Carpenter, who pitched in the Arizona Fall League, regularly hit 100 mph last fall. However his readings have been down from that.
He's also pitched at Triple-A Iowa this season and is 3-2 with a 5.63 ERA in the minors.
Johnson, who had been sidelined with back spasms, was in center field for Tuesday night's game against the Milwaukee Brewers.
Johnson was placed on the DL on May 29, retroactive to May 26. He went 0 for 6 in two rehab games with Iowa.
The corresponding moves were sending right-hander Casey Coleman and outfielder Tyler Colvin to Triple-A Iowa. Colvin hit .105 with two homers and eight RBIs in 38 games with the Cubs, and Coleman was 2-4 with a 7.78 ERA in 10 appearances, including eight starts.
Bruce Levine covers baseball for ESPNChicago.com and ESPN 1000. Information from The Associated Press was used in this report.