New here. Great forum BTW.

Live in 2740 sq ft house in hot ole Tejas. Big living room with vaulted ceiling, rest of house is 8ft ceiling, tons of windows/glass doors. Both heat pump split systems are original mid 1980's Tranes. 1 ton system on small side (500 sq ft) of house doesn't blow cold. Told compressor valves are shot (low side retarded, oil dark). 3 ton system on main side of house blows cold but there is corrosion in the air handler, likely the coil too. Living on borrowed time with this one.

This house was built as a 2 story but the second floor was never finished out, no fixed stairs even, just attic stairs (big reason we bought the house was due to this potential and we haven't finished out the 2nd floor but will soon). It's 1100 sq feet up there, potential 10-12 ft ceiling. The house is laid out in a linear way. If you can imagine the vaulted living room in between the main side and the kids/guest side, upstairs this splits the space with about 300 sq ft above the kids side and 800 sq feet over the kitchen/master side.

I'm thinking the thing to do is connect existing rigid ductwork (in great shape) and run a new 5-6 ton R410a system for the whole downstairs. Then when when we finish out the 2nd floor intsall another HVAC for it. The other obvious thing to do is replace the dead 1 ton with a new complete 2-2.5 ton system which will be for the small side of the house, both up & down, and then do the same on the main side of the house when the 3 ton dies, replace with big new system that will cover both stories main side.

Each AH is on the 2nd floor (behind what are now and will remain walls - no issue here) close to it's respective AR shaft. If one new bigger AH for the entire 1st floor were installed up here, must it be placed equadistant between these existing AR shafts? Or will a longer duct hook up the the secondary be OK? I'd like to have the 5-6 ton AH installed where our big one is now, and any future smaller AH installed in same spot as where the smaller AH is now.

The lines for the 3 ton can be repulled, for greater capacity/R410a. But the 1 ton lines are in a rock facade wall and pulling them out (for future use in future 2nd floor system) is likely impossible. I'd like to avoid running lines on the exterior. I'll consider ductless for the two upstairs spaces but if I went with a ducted, split system, can the existing lines really be purged/cleaned well enough for conversion to R410a? I'm worried about contamination and if we do a new split system it sure makes sense to replace the lines too.

The techs I've spoken with have all been very good, and pricing is essentially the same, just depends on brand, capacity & features. One tech was maybe biased towards sticking with R22 but he may have been selling me what I was asking for. Another said forget it and make the switch, but concedes R22 will be around. Was also told the lines could be cleaned well enough for a switch.

Sorry, I went on a bit. But...

Is the best zoning to seperate up from down?

If we do one big system for downstairs only, can we put the new big AH where the old big AH is? Meaning very close to main AR shaft and pretty far from secondary AR shaft? Should this be a variable system w/ 2nd TStat and vari-controlled plenum?

Can you really get old lines clean? One tech said if you have a true burn out stick with R22.