W126 A/C questions/problems - PeachParts Mercedes-Benz Forum

Diseasel300 · #1 01-09-2020, 02:34 PM

The expansion valve can be accessed more easily if you remove the bolts holding the crash bar in place and dismount the crash bar. There are 2 bolts on the transmission hump and 1 or 2 up behind the cluster. If you choose to go without dismounting the crash bar, you'll be inventing new swear words, I can promise that (I've done it and don't recommend it). Crows foot wrenches are your friend, the skinnier the jaws, the better. Now is the time to replace the expansion valve as well, the original one has an orifice and power head setup for R12. The modern replacements have the orifice and power head setup for R134a which has a smaller molecule size and higher operating pressure. It makes a big difference in the final result, so worth the $30 or so for a new one.

Flushing the evaporator is best done with the expansion valve removed. Connect a hose to the discharge side and route it out of the car into a bucket. You can purchase Flushing kits on various websites such as Amazon. For a through flush, count on at least 2 quarts of flushing solvent, followed by plenty of air to blow out the residual solvent. I typically run 40PSI for flushing and 80PSI for blowing the lines out afterwards. Standing pressure of refrigerant in the system is >100PSI, so you're not going to be damaging anything from your shop air source.

Whaling · #2 01-09-2020, 03:33 PM

Quote:

Originally Posted by Diseasel300

The expansion valve can be accessed more easily if you remove the bolts holding the crash bar in place and dismount the crash bar. There are 2 bolts on the transmission hump and 1 or 2 up behind the cluster. If you choose to go without dismounting the crash bar, you'll be inventing new swear words, I can promise that (I've done it and don't recommend it). Crows foot wrenches are your friend, the skinnier the jaws, the better. Now is the time to replace the expansion valve as well, the original one has an orifice and power head setup for R12. The modern replacements have the orifice and power head setup for R134a which has a smaller molecule size and higher operating pressure. It makes a big difference in the final result, so worth the $30 or so for a new one.

Flushing the evaporator is best done with the expansion valve removed. Connect a hose to the discharge side and route it out of the car into a bucket. You can purchase Flushing kits on various websites such as Amazon. For a through flush, count on at least 2 quarts of flushing solvent, followed by plenty of air to blow out the residual solvent. I typically run 40PSI for flushing and 80PSI for blowing the lines out afterwards. Standing pressure of refrigerant in the system is >100PSI, so you're not going to be damaging anything from your shop air source.

Ok thank you for all the advice i really appreciate it i will probably put this project off for a week or 2 and tackle it then when im not so busy. I found what seems to be a good write up for removing the expansion valve. I will post the link after if it all works out good and give some follow up advice for anyone else looking to do this. You saying how the expansion valve are made for different refrigerants i wouldn't want to get an older style original one that is not compatible with r134a do you think these two products are fine.

Expansion valve:
https://www.pelicanparts.com/More_Info/1268300384AINT.htm?pn=126-830-03-84-A-INT&bt=Y&fs=0&SVSVSI=

Dryer:
https://www.pelicanparts.com/More_Info/UR1268300383.htm?pn=UR-126-830-0383&bt=Y&fs=0&SVSVSI=3481

Did you mean to run 2 quarts of solvent through that evaporator or 2 quarts for the flush of the whole system. Also should i flush the compressor while i have it on the bench and before i add new oil into it?