Last AC question for my 300TD - PeachParts Mercedes-Benz Forum

NCfriend · #1 06-28-2009, 11:21 PM

thanks to anyone reading yet another AC thread. This is my first on this very confusing issue, especially to us less mechanically-inclined.

My 1981 300TD, with a good R4 compressor, has been filled TWICE

this summer with freeze12 and can of oil from the dealer that sold it to me. After this expense and some extra dye, I finally tracked down what appears to be the only leak = lines right into the compressor.
Went to find those larger metal/rubber o-rings and several parts stores sold me the wrong parts until I took one into NAPA to compare.
More fun adventures; find that the three 8mm bolts holding the compressor bracket are sheared off deep inside the engine block holes. These will be fun to extract

This week a engineer friend with quality tools will help me remove the broken bolts. I will re-attach the compressor correctly, with a new belt.

Now I bagged my lines on day two.
At this point what do I have to do????

Get someone to pull a vacuum? and for how long 1hr or 24hrs?
Do I add oil to the compressor or wait for the recharge? What type of oil?
Is replacing the dryer a must? Does the dryer get its own oil?
Finally the easiest and most affordable recharge: r12 or freeze12?

And do shops fill with real r12 anymore? Everyone wants to convert me to 134....and I do not think they would even do that properly

I know AC questions are not direct and easy, but please do your best

Matt L · #2 06-29-2009, 12:09 AM

Pulling a vacuum without a good vacuum gauge is an exercise in guesswork. And by good vacuum gauge, I do not mean a standard manifold gauge set where there is 1/2mm at most between 29" and 30" Hg on the dial. That one inch of vacuum is 25,000 microns, and you need to get it below 1000 to boil the water out. How are you going to tell? Additionally, if your vacuum pump oil is old, you won't get as good of a vacuum. I've changed vacuum pump oil in the middle of a job for prophylaxis, but with a meter (which I now have), you know for sure.

It took about four hours to evacuate my car. After the first five minutes, the gauge on the manifold set showed 30", but the micron gauge gave me the real story. It was in the tens of thousands at that point.

E150GT · #3 06-29-2009, 12:11 AM

pull a vaccum for an hour and make sure it holds. i dont know anyone here who will still work on r12. they either try to convert or use freeze 12. i chose neither so i rented a vacuum at autozone and bought gauges and hoses at a pawn shop.

NCfriend · #4 06-29-2009, 09:56 AM

Do most agree that pulling a vacuum is essential at this point, even though I may refill with the same Freeze12?
Does the dryer require replacing?

Should I buy oil to add directly to the compressor before re-installing it, and how do you get the lines on right w/o dripping your compressor oil out on your head?

Lastly, without sparking heated debate. This wagon is about to sale as soon as I have cold AC. I do not have my own gauges or vacuum or know any supply of R12, and do not want to convert everything... So I guess Freeze 12 is an OK option?

Matt L · #5 06-29-2009, 10:59 AM

I would not put Freeze 12 into a car that I was about to sell. It will make it impossible for the future owner to get professional AC service on the car. There are not shops that will recover the stuff. I suspect that most of it gets dumped into the atmosphere by owners as it is and never reclaimed.

Freeze-12 is mostly 134a, but contains other refrigerants to help carry the mineral oil. That's why you can run it with the old oil in the system - until those other refrigerants leak out! Then you have no oil migration and your compressor fails as a result.

Stay away from this junk. One more thing, did you add oil with the refrigerant twice? Before you did that, did your remove the old oil? If the answers are yes and no, you almost certainly have too much oil in that system.

johninva · #6 06-29-2009, 11:28 AM

Quote:

Do most agree that pulling a vacuum is essential at this point, even though I may refill with the same Freeze12?
Does the dryer require replacing?

if you open the system, you are going to need to pull a vacuum and replace the drier before recharging

mobetta · #7 06-29-2009, 02:20 PM

since your selling it, and you want air first, I say 2 choices.

1- convert to 134a= full system flush, replace exp valve, drier, orings, add ester oil and have a shop vac and charge it. or get a vac pump and charge it w/ the cans from the mcparts.

or do the same thing and charge it with r12. there are still shops that do r 12 work, you may need to spend an hour on the phone. r 12 is about 4?x more $$ than 134a, so the cost to charge it will be more, you can get a quote per pound on the phone.

DANSMB · #8 06-29-2009, 02:40 PM

I know all the experts are not going to like this but I have been filling my AC systems for most of my 53 years and not following any of the rules. I have always had perfectly functionoing AC in all of my cars and just did another last month (1981 240D with 77 300D engine). I assemble the system then jump the low pressure switch to get the compressor running, now I take a small screwdriver and hold the high side shrader valve open with the engine running, it purges itself and draws a vacuumm, doing this at a high idle for 2 minutes has always worked for me. Now you need a 134 conversion fitting on the low side so you can add 3 cans of 134 ( one with oil). Done!!!!!! The new 134 cans with the built in gauge make it even easier to get the correct amount in. We have 8 cars now and have done this probably 30 times with no problems, no you don't need to change o rings, hoses, pumps or dryers. Good luck.

