An HVAC system with a refrigerant gas sensor is provided. In one embodiment, an HVAC system includes a heat exchanger coil installed within a housing. The heat exchanger coil is operable to exchange heat with air in the housing via a refrigerant passing through the heat exchanger coil. The system also includes an HVAC sensor assembly having a refrigerant gas sensor and a processor installed in a sensor housing. The processor is configured to execute stored instructions to identify an undesirable condition pertaining to the refrigerant gas sensor. The HVAC system may also include a controller to prevent an operation of the HVAC system in response to identification of the undesirable condition pertaining to the refrigerant gas sensor. Additional systems, devices, and methods are also disclosed.