Pets shed. Or they bring in dust and dirt from the outside. All of which get sucked up into your central HVAC unit. Minimize the number of contaminants brought in your pets by keeping them groomed. Brushing pets regularly helps significantly in reducing the amount of pet dander floating through the air inside your home. Frequent vacuuming and keeping long haired pets trimmed will assist in keeping hair count low as well.

Despite your greatest of efforts, hair and dander will always be an ongoing issue, so you'll still need to make sure you change your air filter regularly to keep it running at maximum efficiency. Changing your HVAC filters once a month (when you have shedding pets can help cut down on the risk of repairs needed because the filter will help keep other components inside the unit cleaner for longer, which also improves efficiency. 

To amplify your efforts on keeping hair from floating around, invest in a good air purifier. It's an extra step in filtering hair and dust created by your furry pals.

Dogs are known to tamper with the fins that surround the outdoor unit as well as marking their territory on it, which can lead to corrosion of the coils. You can put a small fence around the unit to protect it from these behaviors.