Dan

#9 06-29-2009, 06:46 PM

Quote:

Originally Posted by DANSMB

I know all the experts are not going to like this but I have been filling my AC systems for most of my 53 years and not following any of the rules. I have always had perfectly functionoing AC in all of my cars and just did another last month (1981 240D with 77 300D engine). I assemble the system then jump the low pressure switch to get the compressor running, now I take a small screwdriver and hold the high side shrader valve open with the engine running, it purges itself and draws a vacuumm, doing this at a high idle for 2 minutes has always worked for me. Now you need a 134 conversion fitting on the low side so you can add 3 cans of 134 ( one with oil). Done!!!!!! The new 134 cans with the built in gauge make it even easier to get the correct amount in. We have 8 cars now and have done this probably 30 times with no problems, no you don't need to change o rings, hoses, pumps or dryers. Good luck.

Dan

Scary stuff!

Cervan · #10 06-30-2009, 05:36 AM

Quote:

Originally Posted by DANSMB

I know all the experts are not going to like this but I have been filling my AC systems for most of my 53 years and not following any of the rules. I have always had perfectly functionoing AC in all of my cars and just did another last month (1981 240D with 77 300D engine). I assemble the system then jump the low pressure switch to get the compressor running, now I take a small screwdriver and hold the high side shrader valve open with the engine running, it purges itself and draws a vacuumm, doing this at a high idle for 2 minutes has always worked for me. Now you need a 134 conversion fitting on the low side so you can add 3 cans of 134 ( one with oil). Done!!!!!! The new 134 cans with the built in gauge make it even easier to get the correct amount in. We have 8 cars now and have done this probably 30 times with no problems, no you don't need to change o rings, hoses, pumps or dryers. Good luck.

Dan

will work, but its not correct.

DANSMB · #11 07-01-2009, 06:54 PM

Quote:

Originally Posted by Cervan

will work, but its not correct.

Yes we all know it’s not correct because we aren’t paying a shop $300 to do it but having cold air for $30? Can’t complain about that. I’m an engineer, licensed A&P mechanic and airline pilot and except for not pulling the vacuum for long enough I can’t see how this method differs from the job the pros do. This isn’t rocket science, all we are doing is pushing fluid thru a small hole which causes it to cool as it expands in the evaporator and magic, we have cool air! You could fill it with any fluid that won’t freeze and it would work, maybe not as efficiently. If you have been driving around without AC because of the high cost to have it serviced then maybe this method is for you.

Dan

tangofox007 · #12 07-01-2009, 07:22 PM

Quote:

Originally Posted by DANSMB

This isn’t rocket science...

It's a lot more like rocket science than a lot of folks realize. Shortcuts negatively affect system longevity to a much greater extent than they affect short term performance. Maybe thats why you have needed to go through the process so many times on your vehicles.

#13 07-01-2009, 08:06 PM

Quote:

Originally Posted by Matt L

Pulling a vacuum without a good vacuum gauge is an exercise in guesswork. And by good vacuum gauge, I do not mean a standard manifold gauge set where there is 1/2mm at most between 29" and 30" Hg on the dial. That one inch of vacuum is 25,000 microns, and you need to get it below 1000 to boil the water out. How are you going to tell? Additionally, if your vacuum pump oil is old, you won't get as good of a vacuum. I've changed vacuum pump oil in the middle of a job for prophylaxis, but with a meter (which I now have), you know for sure.

It took about four hours to evacuate my car. After the first five minutes, the gauge on the manifold set showed 30", but the micron gauge gave me the real story. It was in the tens of thousands at that point.

In the seventies I worked in a Bio Medical Instrument shop in the Biology/Chemistry Department at North Texas State University. We had vacuum gauges as you described and it took a good vacuum pump with fresh oil and in good condition to pull a really good vacuum. I would like to have one of those pumps and one of those gauges.

It is indeed common to just hook up a set of manifold gauges, turn on the pump and see how fast it pegs the meter and the pull for awhile. I expect that the vast majority of auto a/c's are evacuated that way, but a good gauge would indeed remove lots of guess work. I also expect it would provide incentive for frequent pump oil changes.

When we messed with those Scientific type pumps, it was amazing how much more vacuum they would pull after a simple oil change.

DANSMB · #14 07-01-2009, 08:17 PM

Actually I haven’t had to do any of my cars more than once, we have just owned a lot of cars and I have helped many friends fix theirs. The 84 Mustang was done 12 years ago and still works fine. I agree that shortcuts are generally bad and I do take care of my cars and boats with all the scheduled and suggested maintenance. This is one instance where a person can save some dollars if desired. What’s the harm trying? 3 cans of Freon? Obviously I am getting enough of a vacuum to get the moisture out or it would freeze up.

Dan

Matt L · #15 07-02-2009, 01:54 AM

Quote:

Originally Posted by DANSMB

Actually I haven’t had to do any of my cars more than once, we have just owned a lot of cars and I have helped many friends fix theirs. The 84 Mustang was done 12 years ago and still works fine. I agree that shortcuts are generally bad and I do take care of my cars and boats with all the scheduled and suggested maintenance. This is one instance where a person can save some dollars if desired. What’s the harm trying? 3 cans of Freon? Obviously I am getting enough of a vacuum to get the moisture out or it would freeze up.

Dan

You're really sure that there is no difference here between doing it right and otherwise?

You cannot be getting all of the AIR out, since you're forcing it out the high side. Sure the system will work, but it is working harder than it would need to be. That means increased pressure, and increased fuel usage.

And it takes a lot of moisture to create a blockage. It only takes a little to contaminate your oil. I am betting that this Mustang is an anomaly. Does "owned lots of cars" mean that you don't keep them long?