Chacin, who has headed to Venezuela after the death of his grandmother, is expected to return for Friday's start at Miami.
Pacheco began the year sharing first base with veteran Todd Helton, but was sent down on July 29 after hitting .229 with 10 doubles, one home run and 17 RBIs in 69 games. He saw two Major League games at catcher, but was behind the plate nine times at Colorado Springs. Pacheco spent much of his Minor League time at catcher before playing third and first at the Major League level last season, and the Rockies believe his skills translate well to the position.
"It took me a couple games to feel comfortable, but they've got a good staff down there, and it made it a little easier to get back in the groove of squatting behind the dish," said Pacheco, who hit .315 with one home run, five doubles and six RBIs at Colorado Springs. "The biggest thing is just catching the baseball. That's your main job, to receive it and keep it in front.
"As far as throwing and all that other stuff, that stuff will come."
Wheeler was a Pacific Coast League All-Star at Colorado Springs, where he hit .308 with 29 doubles, 10 home runs and 81 RBIs. He made six Major League appearances April 25-May 5, going 1-for-9 with a double.
Obtained from the D-backs during the offseason, Wheeler said his earlier time in the Majors -- spent mostly as a reserve -- taught him he needed to work on being more aggressive.
"I'm taking a few more risks at the plate," Wheeler said. "Early in the count, I'm letting it fly a little more. It paid off. I have to drive the ball, being a corner position guy. I worked on taking that 'A' swing, as opposed to always thinking, 'line drive to left field.' I was getting into swings, trying to have some fun. I hope it translates."
Thomas Harding is a reporter for MLB.com. Read his blog, Hardball in the Rockies, and follow him on Twitter @harding_at_mlb. This story was not subject to the approval of Major League Baseball or its clubs.