Heater blowing hot all the time turning control valve switch makes no diferance any solution ford fiesta 1997

First, make sure your coolant level is full. After spending some time looking around you probably have a shut off valve in the engine compartment. See if you can locate 2 black(sometimes red) heater hoses, about 1 1/4 inches in diameter, coming from the firewall on the passenger side. The heater control valve is located inline with the hoses. It turns on and off the flow of hot water through the heater core which radiates heat in your passenger compartment. Check with your parts house to verify this by looking up the control valve.

There is a separate heater core, like a small radiator, which needs hot water running through it, so when the air blows over it, the air gets hot. It sounds like the diverter valve which sends the hot water to this heater core is not working. It could be a problem with the valve itself, or the relay or switch that controls it, or the vacuum line or device that opens the valve when the switch or relay tells it to open.

if your heater fan blows all the time when you turn the switch on, then check the heater control valve under the hood right before the heater core. its inline with your heater hoses going into the heater core. the valve opens one way and closes the other way as you turn the switch from hot to cold.

bad heater control switch or resistor.

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there is a Temperature Door and an Actuator that controls that door. I've also seen the knob crack, so make sure the knob is turning the temp control switch. I hop you didnt replace the core for no heat.

this is a common fault. heater control valve faulty under scuttle pannel how to test .turn heater control switch half way between hot and cold with fan blowing then touch the valve if it is[ pulsing] ticking then faulty 100% sure this is the problem

sounds like heater control valve situated under scullle panel common fault on ka set heater fan switch half way between hot and cold with heater blowing then touch valve if pulsing or clicking noise it is faulty if doesnt solve problem faulty switch

have u allso checked that the water is acually going into the heater , all feel pipes where they go from engine bay to see if they r hot allso might be air lock

The vacuum operated valve in the engine bay is stuck in the open position.
You should be able to find it on the firewall with the heater hoses from the engine connected to it.