Compressor Runs, Does Not Cool

I know I'm not providing all the necessary info, but here goes. I have a Carrier residential outdoor unit that is 20 years or so, has worked well until this season. It is about 3.5 tons. I can post the model number for it, as well as model number on the compressor later today, I'm currently at work. The compressor runs, but it seems to be much quieter, so it is running low. I measured 110V from the yellow- blue and 110V from the black-blue terminals, so it is getting voltage. I have a Fluke amp clamp, but didn't think to take the current draw, will do that tonight. I can hear some whistling through the expansion coil, there is some minor circulation going on. The coil is an A-type and was original to the house (1960). It has an old style expansion valve on it (no orifice). The unit always had problems starting against the closed valve (against the hi head pressure I guess they call it) and about 7 years ago I installed a delay timer which I set at 20 minutes, butit would still have problems starting sot I also installed a supco spp6 which seemed to correct the problem. No issues until this season.
Where should I start? I can measure the coil resistances (yellow-blue and black-blue) and the amp draw on each leg if that info is useful. I also have this capacitor tester which goes up to 200uF: http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber90-570 .
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The system is jurassic mix/match.... Its paid its dues, replace it. They don't last forever. Don't forget to replace the duct system so that it matches the new high efficiency system.

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