Mercedes: Air conditioning problems, coolant recovery, ac center

Question
Having a hard time filling my air unit with refrigerant in my '93 Mercedes 300E 2.8 liter.  Now the unit registers 100 psi and I've expelled an entire can of refrigerant but no cold air.  Was working to a degree before the last time I added refrigerant.  Please advise.

Answer
John,
By not knowing your expertise in AC work, I will just have to make some suggestions.. There are several possible reasons. I would suggest taking the vehicle to an independent AC service center and have the system placed on a coolant recovery machine.
The machine will vacuum out the refrigerant and check for vacuum holding, then the correct amount called for by the manufacturer will be added back.
By law, leaks must be repaired before the system can be charge again.. The center will either uses a dye or a freon sniffer to determine where the leak is.
Over time the seals become hard and freon can leak by the drive shaft on the compressor.
If the system has too much or too little freon it will not cool properly. If moisture has developed in the system it can freeze inside the evaporator and restrict the system.
If there is a failure in the compressor, debris can clog the orifice and stop the cooling cycle.
If liquid has been injected in the system on the wrong side the compressor valve can be damaged.

By having a certified AC center place the vehicle on a machine you should be able to get a diagnosis.
Good Luck
Robert