First comes the disclaimer, as I am not licensed in anything, I do NOT hold a HVAC license, I am just a boss of 2 HVAC guys, so what I said here is complete BS, anyone cares to read please point out if I am wrong, but don't blame if it doesn't work for you.
This summer, got be the hottest and driest summer I ever remember, putting lots of stress in the AC units, we had many discussion on the AC topic, from disconnect to capacitors, from fan motors to compressors, this post will mainly focus on cost of replacement condensing units.
1. what brand?
--> there are only handful of HVAC manufactures, most manufactures offer more than one brands.
there are other less known brands, some are decent, but mostly lowends.
2. What size?
the rule of thumb is, 1 ton per 700 sq ft, but if money is not the issue, I would like to say 1 ton = 500 sq ft, which put less stress into the condenser, may give your condenser longer life.
3. How Much?
maintenanceUSA is a good place to buy, even cheaper than most wholesale houses, but they only carry 3 different brands, I usually go with GoodMan brand, 5 year warranty, no hasstle claims.
2 ton condenser = 400
2 1/2 ton = 450
3 ton = 550
3 1/2 ton = 650
4. Additional install cost?
lineset 25 ft (3/8+5/8) $130, 50 ft $160.
Freon 30lbs jar = $360.
other misc stuffs like wires, disconnect, in-line filters...
5. Labor cost?
this can varies, so far this summer, we already installed 6 condensers. 2 of them are brand new 2 1/2 tons, rest of them are 5-8 year old used from Craigslist...
5.1 simple condenser exchange. its only a 3-4 hour job, materials cost less $100.
5.2 replace lineset + disconnect + condenser, this is a 8 hour job, lineset=$130, disconnect=$40, other cost $100.
5.3 Adapting to old furnace, A-coil, lineset. this is a 2 day job. lineset = $130, A-coil = $150, other costs = $600.
5.4 installing all new ducts + condenser. this house is 1700 sq ft, used 3 ton heat pump + a-coil = $200, used furnace = $40, lineset = $160, ducts( 4 runs, 10 grilles, 1 return) = $700, other costs = $450. this is a 10 day job.