Where is the thermostat for internal heating on a 1999 ford fiesta zetec engine?

The 1999 Ford Fiesta Zetec doesn't have a thermostat in the traditional sense that you'd adjust for internal cabin heating. The cabin heating is controlled by the heater control valve (often called a blend door actuator) and the climate control system (which includes the fan speed and temperature controls). There isn't a separate thermostat to regulate the *temperature* of the coolant going *to* the heater core. The engine's thermostat controls the overall engine coolant temperature, and some of that coolant flows through the heater core if the heater is turned on.

If your cabin heater isn't working, the problem likely lies within:

* Heater control valve: This valve controls the flow of coolant to the heater core. It might be stuck closed.

* Climate control system: Faulty blower motor, resistors, or controls themselves.

* Coolant level: Low coolant means less to circulate through the heater core.

* Blocked heater core: A build-up of debris can restrict coolant flow.

* Engine thermostat (not directly related to cabin heat, but a necessary component): A faulty engine thermostat can prevent the engine from reaching optimal temperature, impacting the overall heating system's performance.

To find and diagnose the problem, you'll need to consult a repair manual specific to your 1999 Ford Fiesta Zetec or seek professional help from a mechanic.