And yes I did try to find this via search. My 83 300D was retrofitted with 134A and I need to add some to the system. My hopefully simple question is do I charge as a liguid or as a gas, can upside up or upside down. I will be charging with the compressor running as I did put enough in to get the low pressure switch to engage. The system was not completely empty and I am not doing an evacuation and it is blowing cold with the one can of refrigerant + oil that I did put in. Advise greatly appreciated. Thanks Much.

Somebody please help! Today's the only day I can work on the car! I just don't want to kill either me or it. I am using a pressure guage on the low side to be sure I don't over do the charge. THANKS.

The safest way to do this, without using the proper equipment, would be to vapor charge. The can will get cold and slow the process, but this can overcome be submerging the can in a bucket of warm (not hot) water. It’s easy to “slug” the compressor with a liquid on the low side. Your condenser fan should come on during charging. If you have a thermometer to monitor the center vent outlet, charge to the point the outlet temp stops dropping and starts to rise.

The best way to charge 134a systems is by weight and outlet temp.

Edit
After seeing stevebfl’s post, I'm sure it's in reference to the bucket of warm water. A point well taken. Unless you are familiar with the dynamics and pressure temperature relationship of refrigerants, (as the questioner is not) this is not a good idea. You don’t need to use the water at all or you could use water at ambient (or cooler) temperatures and this will work well too. The reason to use the water is only to lessen the amount of time to charge, giving the canned refrigerant a source of thermal energy.

Also be absolutely sure you are connected to the low side, usually the larger diameter fitting on R12 systems and smaller on r134a (if properly retro-fitted). The low side is the line from the evaporator to the compressor.

Steve’s concern for safety is admirable and I should not have mentioned the warm water. Refrigerant can be very dangerous: one drop of liquid refrigerant vaporizing on your eye could cause blindness. Always use safety goggles.

If you wish to work on your own A/C system you should at least know the basics. It would be a good idea to learn by reading or attending a class on air conditioning. We don’t want to save money at the expense of our health.

MBdiesel, Thank you. I recharged per your directions and all seems to be working as hoped. I still have to find the leak but at least I know the basic system is OK. The Interdynamics kit I bought came with a charging hose and a pretty rudimentary guage. I charged until about the middle of the "safe" zone. Nice clod air, don't know for how log but should be easy for an A/C shop to find the leaks. Thanks Much for your reply and advise. I let the can sit sort of near the radiator to warm it up a bit, worked pretty good.

MB Diesel gave VERY GOOD charging instructions.

The only thing I can add is that if you do have significant leak, next time you charge it, put in a can of UV dye. Run it for a week or so, then use a black light to look for the leak. In this process, use the black light on the condensation drain water to see if it is has any uv dye in it. That way you can fix the leak and do away with the problem.

You did not say how long it took for the refrigerant to leak out. If it took several years, this could be a somewhat normal condition. It is not uncommon for a system to leak a few ounces per year. If this is the case, just recharge when the time comes. If it leaks out sooner, you should find the leak and repair it.

Good luck,

Scary stuff.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

My W124 wagon is not keeping up with our 90 degree weather anymore.

My tech had told me that my fittings indicated that my system was retro'd to R134, although there is no sticker that I've found to document this.

I suspect a leak.

I'm tempted to add some R134 before it's all gone.

I was at Target today and was checking out their selection of cans of stuff from Interdynamics.

They have straight R134 for 9.99 a can, and a couple of other products that include sealers and cleaners, which instinct, and previous Mercedesshop.com posts told me to avoid.

They also sell a couple of low side guages, and the 39.99 "death kit" with that has three cans of oil and R134, and a low side guage.

I figure that since my system was already retro'd, the "death" thing might not apply in my case.

I'm not sure how the oil would get into the gas anyway, if one keeps the can upright, but I also don't want to deprive my system of lubricant.

My AC test equipment consists of not much more than my brain at this point, and I'm trying to get the most bang for the buck without getting my tech involved.

My question is, without wanting to flush the whole system and stuff, would you guys be inclined to recharge with straight R134 or use the R134 with oil?

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Bob Roe
Lehigh Valley PA USA
1973 Olds 88, 1972 MB 280SE, 1978 Datsun 280Z, 1971 Ford T-Bird, 1972 Olds 88, 1983 Nissan Sentra, 1985 Sentra, 1973 230.6, 1990 Acura Integra, 1991 Volvo 940GLE wagon, 1983 300SD, 1984 300SD, 1995 Subaru Legacy L wagon, 2002 Mountaineer, 1991 300TE wagon, 2008 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon, all gone... currently
2007 Honda Odyssey Touring, 2014 E350 4matic

Go without oil. It takes a darn big leak to cause enough oil loss to matter. Say, like a hose blowing apart.

