The expansion valve has nothing to do with the vents but the vacuum line that controls the center vents may have been dislodged while doing the job.
Poke around under there and see what comes up. Otherwise it's either pull the dash to replace the vacuum element or just lock the vents in the open position and be done with it.

__________________
'70 F100 shortbed
'82 Diesel Westy
'83 Euro 300TD
Curtlo Viper
Yeti ARC
Surly long haul trucker