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  #1  
Old 10-25-2003, 11:52 AM
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Replacing AC Compressor and Dryer on W126

I am getting ready to replace the AC compressor on my 126 (350 SDL). Sounds as if this is smarter than replacing only the clutch which is squeaking due to bad bearing ... clutch with 70% the price of the new compressor with clutch.

I would appreciate any advice on this application. While I have replaced compressors before I suspect there are a few interesting points that would be extremely useful. My questions at this juncture are:

General Questions
- Anyone had a "squeaking clutch bearing?" Any idea how long it will last once it starts squeaking?
- I have enough R12 left over from the Cold War era to do the job. Does it make sense to do this with the R12 or convert?
- New compressor with new clutch from Phil is $550 or so with another $75 or so for the dryer ... is this better than looking for a used one ... usually it is, just want to check for expert opinions since mine (opinion) isn't
- While non-OEM systems are available, does it make any sense to consider them ... they look to be generic application vice specific to a particular model ... fraught with "issues?"

Specific Questions
- Does a new compressor come with the lubricant in it? Do I need to add more?
- Anything you would recommend to replace at the same time? (I was going to try and replace the bottom gasket on the Injector Pump with the compressor off ... might be able to do it?)
- Do I need to order anything else "just in case?"
- Anything special about pulling a vacuum on the application?
- In the past I have not used any material to seal the threads as I reinstalled lines, etc ... anything changed in this regard or in "technique" over the past years?
- Any "lessons learned" from your experience?

Thank you very much in advance ... I hate doing all this just for the clutch bearing, but doesn't look like there is any choice ... opinions?
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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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  #2  
Old 10-25-2003, 01:38 PM
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Phil is a great guy. The 10P17C brand new w/ clutch for $550 is a bargain. I would call him again and double check the price of the clutch alone, though, as they usually aren't 70% of the price of a new compressor w/ clutch (more like 40% most of the time). Make sure w/ Phil as there may be some miscommunication on this.

The clutch bearing can be replaced by itself if everything else in the system is working well. Here is an article on the 10P15C(little brother to your 10P17C) that shows how to get to it and you can put in a new bearing and thats it.

http://www.pelicanparts.com/techarticles/911_Nippondenso_rebuild/911_Nippondenso_rebuild.htm
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  #3  
Old 10-25-2003, 04:07 PM
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This response will assume we both have exactly the same system.

I would use Nylog thread seal/lubricant just for peace of mind. It's fairly cheap.

The old compressor will likely have less than an ounce of oil in it. It doesn't have a sump. In theory, you should drain, measure, and replace the exact amount that was in the old compressor, with the same type of oil. (i'm not sure what type). The new compressor will not come with oil.

Make sure you use new o-rings. The new parts will not come with them. You will have to get some.

I would stick with R-12. The system was designed for R-12, and will work better with it.

Should be pretty easy, and straighforward.

Jay
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  #4  
Old 12-14-2003, 12:18 PM
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Finally had time to do the replacement.

Getting at the compressor/clutch assemble was easy requiring both below and above activity ... almost a relief to be able to replace on that is simply bolted on with four long bolts firmly connecting the compressor to the block, instead of the previous styles requiring rotation for tensioning the compressor.

Most exasperating was the lack clearance for getting a couple of the bolts out ... finally managed to move other hoses and lines out the way enough to do so.

Took about 2 hours (could shorten to about 30 minutes if I had to do it again).

The new compressor came with a plate covering the inlet and outlet hose connectors to keep the compressor sealed during shipping. The o-rings that sealed the plate looked to be new, so I Nylog'd well and used them. Nice method for connecting the lines to the compressor ... reference older GM systems and god-forbid, Yorks.

I added about 4-5 ounces of synthetic compressor oil. This was a bit more than recommended by some and less than recommended by some. The old compressor had almost no oil in it ... likely in the lines, I assumed, so reasoned I would use a bit less ... would love to hear more on this topic as there appears to be quite a bit of latitude in the quantity of the oil.

Replaced the receiver-dryer and Nylog'd threads and o-rings ... seemed to go together quite easily, including R&R of the switches.

This part took another hour or so ... could shorten to about 15 minutes if had to do it again.

