Yes, a 1999 Ford F-250 has a heater relay, though it might not be a single, dedicated relay solely for the heater. The system is more complex than that. The heater motor itself is controlled by a control module that uses relays (possibly several) to switch the power for the blower motor and potentially other heater components (like the grid heater for diesel models). There isn't a single relay simply labeled "Heater Relay."
You'll likely find the relevant relays in the underhood fuse box or a separate relay center. To be certain which relays control the heater blower motor or other heater functions, you'll need to consult a wiring diagram specific to your 1999 Ford F-250's engine and options. These diagrams are often found in a repair manual (Haynes or Chilton) or online through automotive repair databases (like Mitchell 1 or Alldata).
