, good catch!
Thank you.

You are welcome. This is for the newbees- Many (including myself) have learned the hard way. The standard DIY vac and charge on these cars may work once in a while, but for the most part, a couple weeks to a month at best. They most always have leaks, and the only reliable way to test is with pressure before a vac and charge. This is especially true with R134a. It has smaller molecules than R12, so a hose that might not have leaked with R12, will surely leak with R134a. Also, with the R4, there is NO OIL SUMP. When refrigerant leaks, the oil leaks with it. Often when a DIY recharge is done, a complete flush and proper oil charge is NOT part of the job. This oversight usually ends up in disaster for an R4. With no or very little oil circulating, the compressor will seize, and/or spread it's innards throughout the system. If a proper flush is not done BEFORE installing a new or rebuilt compressor, that compressor may not last long. Also, the old mineral oil that is left in the system is not compatible with PAG and R134a (used in most new/rebuilt compressors). It is imperative that all these steps be followed precisely if one desires their new compressor to last more than a month or season (at best).

Before deciding to go the Sanden route, I experienced all the bad scenarios that are possible with the R4. If one desires a long lasting A/C system in their 'Benz, follow these steps:
*If possible, leak check before removing/replacing any equipment
*replace any bad, or all old hoses and Orings
*flush all remaining hoses, evaporator, and condenser (Parallel Flow
condensers must be replaced, they can't be flushed properly)
*if DIY charge, add the proper type and amount of oil before installing
components. Dye is recommended for leak checking after charge
*install the new compressor noting what type and amount of oil came with
compressor
*if replacing expansion valve, be sure to replace with one compatible with
the refrigerant you are using
*replace receiver/drier, and leave capped until hooking the last two hoses to
it.
*check for leaks with dry gas, repair any leaks
*for pro charge, add the proper type and amount of oil with charge machine
and then charge with the proper amount of refrigerant (gauges with R134a,
sight glass with R12)
*check for leaks with UV light or sniffer (or both).


It is important to note what type and amount of oil is in the new/rebuilt compressor that is being used. If your compressor came with PAG (for R134a), and you are running R12, you MUST drain the compressor and flush the system, as PAG and mineral oils are not compatible. If you are not sure what oil is in your compressor, it is best to start "with a clean slate". Ester oil is compatible with both refrigerants, so that is what I use. The typical system needs 8 ounces of oil to work properly. If one does not know the amount of oil in their new compressor, or looses some upon installation (common with the ports being on the low side in a 'Benz), it is best to just drain the compressor, and add the proper amount of oil to the other components (or during the charge process). This way, you know that there is enough oil in the system. Even if draining the oil from the compressor, there is enough oil inside for start-up. The oil will then circulate with the refrigerant.

Id do every and any o-ring that you can, and also replace the schraders, since they can leak. If you can get some good metal caps with good orings that can be good too.

As I understand it, some older AC hoses rely upon oil flowing to help serve as a barrier. Newer hose materials are intrinsically "barrier" hoses. So where it makes sense to easily replace, you might want to.

Id recommend, especially if going with R-12, to get a receiver dryer that has a sight glass. Im personally not a fan of those which you cant see into...

Yes, all good points. I have not seen a single drier with a 123 or 126 part number without a sight glass. Newer vehicles made to run R134a do not have a sight glass.

Follow Up
 

O.K. then ;

I just came home from a week long road trip to Nevada in my 1982 240D with it's Rich SANDEN and parallel flow condenser modification , I never had to turn the AC off even on the hills it didn't want to pull 4th gear in (fully loaded, 4 people and trunk stuffed full) , I merely waited until the engine began to labor and down shifted into 3rd gear and cruised up the hill and over the pass easily, the engine never exceeded 95* ~ 100* C the entire time and often the dash vents were blowing 48* F , out side temps ranged from 113* F to 106* F , mostly remained at 108* F .

I have two other W123's with this get up and both are not working properly at the moment, we'll see what the issues are, leaks I think .

The flushing of the entire system is important as is the typ and quantity of oil used ~ some time ago a Mechanic in my old shop slapped a new DELCO R4 compressor into one of his own vehicles, (it was noisy so he changed it before it failed), vacuumed they system then added oil and charged it, was not happy that it no longer blew ice cold and so looked in the box for the new compressor instructions and found a BIG note : NOTICE : THIS NEW DELCO COMPRESSOR COMES FULL OF OIL ~ DO NOT ADD ANY AND BE SURE TO FLUSH THE SYSTEM BEFORE INSTALLATION .

Simply having too much oil sharply reduced the ability of the system to produce heat free air....

The devil is always in the details .