Pulled vacuum on the system with a new MasterCool pump (I had always wanted one, but lacked "rationalization"). I recall replacing a compressor 20 years ago and using an old converted vacuum pump at a military hobby shop that took 45 minutes to pull a poor vacuum ... even though this was the smallest model available, it took about 3 minutes ...let it run for 20 minutes and pulled 31.5" (gauge error?) on the low side ... connected up high side and pulled it to what could be estimated to be about 30" below zero (no negative shown on the high side gauge).

I do need some help with technical questions:
1. How long should the pump run once the vacuum stabilizes?
2. How much vacuum loss should there be over what period of time? (looks like a I lost about 1 inch over 18 hours)
3. Should both high and low side be evacuated or just low side?
4. Can I leave system evacuated, but without R-12 until Spring?
5. When I charge the system, I was going to hook up low and high with gauge set and slowly add two pounds ... what should pressures be for this system as I add further?

Hope this helps anyone else considering doing this - not a hard job ... it is small compensation for the wonderful technical assistance I have received on this site.
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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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  #5  
Old 12-14-2003, 01:09 PM
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George
I will try to answer your questions in the order you asked them.

1. I like to leave the pump on for at least an hour if possible. It will help get out any mosture which may have gotten in the system.

2. Vacuum loss is very hard to determine as the ambiant temp will have an effect on the readings. If it held vacuum for 18 hours, you are good to go.

3. You can use the low, high, or both. It doesn't matter.

4. I would go ahead and recharge the system and run it a little every week or so. If you don't, some of the seals may dry out and leak when you do recharge.

5. There is no way to say what the pressures will be when you recharge as the ambiant temp makes a BIG difference. I would charge by weight and not worry about pressures at this time. I'm not sure what your car holds but if it calls for lets say 36 ozs then put in 3 12oz cans and don't worry about it.

As far as the amount of oil to add, always go with the max, not the min. If it turns out to be 2 ozs low, you may be puting in another compressor. If you go 2 oz over, you will never know it. Just don't put in an excessive amount as cooling will be affected.

If hope this helps.
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  #6  
Old 12-14-2003, 01:25 PM
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Thanks, Paul ... think you answered everything!

I will have to check to see what the total amount of R-12 is supposed to be ... (this used to be a lot easier when R-12 was 79 cents a pound!)

Does anyone have this data on a 10P17C?

Seems like I used to have a refrigeration book that had generic recommended pressures based on ambient temps, etc.

So, do you think the 5 ounces of oil sounds OK?

Thanks mucho!
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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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  #7  
Old 12-14-2003, 02:20 PM
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Location: Cumming Ga.
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There should be a red sticker on your upper radiator support that shows the amount of freon the system holds. I think your car holds 2.9 lbs but I could be wrong. When charging the system be sure to only charge through the low side if the engine is running.
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  #8  
Old 12-14-2003, 08:48 PM
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Thanks, RPM ... noted the sticker ... had forgotten completely about it. Mine is 2.5 pounds (40 oz).

Pulled vacuum for an hour (had evacuated it last night for about 20 minutes and it held within an inch or so after 15 hours).

Charged with three 12 oz cans and got compressor ops after most of second can. So, guess am within 4 oz of recommended amount. Will wait till summer to add, if ops aren't normal.

With ambient temp in 40F range, stabilized after 36 oz at 32 psi low and 150 psi high. Appears to operate fine.

Thanks to all for the help!
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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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  #9  
Old 12-15-2003, 05:11 PM
LarryBible
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I can't believe what I'm reading in this thread.

You DO NOT use any type of synthetic oil in an R12 system. Use MINERAL OIL ONLY.

Secondly it absolutely DOES matter whether you charge through the low or high side. You can charge through both sides initially after pulling the vacuum, but once you start the engine and engage the clutch, CHARGE THROUGH THE LOW SIDE ONLY. Charging through the high side while clutch is engaged can EXPLODE THE CAN IN YOUR FACE.

Third, too much oil in the system is worse than not enough. To quote Steve Brotherton; "Not enough oil wears out compressors while too much oil destroys them."

You now need to discharge the system, break all connections and thoroughly flush EVERYTHING except the compressor. Remove the compressor and dump out as much oil as you can get out then rinse some mineral oil through it.

After that reinstall the compressor and put the correct amount of MINERAL OIL by putting a little of the quantity in several components. That is if it takes six ounces, put two in the compressor, two in the condensor and two in the evaporator.

Seal everything up, THEN pull your vacuum again as you did, then charge the system.

