can i replace a central air unit myself? i have done much plumbing work (sweating pipe)

the unit is old and needs to be replaced soon. i can buy a new unit at cost, but being strapped for money i wanted to replace it myself. i do a lot of remodeling, much plumbing, but have never worked with central air piping, i know your only supposed to use copper tubing, and not staight pipe with fittings. can i replace the unit myself then call a hvac guy to charge up the unit? any help is apprieciated, thanks.