Air Conditioning - How do you know when your compressor is worn out

I have a Trane Executive B7D742A100B0 made in 1985 and it does not seem to be cooling like it used to. I cleaned the coils and all but they were not really dirty to speak of and it did not seem to help out much.

Other than charging it up which means I have to pay for someone to come out, how do I know I really have a worn out unit or someone just trying to make a sale?

What do I need to know or ask him to insure I make the right decision? Should I watch over his shoulder and read the gages or something? Is there a certain test I should ask him to do?

Thanks

Dave

When unit is running feel the copper lines. small line warm or air temp Big line cold and wetat unit. Gauges on the unit will tell you a lot more. Amp draw of the unit when on. Yes you have to call a hvac guy or gal..
ED;)

As far as watching them ask him or her. I know I always let them watch and ask questions.

Believe it or not when a (good) sevice person comes to your house and talks to you, you (unknowingly) tell him what he has to fix and or look for the problem.