2000 Mercedes Benz CLK430 air conditioner

Are you trying to charge from the small cans? If so, set the can upright in a pot of hot water.

Be sure you're wearing gloves and a face shield. Escaping refrigerant can cause frostbite and blindness.

The system may be full already, then no additional charge will go in. That would suggest there's some other problem. There's no way to know exactly how much charge is in the system unless you recover all of it, then start fresh with a measured amount. When restarting the charging process, the refrigerant goes in on the low side, and you can feel the hoses getting cold. If blockage is suspected in one of the hoses, this is the time to check for it as the refrigerant is going in. The hose or pipe will get unusually cold at the point of the blockage. Frost will likely develop at that spot.

If there is indeed blockage in the system, and the compressor is working, the high side will develop unusually high pressure, and the low side may get drawn low enough for the low-pressure cutout switch to turn off the compressor intermittently.

Can't help you with that. I'm in the middle of Wisconsin where we throw a pound of salt on an ounce of snow. We use air conditioning only in the summer, meaning three days per year!