I'm a tech w/certification but little field experience. I have central a/c condensing unit that hasn't been in use for 2 years. No refrigerant in system so I partially charged it. Replaced capacitor. Tested contactor and compressor terminals (got readings of about 1, 3, and 4) and both good. No burnt wires. Fan runs. Compressor NOT hot-only warm from sunshine. Out of 10 times of powering unit up, compressor has come on for maybe 20 seconds and shut down 3 times only. Has internal overload. Everything looks good. What now? It's an old Lennox unit without low pressure switch. None of my tech friends know what to do other than try new compressor.

Did you check compressor capacitor?

Did the compressor loose all of its oil? Have you tried a hard start kit? Is the amp draw of the compressor with in tolerances stated on the condenser label?

What is the model number? Are you sure there are no pressure switches? Even some of the older lennox models had loss of charge switches. Does the contactor stay pulled in?