Air conditioning purge - PeachParts Mercedes-Benz Forum

patpong22 · #1 09-10-2009, 11:05 AM

I am converting my 84 300DT to 134. I have a new compressor, receiver/dryer, and expansion valve. I also bought a vacuum pump and manifold for servicing.
Do I absolutely have to use compressed air to flush the system? Can I just use the flushing chemical and then suck it clean with the vacuum pump? I don't have an air compressor. I would have to buy one for this job.
Thanks

gmercoleza · #2 09-10-2009, 11:51 AM

Yes, you need to blow with compressed air. The A/C flush chemical "cleans" and degreases, and loosens the particles. But you can't get the particles out unless you blow them out at high velocity. Think about it - how will you remove a tiny speck of dirt from the middle of the evaporator coil without high velocity air?

The vacuuming process is not what you are thinking. It's not like using a vacuum cleaner. You'll be hooking the vac pump up to a sealed system. The function of vacuuming is removal of moisture, but it does absolutely nothing with solids or other dirt particles in the system.

Did your compressor fail? If so, it's even more imperative that you blow out with compressed air to remove any metal particles.

gmercoleza · #3 09-10-2009, 11:52 AM

I just re-read your first post. If you are converting, you definitely need to blow out since you need to remove ALL the old oil which isn't compatible with R134a. I'm sure others will say you're OK as long as you get most of it. But you really should remove it ALL.

gmercoleza · #4 09-10-2009, 11:53 AM

One more thing - you should really only hook up a vac pump to a CLEAN system. You wouldn't want to ruin the pump by sucking up a particle...

#5 09-10-2009, 12:21 PM

These cars are NOT good candidates for conversion to 134. They don't have enough condensor capacity to adequately perform. R12 is what these systems were designed for and these days only costs a little bit more than R134a.

Additionally, converted systems have a very poor track record for reliability. Those who have kept close records on lots of conversions, PROPER conversions, can back up this statement with facts.

gmercoleza · #6 09-10-2009, 12:27 PM

Quote:

Originally Posted by LarryBible

These cars are NOT good candidates for conversion to 134. They don't have enough condensor capacity to adequately perform. R12 is what these systems were designed for and these days only costs a little bit more than R134a.

Additionally, converted systems have a very poor track record for reliability. Those who have kept close records on lots of conversions, PROPER conversions, can back up this statement with facts.

X2

Why not just get R12?

gmercoleza · #7 09-10-2009, 12:30 PM

One more idea. Do you have a shop vac? As long as your flush chemical isn't flammable, I suppose you could put a couple inches of water in the bottom of the shop vac (to serve as a trap) and use it to "suck" out the pipes. Just use your hand to make a seal between the pipes and the vac hose. Just a thought...

patpong22 · #8 09-10-2009, 12:47 PM

I am having trouble finding R12.
If I don't convert, can I still use the same compressor, receiver dryer and expansion valve I just bought?
Is Duracool as good as R12?
I will buy a compressor.
Thanks,
Cliff

gmercoleza · #9 09-10-2009, 01:01 PM

R12 can be bought at NAPA for $30 or so a can. You can get on eBay or Craigslist even cheaper. Last year through Craigslist I bought a case of about 15 cans (12 oz.) from an 80-year old gentleman who had been saving them for his 2 antique cars. I think I gave him $180 for the whole box, which comes out to about $12 per can. Last I checked, AutoZoo was selling R134a for $10 per can. Of course you need the 609 certification to legally buy R12.

I wouldn't go with Duracool when R12 can be had cheap. Do a search here for alternative refrigerants (be careful - the threads get very heated). You will find that your system was designed for R12, so that's the best refrigerant to use in it.

The components you bought should state what refrigerants they are compatible with.

#10 09-10-2009, 01:10 PM

Yes, you can use the same components with 134 or 12. It is the oil that must be compatible with the refrigerant used.

You would be MUCH better served to use R12, but if you must use an alternative refrigerant, make it 134. All the junk refrigerants like Duracool and dozens of others pose numerous problems. If you are interested in details, do a search ,as this subject has been beaten into complete oblivion here at Mercedesshop.

TOPGUN · #11 09-10-2009, 10:34 PM

Stay with R-12. All of the system components are compatible with R-12. You can rent a small compressor at your local rental place. If the new compressor has an unknown oil in it, flush it out with refrigeration mineral oil. Good Luck.

patpong22 · #12 09-12-2009, 11:51 AM

OK, thanks for valuable input. Bought a used shop air compressor $60, got my EPA license $15, ordered 45 oz. of R12 and 32 oz of oil from ebay. Out of town next week but will let you know how it goes when I get it done. Thanks

dhjenkins · #13 09-12-2009, 04:28 PM

For future reference, shop air is "ok", but the best choice is nitrogen, because it is inert. Compressed air contains small amounts of water (which is why the tank as a drain on it), which is bad for your system regardless of which gas you use.

The key to removing all moisture from your system is to pull a deep vacuum for a long time. The longer the vacuum time, the more molecules of water boil off and get sucked out. Most cheap automotive vacuum pumps are single stage and pull a very weak vacuum, which necessitates a very long vacuum time. I use a robinaire dual stage for all of my A/C work and pull down the system for about 30 minutes.

Like others have said, use only 134-a or r-12. There are dozens of refrigerants on the market, but only those two are suitable for automotive use.

Also, if you're going to switch to 134-a, you should replace the original rubber hoses. R-12 molecules are larger and 134-a can 'seep' through the old hoses.

gmercoleza · #14 09-14-2009, 10:41 AM

Quote:

Originally Posted by dhjenkins

For future reference, shop air is "ok", but the best choice is nitrogen, because it is inert.

He is using the shop air to blow out the flushing agent and any solids with high pressure. Are you saying you can accomplish this using nitrogen?