Sounds like you have a good sized refrigerant leak. The hissing sounds are an initial indication of low refrigerant. On the 210 chassis, warm left cold right is a further sign of low refrigerant. You likely still have some refrigerant in the system, but not enough to provide any cooling. In a mild climate like Michigan most folks won't notice degraded performance until about half the refrigerant charge is gone.

Find a mechanic that does a/c and have 'em take a look. If the location of the leak is not obvious, have it charged up and dye added. When it stops working again the dye will have marked the location of the leak.

- JimY