I recently discovered that the central air in the home I just moved into isn't working. The digital control panel says everything is working perfectly but the system won't start. I went out to the outdoor unit and found the fuses are all operating and power is fine. The contactor is fine as engaging it starts the outdoor unit. The issue is that there were several wires that had their connectors removed haphazardly, I believe these are called female quick disconnects. I also discovered that the anti-short cycle time is partially melted. I believe the removed wire came from this unit to the board and thus the control panel inside. I am going to a HVAC supply shop that the local electrical supply shop guy advised me to try in order to find a replacement. I already know that the timer in the unit is no longer produced. I don't know which wires go where, the diagram has been weathered. I also would like help figuring out what timer to get.

My old (2 ton) unit compressor fried last summer. A friend has a 3 ton that he isn't using. My upstairs is about 1500 sq feet. Downstairs is always cool so I keep the vents shut. I know nothing regarding ac units, so I apologize in advance for dumb questions. Can I switch out to the 3 ton unit for my house? Is it an electrical issue I need to find out about / deal with, or is it just not doable? Thanks in advance.