Change pacman cache location

Edit /etc/pacman.conf

[options]
# The following paths are commented out with their default values listed.
# If you wish to use different paths, uncomment and update the paths.
#RootDir     = /
#DBPath      = /mnt/HDD/Archives/yay
CacheDir    = /mnt/HDD/Archives/yay
#LogFile     = /var/log/pacman.log

Change CacheDir and use a full path, no relative