how to keep field mice out of hvac system ducts, have removed 4 from blower fan.

Mice can get into tiny little holes. I have only had one mouse in my truck but I have cats.

A good cat would help,JK Moth balls may help but have odor to them,not as bad as dead rat thoe.

Not much help. These are good size field mice, how are they getting into system.

Thanks to Js08016 - Jim & tennisshoes. Would still like to know their access point, Was able to block their access to engine airfilter cavity with stiff wire mesh pressure fitted at end of fresh air tunnel at fender well. Hoping a similar barrier for for hvac as well !

Again, thank you for your input, and a place to start prevention efforts. Soon as I drop the blower and remove mouse # 5.