99 Civic EX - A/C inconsistent in blowing cold
 

The Facts: 99 Civic EX 5spd, 150k miles, drives real good with
minimal issues.

Lately, the A/C has not been consistent in blowing cold. Sometimes it
feels pretty good, other times it feels like it's just blowing from
the vent w/o any cooling. It seems to be blowing warm mostly at stop
and go/city driving, but that might be my imagination.

Any idea what causes this? Thanks!