Hi,

I have a 1980 240d.

The paperwork I have says that the car's a/c system has been completely rebuilt; vacuumed out, compressor, dryer, etc...
The paperwork also states that oil was added. The only thing that wasn't added was the R12 which 3 cans were included in the sale of the car.

Before I add the R12 I want to make sure there is enough oil in the system so I don't damage the compressor. I could always add the oil but I don't want to over fill the system if it is already in there.

How can I check the oil level without opening up the system, if at all possible.

Unfortunately the system including the compressor would need to be drained and measured to know for sure. If it is still under vacuum since you got it, that would go a long way to chance it and fill IMO. Otherwise you'll have to open it up and pull the compressor.

If it has the GM R4 black round short compressor I'm rather certain there isn't any way to check it without pulling the compressor and dumping it out to measure.

If it has the cinder block York up high on the RF of the engine there is a way by fabricating a dipstick. , try searching on York AC compressor oil level.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

The compressor says AC Delco 9397.

I tried to find information about it online but no luck.

Delco are usually a rotary piston compressor.

Oil levels in refrigeration aren't super critical. Overfilling is much worse than underfilling as it can hydro-lock a piston. The oil is refrigerant-soluble and travels around the loop, so if there's enough present to keep everything coated then that's enough.

If you had a vacuum pump to re-vacuum it I would say just disconnect the pump and give it a flip and it will spit some oil out if it's full. But if the system has to stay sealed, then you're out of luck, not much you can do without opening it to check the oil.

Once you've added the refrigerant and the system is running under pressure, a standard check is to vent a little from the low pressure side and see that there is oil being carried through the system. Aftermarket oil almost always has UV-reactive dye in it, so it's a fluorescent yellow and very obvious.

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1993 300D 2.5L Turbo

You will need to evacuate the system and see that it holds vacuum, before you add the refrigerant. Once you have the system working you can do as EVRanch said, squirt a bit out of the low pressure fill valve while the A/C is running, to see if some oil comes out with the refrigerant. Catch it on a white napkin or something. If you see oil you're fine. If not you can buy a can of a few oz of oil in refrigerant that can be added through the low pressure port but I'm not sure if it is still available for R 12.

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'97 E 300 D

All of the o-rings, compressor, dryer, expansion valve, ac manifold seals, ac pressure switch were replaced and an ac flush was performed. The system was also vacuumed. I am just not sure if there is oil in the system.

I have 2 ports.

Is the port that is in the hose that is located higher in the car low pressure? How can you tell what is high and what is low pressure?

"Once you've added the refrigerant and the system is running under pressure, a standard check is to vent a little from the low pressure side and see that there is oil being carried through the system. Aftermarket oil almost always has UV-reactive dye in it, so it's a fluorescent yellow and very obvious."

If it was replaced with mineral oil, is there still a way to tell if the oil is present if it doesn't have dye in it?

Also, what is the best way to vent from the low-pressure port? Do you manually push the valve in while the system is running and keep a paper towel to collect any oil that may be pushed out?

Does the paperwork offer a point-of-contact that you could call to confirm 1.) that it was oiled and 2.) what oil was used and what refrigerants are compatible with that oil?

After assembly an AC system should be leak tested with pressure vs. a vacuum. Properly operating AC systems work under pressure, not vacuum. Nitrogen is good for doing a leak test.

After a pressure test and no leaks are found the system should be vacuumed for about an hour to boil out all moisture and then the refrigerant charge should be measured into a vessel and introduced over the vacuum. After the measured refrigerant is in, the system should be checked with gauges to confirm it is properly charged.

To KNOW the amount of oil in the compressor it has to be removed, drained and the oil drained is then measured. The compressor then has to be put on a bench with the ports facing up, the correct amount of oil added and then the compressor input shaft rotated about 10 times by hand.

If I had to guess it probably has the correct amount of oil in it BUT what type of oil? Most technicians know how to add oil and it needs to be done before the compressor is mounted if you want to KNOW the amount inside.

For most, not all DIY situations the pressure test, vacuum/evacuation and charging system might be better left to a trained AC technician.

The smaller diameter lines are the high pressure side, the larger diameter lines are the low pressure.

Be cautious, AC work can be dangerous if you aren't familiar with it, refrigerant cans may rupture if the system has a blockage, refrigerant can freeze an eye or cause frostbite. Putting liquid refrigerant vs gaseous into the system whilst running can bend internal compressor valves. Know and understand what you are doing before attempting to charge/fill a system.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

I would recommend you to leave it to the professionals.

1) The port at the bigger diameter tube is low pressure port.
2) The port at the smaller diameter tube is high pressure port.
3) Oil inside can be mineral oil (r12). If it has been converted to r134 then pag or ester oil may have been added by the shop.
4) It is very difficult to replace all the o-rings. Some are not easy to get to and I doubt any ships would attempt to do it.
5) A/C is work is dangerous to the untrained. It is simple to the professionals.
6) I would not worry too much about how much oil in the system. I always put 4-6 oz of ester oil if I install a new compressor. There will always be some oil inside the recv/dryer.

It is not rocket science. A few oz here and there is not going to affect the performance that much.

Good luck.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

I agree with others, if you can't identify the high and low side ports and you don't feel comfortable with the oil you should probably just hire someone to do it. You can damage your system or injure yourself and without the proper tools and gauges you're shooting in the dark. There's no guarantee that "3 cans" is the correct charge even.

In fact if you have "3 cans" of R12 and a way of installing them that doesn't involve a proper gauge set (probably just a low side whip I'm guessing), I can almost guarantee that those cans contain "R12a" which is actually R290/600a hydrocarbon blend. It's compatible with all oils. Personally I prefer this product for low cost and environmental friendliness over real R12, but you should know that it's actually illegal to charge with it in the USA due to some arbitrary regulations.

All my stuff here in Canada is running on straight R290 or HC blends. Superior product IMO but if this sounds like mad scientist talk... you are either in for a lot of learning to do it properly or you should just hire it done.

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1993 300D 2.5L Turbo

Thanks. Is there a way to get my ac compressor to kick on? Right now, it is not coming on at all. I know it possibly because it is low on or does not have refrigerant in it.

There is a low pressure cutout switch that will keep the clutch from engaging. Most refrigeration compressors are not designed to run under prolonged vacuum conditions, they are cooled by refrigerant flow.

Do you just want to make sure it isn't seized? There isn't much else you can learn by forcing it on without refrigerant in the system, as it doesn't have anything to pump.

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1993 300D 2.5L Turbo

How would one introduce refrigeration into the system if the compressor is not coming on, therefore not sucking the refrigerant into the system through the low pressure fitting.

The refrigerant is put in a graduated/measured vessel with a sight glass, the vessels heater is turned on which increases its pressure measured by a gauge on top of the vessel. The valve is opened on the vessel and you watch the refrigerant go into the system, you then know the correct measured amount went into the system.

The car isn't running during this process.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Take it to a HVAC specialist.
I don't mean to be rude, but not understanding the basics of the AC system, risks, your health, safety and operation of your equipment. It's not rocket science, but you can get hurt as well as your equipment not knowing the proper way to charge a system, and if done wrong, will cost more than having a professional do it. If you insist on learning and doing it yourself, then spend the time reading how tos and watching YouTube vids. The information is out there, just make sure you are confident before you tackle it safely.

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)