My house has thermostats all over the place. The house has an oil burner and 3 zones of heat. There's a separate AC system with 2 zones ( 2 separate outdoor RUUD systems ) . I have 2 thermostats in my bedroom, and I'd like to replace them with 1. Can 1 thermostat control 2 separate systems, 1 heat and 1 AC?

My house has thermostats all over the place. The house has an oil burner and 3 zones of heat. There's a separate AC system with 2 zones ( 2 separate outdoor RUUD systems ) . I have 2 thermostats in my bedroom, and I'd like to replace them with 1. Can 1 thermostat control 2 separate systems, 1 heat and 1 AC?

Yes they can be combined BUT it will be a challenge for even a regular HVAC service person. It seems like you probably have many 24 volt transformers (at least one per system IE 1 heat and 1 for cooling) that it can get quite complex for a home owner to figure out without causing damage to your system. There are thermostats designed to use two transformers but the 3 zone system for heat will probably take a professional to figure out so it works properly.