Just bought a rebuilt AC compressor for an 86 300E. I would like to install the compressor and AC refrigerant/oil to the system by myself. Does anyone know how much oil, and refrigerant is needed for an empty system? The system was changed to 134 from R12. With the rebuilt compressor, which has a little oil in it, is it probably PAG? If so, may I mix with ester oil as required for 134? Do I need a new dryer/receiver? Will it hurt if I take the old parts off, and place in the new parts without pulling a vacuum on the system? What will the little air do to the system? May I add the oil to the compressor by pouring it into the holes for the AC lines to make the proper amount of oil when I use the R134/oil cans that have 10 oz. of refrigerant and 2 oz. of oil pre-mixed? Do I need to by-pass any switches during charging? Question two: I have a 94 E320 that idles @ 750 rpm when in gear, but when put in neutral or park, it goes to about 1200 rpm. My brother 96 does not do this, as it stays at 750 rpm.. What is the problem? How do I locate the parts or adjustments as needed? Kind Regards, Geof

To begin with, we need to know WHY you are replacing the compressor? The procedure will be much different depending upon whether the seal was bad, or if it quit pumping or locked up.

If the compressor quit pumping or locked up, you need to COMPLETELY and THOROUGHLY flush the system. This means breaking every connection and flushing, flushing, flushing, flushing and once you're done with that, then flush the system. It would also be best to add a suction side filter.

Do not take a chance on the oil that is in the compressor, unless you are told exactly what it is, pour it out. If you flush the system because of compressor failure, you can pour the correct amount of Ester (assuming 134 of course) into the system, then thoroughly evacuate the system. Since the weather is turning cool, you may have to use heat lamps on the system to get the temperature high enough to boil off the moisture during evacuation.

DEFINITELY replace the filter drier because you will be opening the system. If you are only replacing the compressor because of a leaking seal, you can plug the lines when you remove them to minimize contamination, but still replace the filter drier. Even in this situation, I would recommend thoroughly flushing the system so that there is no oil left behind. This way you can get the correct amount of Ester oil in the system (assuming you are staying with r134.)

I did not notice what part of the country you are in. If you are in a hot climate like Houston, New Orleans or Florida, you should continue returning to R12 and mineral oil after you've flushed the system. R12 can be had for about $29 per can now. Even at this price, R12 is the cheapest major component in the system.

Good luck,
PS: To determine the correct volume of oil, go to www.aircondition.com and then go "Straight to the Board." Post the question with exact make and model and they will post the volume of oil needed by the end of the day.

What is flushing? What do you use to flush with? The compressor had a bad seal, and eventually locked-up. Where do you pour the oil in?

Kind Regards,

Geof

Don't take this the wrong way, but you're asking some pretty basic questions about your a/c system.

I would suggest having the work done for you.

You could really do some major damage to your system if you're not sure what to do.

In particular, you wouldn't want to harm the evaporator, which would drain your bank account.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Don't take this the wrong way, but I have built from the ground up many Lotus racing engines, suspensions, and transmissions in my earlier years for our racing team. I have never worked on AC, as it is not often found in Lotus 41's, Elans, Europa's built for racing. One uses these forums to educate oneself. If one cannot ask basic questions on a subject in a new field, then knowledge is not attainable, and the learning curve dies. It is not that this person is incapable of learning. I think once I have the information, I would be able to make the right choice as to weather I should proceed or not.

Kind Regards,

Geof

Try starting here Geof for some basics.

http://www.ackits.com/

__________________
Jim

Geof, like yourself, I'm an accomplished DIYer that was stymied by a/c systems until I started studying the posts on aircondition.com. LarryBible is a frequent poster on that site.

I agree with Larry that you should disconnect the system and flush all the components that are flushable. You need a source of shop air. Dress the end of the air gun so you can make a seal by pressing it against the openings of the a/c plumbing. I toss some solvent into each component, then blow it out the other end. Repeat this many times. You want to get any crud out that can ruin your new compressor. You also want to get out most of the old oil. You can start with mineral spirits, but you have to finish with lacquer thinner - or better yet - brake cleaner.

Once it's clean, now is a good time to replace all the seals. The dryer must be replaced.

The correct amount of oil should be distributed throughout the system for good startup once you're finished.... a couple ounces here and there... in the condenser, evaporator, receiver/dryer, and about half the oil in the compressor. I don't know what the specs are for capacities, but keep looking.

