That depends on the vehicle. Give a make, model and year and there'll be enough information to answer the question.
The fuse for the heater is located in the main fusebox to the right of the steering wheel under the dashboard on RHD Models. It depends what your problem is really but Usually faults with the heater model relate to the heater motor resistor located on the actual heater motor itself. On the extreme left underneath the dashboard. Volksland.com
The heater valve is located inside the heater box.
The Toyota Camry block heater is located on the front of the engine block. You can follow the block heater cord to the block heater.
The heater control valve in a Mustang is located within the engine. It is right in the heater's core and where the coolant is located.
The Pontiac G6 block heater is located on the right hand side of the engine. The block heater can be located by following the block heater cord.
The heater coil is located behind the dash board. You will have to remove the dashboard to get at the heater coil
The heater fan is located under the dash on the passenger side
plastic cover for heater motor
Where is heater blower motor on 1996 Benz C220 located?
Where is the heater blower fan located 1996 honda accord?
block heater on a ford diesel is actually not a block heater but an oil heater this heater is located on the back right side of the oil cooler on side of engine under the exhaust manifold a block heater in an engine actually is in the block
just taking a shot in the dark but is that supposed to read where is the heater core really located on the 1996 Pontiac sunfire??if so its located under the dash of the car,towards the floor board behind the heat exchanger box..if you are asking where the heater core relay is ,,well there is no such thing so need to ask where this is.