It didn't hold a vacuum overnight. I think I got some o-ring goofiness going on. I didn't quite have the correct ones for the lines to and from the Drier, the condenser, and the high side fitting. Is the O-ring for the high side the same size as the low side? I'm going to go to Napa for a bunch more o-rings.

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1980 240d
1999 SL500

How much vacuum did you lose? All of it? Or could it be explained by water boiling off?

Does your gauge set hold a vacuum overnight? I tested mine with the hose ends connected to the blank fittings on the manifold.

You did oil the o-rings, right?

I'm using this:


I'll test the charge machine against a blank fitting to see if it holds a vacuum itself. I oiled the o-rings and the stepped ports are in the right configuration and at the right torque. I think I used a few wrong O-rings in the system or the Auto Air Service Center III doesn't hold a vacuum itself. It does pull a deep vacuum quickly though. Off to napa to match some O-rings before they close, I'll re-do the O-rings everywhere with the right ones and see if it helps. It may just be that the charging station doesn't hold a vacuum, I'll pull a vacuum on it and see if it holds when I get back.

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1980 240d
1999 SL500

Whether there is a leak in your system or in the charge machine, it is good that you found out with an old dryer. I don't know if it is typical to test with the old dryer, but I did so on mine.

I tested the charge machine. Turns out, I was using the charging hoses backwards. I've had the charge machine connected to the car, and it's held the same vacuum for an hour without a budge in the gauge. I put the old O-rings back on the drier to test if it was those that were wrong. I'll put the new ones back on the drier and test again and leave it for an hour. If it holds vacuum, the new drier and new O-rings go on, vacuum for a few hours, then charge.

Went to NAPA, I shouldn't have said my O-rings were for a 1980 Mercedes. He continued to say that the o-rings were "flat", only available from the dealer, and refused to sell me the "wrong" round O-rings. He said that MB's and Jaguars were the same way with proprietary O-rings. I tried to explain it's a GM A/C system, but no luck. Who's right, NAPA guy or me? I thought that there's nothing special about the MB A/C system and it uses industry standard O-rings and fittings. A guy with integrity, not selling parts that won't work. But is he right? NAPA's are closed now so no luck to get more O-rings. I think my pack from Autozoo has all the O-rings I needed.

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1980 240d
1999 SL500

Well, I was using the hoses correctly the first time, the system does not hold a vacuum for more than an half and hour. I can't tell if the charge machine is leaking vacuum or the car. I'm putting the old o-rings back in and see if it's the new ones that are the problem. It could be the stepped ports too maybe. Are the MB O-rings just standard ones? Are they labeled by #2 O-ring, #3, etc, or just MM measurements? The pack I bought at a McParts should have had all of them. Don't really have time to order O-rings, I leave tuesday for college. Am I doing something wrong with the O-rings?

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1980 240d
1999 SL500

One more update. Bought another pack of O-rings and replaced the ones that were fat and in the expansion valve. Valve was in a little crooked. If all else fails, it's the stepped ports that aren't seated right.

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1980 240d
1999 SL500

Can you blank off the charging machine to ensure that it holds vacuum by itself?

After replacing some odd sized O-rings the system has held vacuum for hours. I'm letting it sit overnight with a vacuum to see if the system holds it. I don't see a way to blank off the charging machine, it may be the charging station or the A/C system with the leak and I wouldn't know. On the charge machine it says it the system holds a vacuum for 2-3 minutes than it doesn't leak...

I could try to take off the hose to the low side quickly and see if the system will hold vacuum that way.

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1980 240d
1999 SL500

Derburger, I got my o-rings prepackaged from AH. They are round and green. Not flat.

I think the NAPA guy is wrong...everything about this system is american....had to buy special SAE wrenches for the job.

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

I got the prepackaged rings from AH too. A pack of those and a pack from another McParts worked, I think. The reason they were flat was 28 years of heat and pressure. The guy thought it was an MB/JAGUAR thing, couldn't explain that everything was American on the system. Hopefully the vacuum will hold tonight and I can recharge tomorrow.

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1980 240d
1999 SL500

Good luck! hope you are nice and frosty by this afternoon!

We drove the wagon to IKEA (4 hour round trip) and had to turn the AC waaay down 'cause we were so cold! R12 rocks!

It was nice to have climate control in the car again after 3 Texas summer months without it.

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Craaap, I broke off the refrigerant temp sensor on the drier in another episode of "forgetting rightey tightey lefty loosey" I'll see if the dealer can get me one today. System held a vacuum overnight though, so I did everything right.

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1980 240d
1999 SL500

If you have the type of temp switch that doesn't actually penetrate the drier and make direct contact with the refrigerant, it's not a show stopper. Press on and intall the switch later.

So it's not really a big deal that it's broken? It is the type that doesn't have contact with the refrigerant. No vacuum leaked out when I broke it. I could go without it for a while before a new one arrives?

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1980 240d
1999 SL500