Working on a 560sl AC. Quick background: AC was not working for about 2 years. Decided last month to charge it . It took the charge, and was working well. The other day while highway driving it got extremely cold, and the fan speed started slowing down, almost to a halt. I turned it off, and let it rest. It worked later that same day, and then two days later it was kaput. - no trace of freon in the system. I believe the evaporator froze, and stopped the fan from turning.
I then decided to charge it, and check for leaks. After juping the low pressure switch I was unable to get the compressor to start, so I jumped it with a 12V source, and put 2 cans of freon and dye in the system. Nice and cold for a while. No trace of dye anywhere, but my sniffer (electronic) sensed some at the front of the pump. No trace in the car, and a possible trace near the evaporator.
I solved the electric problem with a new relay, and I also changed the ETR switch while I had the glove box out. Now the compressor engages when the pushbutton is used, like it should.

My question: I have now tried to vacuum the system down, and it won't hold a vacuum for more than 10 minutes, however it did hold the freon for quite a while on the high pressure side, but not on the low pressure side. The vaccum also drops more quickly on the low side.
Since I can't get to the Evaporator, (the 87 560 sl car was built around it), I'm stumped as to what to attack first. Should I go for the compressor- and see if that solves the vacuum leak/freon leak, or try the expansion valve or evaporator before that.
If it holds the high side longer, does it indicate where the leak is?
Is it possible that the faulty relay and ETR caused the compressor to stay on, and freeze over the evaporator, resulting in the compressor seals to be damaged. I'm wondering why I can't locate the leak with the electronic sniffer unless there is a high pressure on the system, but yet under vacuum the system leaks down very quickly. Any suggestions would be appreciated. Wish there was a way to isolate out the evaporator and expansion valve to do a vacuum test on the rest of the system.

It would not be wise troubleshooting to replace the compressor just to see if it is the problem. It is indeed a distinct possibility, but there's no need to shoot in the dark.

Do you have access to nitrogen? If so, put in a couple ounces of refrigerant and then pressurize the system to a couple hundred pounds with nitrogen. If you have CO2/Argon for a MIG welder, you could pressurize with that. With a leak as big as you describe, have the sniffer ready to go as soon as the system is pressurized. Verify the leak before replacing parts.

Hope this helps.

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Did you ever put any leak detection dye in with a charge and see if any was comming out the condensation drains?

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Thanks for the two replies.
Air and Road, no I don't have access to nitrogen or CO2 Argon. I'm working with a vacuum pump and gauges, and UV light and sniffer. Not sure where to get nitrogen.
TX76513, Yes, I did put UV die in with 2 cans refrigerant. The condensation drains were dripping pretty good, and I was unable to find any trace of the UV. I'm stumped on this one. If this leak was in the evaporator, would the sniffer pick up some in the AC vents? I didn't get any trace there. The biggest hit I got was near the clutch of the compressor, but it wasn't much. It did get more noticeable when the evaporator core froze over.

I have a similar situation ,gas disappears after a day of use. I Checked all joints including receiver/ dryer, next suspect was the compressor seal so i removed the the front pulley and checked for telltale oil signs .
Could it be compressor manifold o -rings leaking under dynamic conditions ?

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Air and road - I just called a welding supply and I can get a tank of nitrogen. I think I will try what you mentioned. Perhaps you could give me a little more direction. Would the procedure be to vacuum the system, put in a pound of refrigerant, and then connect the nitrogen tank to the system, with the compressor running? Or would I shut off the car, and use the tank pressure to get it higher? It sounds like the idea is to use a little refrigerant, and the nitrogen is to dry and pressurize the system? I don't think the sniffer can sense nitrogen, right?

Air & road - I just called a welding supply and I can get a tank of nitrogen. I think I will try what you mentioned. Perhaps you could give me a little more direction. Would the procedure be to vacuum the system, put in a pound of refrigerant, and then connect the nitrogen tank to the system, with the compressor running? Or would I shut off the car, and use the tank pressure to get it higher? It sounds like the idea is to use a little refrigerant, and the nitrogen is to dry and pressurize the system? I don't think the sniffer can sense nitrogen, right?

Well its a good thing that the evaporator appears to be OK.(that is a horrible job in your vehicle to replace) The seals on the compressor shaft do wear, the oil is supposed to keep things lubricated but no use or long set up can make that seal dry out.

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00 E420
98 E300 DT
97 E420 Donor Car - NEED PARTS? PM ME!
97 S500
97 E300D
86 Holden Jackaroo Turbo D
86 300SDL
(o\|/o)

If the 560SL is like the 560SEL, there are o-rings galore in that system... SIX on the compressor alone. Three on the low side hose to the compressor with that fuel cooler, one high to condenser, one condenser to dryer, four at the expansion valve, two dryer.

Chances are your 25 year old o-rings are causing your grief. An o-ring kit is about $10 from AC kits and about $5 for the o-ring lube (looks like snot). I suggest this before you go around and around. I had a cracked o-ring on my 560 at the compressor causing my leakage.

At that point I just opted to flush the entire system and start fresh, new dryer too. No telling what oil(s) had been added over the years. I added a good syn compressor oil that is 134A/R12 compatible and my choice of refrigerant. I would go with R12 unless you update the condenser as memory serves that the R107 has a fairly small system.

Hope it helps.

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I'm not a doctor, but I'll have a look.

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Thanks - Never thought that I would hope the compressor is bad. I don't feel like spending the winter taking the dash apart.

I didn't realize there were so many on the compressor. I have the set of o rings. I already changed the drier, and I am working on all the other accessible ones on the engine side of the car. The compressor actually seems a bit weak anyway, so I'm going to do that also, and get it over with. That with the o rings will hopefully solve the problem. Thanks all. Any other suggestions would be welcome - learning as I go here.

Yes, sticking with R12.

Taking the dash out? I am not familiar with the location of the TXV on the R107, but hopefully it does not entail that. Late W126s with that added crash bar are beyond a pain in the ass to R&R.

How do you know the compressor is weak if the system does not hold a charge?

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

I pulled my hair out looking for a small leak on my 300e. Ended up finding the leak at the very bottom of the condenser. No sniffer found it, and the shroud blocked it from the uv light.

The nitrogen test is simple. just add a bit of freon, and fill the rest with nitrogen. You can charge up to 200 psi. (or more ive heard)

The uv leak detector should show up very well at night with a black light.

Good luck.

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Thanks all. As far as knowing it's weak, I did manage to charge the system, and the pressure never got more than 200psi or so, even after running a while. The system held freon for a while, but would not hold a vacuum for more than a few minutes.
Yesterday, I swapped out the compressor with a new Nippondenzo compressor. Those allen head bolts are a real pain to get to, but managed. PB lubricant made easy work of one, but the other refused - spent about 2 hours trying, and ended up using a dremmel to grind the head off. The stud then easily came out, and I replaced with new.
Now the system holds a vacuum! so it seems it was the compressor afterall. There was basically no oil in the pump. The stuff that dripped out was the UV die. Now I know where it went. Anyway, car is back together, waiting to be charged this weekend. I may give the nitrogen a shot just to help remove moisture - thanks for the info.

Only thing I have to figure out is what the schrader valve on the compressor manifold is for, and do I need to do anything with it. I replaced the stem while I had the compressor off, but does the system get vacuum'd there, or filled?