If it is older than 10-12 years old you have to replace one of the major components (compressor,condenser, evaporator), it is time to bite the bullet and replace the entire unit, lines, etc.

They just have lines that run from the compressor to each air handler that hang on a wall.

They are looking for a house to purchase, and I agreed to allow them to go month-to-month with a $50/month rent increase and 60 days notice prior to terminating their lease.We had about $1200 in maintenance costs this year, which included a couple HVAC issues (new thermostat and broken compressor) and replacement of the dryer, which we knew was old and was near end-of-life.We probably put in about two hours of time/effort on the house this year.  

If you are looking to save money, just pay them to change the compressor itself inside the condenser.

The problem is individual electric metering.Is it possible to run lines off one compressor  to units in two different apartments and somehow meter them for their individual electric use?

BFH, sawzall, portable table saw, 12" compound sliding chop saw. wet tile saw, multiple drills, pry bars, portable compressor, Every imaginable small hand tool.

yea...i have to say a van is not very manly, but when you pull up to a Wisconsin Home Depot with a light drizzle in March, you will be glad that you can stick 35 sheets of drywall, lumber, nail guns, compressor, tools, etc in the back of your minivan, and its snug as bug in a rug, and out of the elements. 

Unfortunately I don't have an air compressor yet so that's not an option for me.

The air conditioner compressor needed a $7 part and it took about 15 minutes to install and my worker and I replaced all the baseboards in less than 1 hour because we are lightning fast workers.

The compressor had failed and they would need a factory warranty replacement on the whole unit.