System-Dependent devices can only be used on appliances containing how much refrigerant?

System-dependent devices are specifically designed for use on small appliances that contain a limited amount of refrigerant. They operate by relying on the system's low-pressure side to pull the refrigerant into the device for recovery. The correct answer, which states that system-dependent devices can only be used on appliances containing 15 lbs of refrigerant or less, is based on regulatory guidelines established by the EPA. These guidelines define the capacity limits for different types of recovery equipment to ensure safe and effective recovery of refrigerants.

In practice, using system-dependent devices on appliances with more than 15 lbs of refrigerant could pose risks, as these devices are not designed to handle larger volumes safely and effectively. Therefore, their use is limited to systems with a smaller refrigerant charge to provide adequate safety and efficiency during the refrigerant recovery process. The other options imply larger refrigerant amounts that exceed the scope of what system-dependent devices are intended for, which is why they do not align with the regulatory requirements.