HVAC repair or replace?

[Casey Culver]

I'm trying to decide within the next day or so if I should repair or replace the hvac in my rental. Here's all the details...

-Townhome, 2 bed 2.5 bath 1600 sq ft. There are 2 HVAC units, one for upstairs and one for downstairs. The upstairs unit has stopped working.

-I've only owned the place for a month so I don't know HVAC history...intake filters were pathetically dirty

-The place is currently occupied by tenants, their 13 year old son occupies the bedroom upstairs

-it's April in north Alabama, not terribly hot but it is upstairs and temperatures are beginning to rise.

-Both hvac units are 12-13 years old, 1.5 ton Bryant original units that came with the home.

-Condenser fan motor is gone, $150 I can replace myself BUT I'm also low on freon, estimate about 4 pounds of R22. I've been told that the evaporator coil is usually the culprit for freon leaks about 85% of the time, that's a $600-$900 repair plus about $200 in freon. All in all I'm looking at a $950-$1250 repair in a 13 year old unit. One of the hvac guys also mentioned that compressor may fail soon as well because it's not holding pressure quite like it should. 

-I've been quoted $3900 for an Airtemp 1.5 ton system and $4500 for a Rheem 2 ton system. Hvac guy mentioned he thought the airtemp was a solid unit, didn't breakdown any more than other brands. I'm gonna get 2 more quotes today. 

-I don't pay utilities

-Prices on new hvac will likely go up next month, its the off season still

What would you do? Repair or replace? If replace, then replace with cheaper unit? I don't pay utilities in this thing and I'd like to keep costs low, especially since the currently working unit is the same age.