After charging with oil, button the system back up and pull a vacuum....the longer the better.

Static charge with one can of refrigerant, then start 'er up and finish charging to proper pressures and vent temps.

For further information, you should post on aircondition.com. Also check out acsource.com, ackits.com, and caawparts.com. I buy all my parts by mailorder through these guys. They are better and cheaper than what you can buy locally.

__________________
95 E320 Cabriolet, 140K

Geof,

You should not be offended by Paul's comments. We have had a number of posters here that have asked basic a/c questions that were alarming. The problem with a/c service is that a number of people over the years have been killed or maimed themselves when trying to charge an a/c system through the high side, causing the can to explode. I think Paul's comments were meant for your safety, not to belittle you. We don't want to see or hear of any of our mercedesshop siblings being hurt.

That said, there is a lot more to a/c service than might meet the eye. Also, you will need some tools and equipment that may make it economically impractical to accomplish yourself. If you still want to learn and do for your own personal satisfaction, there is no one here that understands that thinking more than myself.

Since your compressor locked up, you are most definitely dealing with what most a/c people call a "compressor burnout" situation. This requires the complete flushing as I mentioned in the earlier post. This is best accomplished with a flush gun that allows you to pour in solvent, pressurize and then use the blowgun to force the solvent through the component being flushed. Flush each component in both directions. Flush, flush, flush................ Mineral Spirits works for initial flush, followed by brake cleaner or a/c flush which is a treated alcohol solution.

To flush, disconnect ALL components and flush them individually. Each line should be considered a component and be thoroughly flushed along with the condensor, expansion valve and evaporator. You should also test your evaporator for leaks. This is the big achilles heel of the 124 a/c system. It is about a 15 hour job to replace.

You should replace all o-rings upon reassembly, and if you are going to use 134, you need the green o-rings. Use a nylog lubricant on all the o-rings to ensure a good seal.

Replace the filter drier and put everything together after thoroughly flushed and after you have poured out as much oil from the compressor as you can get. Pour the correct amount of Ester oil for 134 or mineral oil should you decide to go back to R12(this is what I would do.) Pour the oil into the compressor. After everything is together, turn the compressor several times by hand so that there is not a huge slug of oil directly in the compressor upon startup.

After the system is completely reassembled, evacuate the system thoroughly and if the weather is cool, you need to heat the components with a heat lamp to boil out the moisture. In the summer time, you typically do not need extra heat to cause adequate boiling. If ANY moisture is left in the system, it will combine with the refrigerant to make an acid. Believe me, with an evaporator that takes 15 hours to replace, you don't want ANY acid in the system. The evaporator is almost always what the acid will eat up first.

After evacuation, let it draw in as much refrigerant as it will take. This should actuate your low pressure switch allowing the compressor to kick in. This means you should not have to short any pressure switches. After start up, you can then complete the charging.

Necessary supplies and equipment to properly carry out the job will be:

Vacuum pump
Manifold gauges
O-ring kit with Nylog lube
Cannister of refrigerant or can tapper and individual refrigerant cans
Flush gun
Flushing agent
Ester or Mineral oil

Additional parts you will need besides the compressor is the filter drier. This is a MUST after opening the system for major work, not to mention the fact that your filter drier is contaminated with junk from the "compressor burnout."

Don't be fooled when you open the system and don't see large particles in all the components. The contamination consists of very fine particles that are not normally seen by the human eye. After a burnout, however, you can be guaranteed that the contamination is there and MUST be removed.

There are some good books on auto a/c. The aircondition.com and ackits.com are excellent sources of such books as well as parts and excellent advice. The guys are really good and patient with all that post.

Feel free to keep posting questions and comments as you progress through the project and we will help you through it.

Good luck,

I don't take your comments the wrong way at all. In fact, I encourage everyone to learn from these forums. I have learned so much on this forum, that some that read my posts may think that I am actually a tech, or have done the job myself. I should probably put the following in my signature:

"I'm not a technician. I just spent the night in a Holiday Inn Express". :p

I have just read several bad stories on this site about people trying to diagnose and fix a/c problems and got way in over their head real quick, and caused several thousand dollars damage.

You are obviously very experienced on working on cars (more so than me) and surely can judge for yourself whether or not you have the ability to do the job.

I wish you the best,

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Thanks for the write up Kestas and Larry - ya'll answered some pretty basic questions that I had been wondering.

__________________
Jim