I have a 97 E420 and a/c hasn't worked since I had the car. The weather is starting to finally get warmer and I decided I need to fix this problem. I did the diagnostics and checked the trouble codes through the a/c unit. Measurement #7 which is for refrigerant level was at 0. Had not trouble codes come up. Obvious that my a/c needed recharged. Well I bought some r134a and put 1 can in. I checked the measurement afterwards and it said 1. So the second can I hooked up, I pulled up the measurement for the refrigerant level and it went up to 5 pretty fast but then slowly went down to 1 and I disconnected the can. It is obvious I have a leak somewhere, but I have no idea how to figure out where it is coming from?!?!?!?
Sounds like a pretty massive leak. Take the car to a shop that specializes in A/C work and have them diagnose the leak. Could be a coupling but with the speed yours leaked down I would suspect a component like perhaps condensor, compressor, etc. I would also install a new evaporator drier after the leak is repaired. I will caution you about using the DIY cans without checking the pressures as you can overfill or underfill the system and do some damage. You must have a set of gages and know how to use them.
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Bring it to a pro. This is clearly a big problem. The drier on your car is going to be more then fried after all this exposure to air. There is a big leak somewhere if it is leaking out within a couple of minutes! That is really, really bad. The worst I've seen leaked out within a few days, not a few minutes!
While you will definitely need a pro at some point, if you want to diagnose and do the initial repair you can use dye as Matt L suggested. It uses R134a as a carrier so just put a can in with another can of R134a, then engage the system and look for the dye. If it won't hold any pressure it's more likely a blown seal, split hose or a cracked connection (sometimes people inadvertently lean on them or pry against them when doing other work) but the dye will help you isolate it.
Once you find the leak, you can then decide if you want to do the repair. Once the repair is completed, then take it and have them evacuate the system (they'll pull vacuum on it for a period of time to ensure moisture is out of it), replace the dryer (it is probably saturated, but you can ask them, if they don't get lots of moisture out it might be salvageable) and then recharge the system and top up with oil.
Take care and enjoy the ride,
Greg
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Did you add the freon with engine running, or not?
Raising the pressure during filling and than dropping it slowly after is normal occurrence. What pressure is the system showing now?
With a leak that large you should be able to find it while filling. Suggest you trace out all of the lines from the compressor to condenser to filter/drier to expansion valve and then from expansion valve back to compressor. You should be able to see, hear, feel the leak. If nothing in this area, then it could be the evaporator. Ugh!
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