no suction on vacuum

[pool user]

Hi,
We are new pool users about 6 months ago and when I put the vacuum in the pool it works for about 4 minutes and then stops sucking. My sight glass on my pool is only about 3/4 full don't know if this is a sign of anything but would appreciate any help. Thanks

[halito]

then i suggest that you get a new vacuum that actually works!