my 87 300d ac has been getting warmer of late and i wanted to top up the freon. i have a bunch of r12 cans and the hose to charge the system but on the cans it has instructions to hold the can one way to charge liquid and upside down to charge gas. which way should i be using the r12? also i don't have gauges to check pressure...i have never messed with ac stuff before but i know there are some w/ much exp. should i try this myself of take it to a shop?

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0o==o0

James 4:8

"...let us put aside the blindness of mind of those who can conceive of nothing higher than what is known through the senses"
-Saint Gregory Palamas, ---Discourse on the Holy Transfiguration of Our Lord God and Savior Jesus Christ


Centrally located in North East Central Pa.

Overcharging is as bad as undercharging. Few of us home mechanics have the skills and equipment to do well on ac issues.

Generally speaking, an ac charge is forever unless there is a leak. My Dodge truck still works fine after 15 years and so did my 1988 560SL after 25 years. I think you also have a leak and may need a hose replaced.

The shop may try to sell you an R134 conversion. Don't do it unless all of your components (compressor, dryer, etc.) are shot. I had a conversion done on my 1983 300CD for that reason. It works fine but it was expensive.

The way to do r12 without a gauge is to watch the sight glass and charge until the bubbles disappear or just before to keep from overcharging. You only charge with the can upside down with engine off. This is done to get enough freon in to overcome the low pressure switch so the compressor will run when the engine is started. You TURN THE CAN UPRIGHT BEFORE starting the engine. You would normally do this only when the system is empty or so low that the compressor will not engage. Liquid freon will not compress so if you try this with the compressor on it will bust the case of the compressor. So, with compressor running, only charge with the can in the upright position, shaking the can to help turn the liquid in the can to a gas faster. This way does not get the exact charge in but is enough to get cold air. Or just take it to a a/c service place.

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85 300 SD ~ 115K
82 500 SEC Euro ??K
78 450SL 164K

ok,so if it is still cool-ish,i may only need to do the second step? which would be gas charge w/ engine on? thanks

__________________
0o==o0

James 4:8

"...let us put aside the blindness of mind of those who can conceive of nothing higher than what is known through the senses"
-Saint Gregory Palamas, ---Discourse on the Holy Transfiguration of Our Lord God and Savior Jesus Christ


Centrally located in North East Central Pa.

Yes, with can upright.

__________________
85 300 SD ~ 115K
82 500 SEC Euro ??K
78 450SL 164K

With the can upright, you will introduce vapor into the system.
Upside down, you introduce liquid.

Which way you hold the can depends upon ambient temperature, and distance from the low side charging port to the compressor.

The higher the temp, and the farther the port from the suction side of the compressor, the lower the risk for intrducing a slug of liquid into the compressor.

Now, we all know what happens when you try to compress a substance that will not compress, right?

If you are just using 12oz cans, and charging into the W124 low side port near the forward firewall on the driver's side, then you should have sufficient distance for the relatively small amount (volume) of liquid introduced into the low side to evaporate before being compresed.

When the low side is located close to the compressor, the risk is high, so you'd want to avoid the upside down can trick if the low side port is within a couple of inches of the compressor.

Another trick to get optimum cooling is to watch the low pressure return line temperature. When you have the proper amount of freon in the system, this return line will start to become very cold.

You can also speed the rate of gas injected into the system by warming up the R12 can. Set it on the radiator hose or other hot engine area. Just be carefull to check the can when picking it up. It'll get quite hot once the freon has left the can......

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

so i decided to run the gauntlet of fear and give it a shot (of freon).....i gingerly added about 1.5 14 oz cans of r12 (which took a looooong time) and it is about 50% colder which should last the rest of the ac 'season'....in the process i broke the vacuum nipple for the shut-off valve so that wasn't too good, but thank you all for the help. now i'm again

__________________
0o==o0

James 4:8

"...let us put aside the blindness of mind of those who can conceive of nothing higher than what is known through the senses"
-Saint Gregory Palamas, ---Discourse on the Holy Transfiguration of Our Lord God and Savior Jesus Christ


Centrally located in North East Central Pa.

Forgot to tell you to run the engine at about 1500 rpm or so to speed the freon intake.

__________________
85 300 SD ~ 115K
82 500 SEC Euro ??K
78 450SL 164K