You’ll want to find a production date. This is typically located on a label on the exterior of your unit.
If your system is under five years old, it may still be under warranty. Having said that, warranty terms and conditions vary between manufacturer and installing company.
At Gordon's Service Experts, we can check your warranty state via a system inspection. We also offer HVAC service memberships in Oklahoma City for residential heating and air conditioning systems, regardless of unit age or manufacturer warranty validity.