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1989 300 SEL that mostly works, but needs TLC

That's kinda what I was thinking, but I just wanted to get some opinions... thanks!

I don't think that the system is totally dry yet, because I do get some cool air at night or when it's not 80F or more.

thanks again, Bob

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Bob Roe
Lehigh Valley PA USA
1973 Olds 88, 1972 MB 280SE, 1978 Datsun 280Z, 1971 Ford T-Bird, 1972 Olds 88, 1983 Nissan Sentra, 1985 Sentra, 1973 230.6, 1990 Acura Integra, 1991 Volvo 940GLE wagon, 1983 300SD, 1984 300SD, 1995 Subaru Legacy L wagon, 2002 Mountaineer, 1991 300TE wagon, 2008 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon, all gone... currently
2007 Honda Odyssey Touring, 2014 E350 4matic

If the compressor is running at all, there's still some refrigerant in the system.

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1989 300 SEL that mostly works, but needs TLC

This forum is awesome.
Without it, I seriously doubt I would have the testicular fortitude to even think of recharging my own AC.
$28 at AutoZone later, I have cold air.
I bought one of their can tapper/guages and a can of straight R-134a, which is on sale for $8.88 right now btw.
With the AC on max with 91 deg F ambient temperature, and a 72 degree dew point, before charging I had 25 psi on the low side.
I slowly added R-134a ...around 35 psi my aux fans kicked on while idling.
I put a little bit more in until I hit 40 psi. Maybe half a 12 oz. can total, if that.
The instructions on the package said to go for 45-55 psi but I remembered people on this forum recommending 25-35 psi as normal, but I'm thinking that the heat increases the low side pressure, so I'm hoping I've hit a happy medium.
Am I close?
I haven't measured the vent output temperature, but it is now palpably cold!!
I must have a slow leak somewhere; it's taken a couple summers for my AC to go marginal.

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Bob Roe
Lehigh Valley PA USA
1973 Olds 88, 1972 MB 280SE, 1978 Datsun 280Z, 1971 Ford T-Bird, 1972 Olds 88, 1983 Nissan Sentra, 1985 Sentra, 1973 230.6, 1990 Acura Integra, 1991 Volvo 940GLE wagon, 1983 300SD, 1984 300SD, 1995 Subaru Legacy L wagon, 2002 Mountaineer, 1991 300TE wagon, 2008 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon, all gone... currently
2007 Honda Odyssey Touring, 2014 E350 4matic

OLD THREAD REVIVED!

I'm tyring to sort out my AC issues as well, after over a decade of ignoring AC in all my cars altogether. In San Francisco, one hardly ever needs AC anyway. What do you guys think of that PAG oil that supposedly can mix with r-12 oil and is compatible with r-134a?

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'82 300TD
'77 6.9
'75 280S
'74 280
'87 Porsche 944 turbo

I've heard of some a/c guys that swear by that stuff. All they keep is PAG oil in their shop for all a/c work.

But I still think it's best to flush the system during any conversion. It makes the system more efficient and I don't relish the thought of having what would then be foreign material in the system after the conversion.

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95 E320 Cabriolet, 159K

The only car in my fleet which uses r-134a is the 300TD; it was converted already when I bought it. The sticker says they used ester oil and 28oz of refrigerant. I hooked up my gauges to the low-side port by the airbox and it read 0psi. I proceeded to add 12oz of 134a, checked the pressure (all this while the car was idling and the AC blowing) and the pressure was 22psi. I added another can of 12oz of 134a and after that the pressure read about 34 psi. I turned off the AC and the gauge reading went up to 55-60 psi. The whole time, the AC was blowing hot air. I turned the car off to let everything cool off and equilibrate, and I'm about to go out now and check it again.

Concerning the oil, when I retrofit our other cars, I will evacuate the whole systems and use PAG oil - I only kept the ester in the 300td because it was already converted and it was working ok when I bought it.

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'82 300TD
'77 6.9
'75 280S
'74 280
'87 Porsche 944 turbo

Those pressures seem normal for the low side. Too bad you don't have the full set of gauges. I wonder if you still need to add more refrigerant. Even though it blows warm, doesn't the line from evaporator to compressor at least get cold?

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95 E320 Cabriolet, 159K