Good luck,
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  #10  
Old 12-15-2003, 06:36 PM
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Hi Larry,

Here's the description of the oil I used:

"BVA Auto 100 (POE) Auto 100 was developed specifically to meet the operating requirements of automotive air conditioners employing R134a as the refrigerant. Highly miscible with this refrigerant allowing rapid return of the lubricant to the compressor even at low operating temperatures. Although recommended for automotive systems Auto 100 also meets the lubrication requirements of a broad spectrum of industrial applications employing positive displacement or dynamic compressors and requiring a lubricant with a nominal viscosity of 100 at 40 degrees Celsius. Auto 100 can also be used with chlorinated refrigerants such as R-12, R-22 and R-505. Auto 100 is also compatible with petroleum-based refrigeration oils making them ideal for use when changing systems to HFC refrigerants.
Auto 100 is blended from high purity polyol esters having excellent miscibility and lubricity. A special proprietary additive package enhances wear protection for both steel-on-steel and steel-on-aluminum surfaces. It is chemically and thermally stable so that systems stay cleaner even under severe operating conditions."

Doing high and low side was discussion on evacuating the system, not charging it.

I put in 4-5 oz (closer to 4 probably).

I value your knowledge ... what is your impression regarding the BVA Auto 100?

I also used some stuff called Nylog ... seems reasonable that it could prevent some small leaks ...

Thanks!
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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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  #11  
Old 12-15-2003, 08:44 PM
LarryBible
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Stephenson,

To begin with, since the system was operating before dismantling, you had lost no oil except for what might have been in the compressor, which in most cases would be a minute quantity. Adding 4 to 5 ounces under such conditions is way too much.

Secondly, PAG oil which is what this stuff is will not circulate properly with R12. It is compatible in the sense that if there is a trace quantity in the system with the Mineral oil it will have little effect.

I know that my recommendations brought a frown to your face to think about all that work, but if you want the system to live, you really need to do it, and replace the filter drier while you're at it.

Best of luck,
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  #12  
Old 12-16-2003, 12:27 AM
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BVA 100 is an ESTER (polyol type), not PAG. It will circulate fine with R12. It's used as a replacement for mineral oil when converting a system from R12 to 134a. It will work fine with either, though.
PAG is an polyalkalene glycol type, not miscible with R12. The only reason to use POE with R12 is if you are re-retrofitting from a previous conversion or aren't sure what you want as a refrigerant and it's already there. Mineral oil is oil of choice with R12; why change?
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Last edited by jbaj007; 12-16-2003 at 12:39 AM.
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  #13  
Old 12-16-2003, 09:39 AM
LarryBible
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Sorry, it is indeed Ester. I scanned the text quickly and saw the 100 weight indicated and assumed that it was Ester. Since only one weight is available with Ester, it is usually not indicated. When the weight IS indicated it usually means PAG.

That said, the common thing you hear is that Ester is "compatible" with R12. By compatible, that means that if there is a small amount in a system it will not hurt anything. To have such a large quantity in an R12 system is not a good thing.

That is not the worst of it however. The problem with the system is that adding 5 ounces to a system that was nearly full of oil has an EXTREMELY overfilled system.

As I quoted from Steve; "too much oil destroys compressors, not enough wears them out."

This system should be thoroughly flushed, filter drier replaced, the correct amount of MINERAL oil added, evacuated and recharged.

Good luck,
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  #14  
Old 12-16-2003, 12:41 PM
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Darn ... and, I was so close!

I dread doing it all over again ... especially, with the cost of R12 and another dryer ... I will not use it till spring ... will evaluate my desire to do it over versus seeing how long I can get the new compressor to work ... I am just tired of working on it now and have a lot of other things to do.

Thanks very much to all the contributors!
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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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  #15  
Old 12-16-2003, 02:52 PM
LarryBible
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Your local auto a/c shop will have a machine to recover your R12 and recycle it for recharging after you've done the flushing. Be honest with him though and let him know that it has Ester oil. He may want to use a separate cylinder from his usual recovery cylinder.

I have two recovery machines, one set up for 12 and one for 134. On my machines the oil is separated from the refrigerant during recovery and I don't think it would hurt anything.

Just be honest with him so he can protect his equipment and keep from contaminating our remaining R12 supply, part of which is what we can recover.

Good luck,
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