Air Conditioning - Replacement question

My system has been less than efficient for 2 years and it seems it's finally given up the ghost.

Iv'e adjusted the charge several times, trying high, low and ambient charge with no effect. The coils have been cleaned inside an out.

The Outside unit is a Trane (Feb of '89) 4 ton unit with heat pump. The copper shows no sign of sweating and it simply doesn't cool anymore. Although I haven't checked the Run Load Amps on the compressor yet I feel as though this is the end of this unit. My question(s) is this.

1. I can't find my model online and there doesn't appear to be an efficiency rating on any tag I can find inside or out. If its a 10 sear can I replace just the outside unit or do I have to replace the air handler too?

2. Is a compressor replacement an option? If so, is it recommended (keeping in mind that I'm suffering in this econ at $10 an hour and barely making it).

3. Am I maybe missing something? (more info below if you want to read the details

Details:
It's Texas, its HOT and its humid. I rarely set my thermo under 80° but my system stopped being able to keep up 3 days ago. I had a friend over charge it (outside temp: 100° high side 350 low ~83). We also cleaned the inside coils with coil cleaner and water (I can see light through them with a flashlight). I cleaned the outside coils a month ago. After this service I was able to get the house to cool down to 80° but only after dark. The copper inside and out won't sweat at all. It's barely cool to the touch. Today it seems to have given up the ghost. copper is barely cool and not worth running. We dropped the charge to outside temp + 30 (R22 120 high side) and immediately lost even the small coolness that was in the copper lines. The gauges are steady and not bouncing but I fear the 23 year old Trane Compressor is shot.
Again I haven't checked the amp'rge on the Run load because I don't have the tools until tomorrow but I'm assuming this isn't a quick fix.

Any advise is greatly appreciated. Im sure theres more detail I can provide if you need it.

thanks in advance,
J

Is your friend an HVAC tech?

Checking the comp isn't that hard if you have a meter and know how to use it. May just be a bad capacitor.

Replacing the comp is an option, but I would not advise it on a 20yr plus system.

Before condeming the compressor you need to verify superheat and subcooling.

Here's the latest. The "rushing water" sound that the unit outside makes when the heater turns off is now happening when the A/C kicks off. I'm thinking reversing valve but I don't know how to check it. any ideas?


Answers:
Yes friend is a HVAC tech but has only work with apartments and I get the feeling he's a replace it on the apt's tab kinda guy. We replaced the capacitor with no affect.

Sorry, I don't know what superheat and supercooling is but I can say there's no cooling happening now, super or otherwise :-)

Trane energizes the RV in cooling so the rushing water sound may be normal. I think it's time for you to call a pro.