Open the coil cabinet and see if the coil is cool, then go outside and put your hands on the 2 copper lines attached to the condenser unit, the large line should be cool (maybe sweating) and the small one should be rather warm. Another quick test is, hold your hand over the condenser fan and see if it is putting out warm air. If these conditions don't exist it is possible you are out of refrigerant. The outdoor condenser coil should be cleaned every year; if it hasn't that would be one thing you can do without spending a lot. Caution, service men love to sell refrigerant, "it just needed a little gas" they say. The refrigerant is in liquid form, picks up heat when it evaporates (in the coil), the hot gas goes to the compressor where it is pressurized and the condenser makes it turn to liquid again. Clean first, gas last. (service men hate that)
I can't believe you need another coil this quick; its nothing for them to last 20years or more.