No heat in car thermastat is good and no heater coil problem

The heating coil is probably getting plugged up. You may have heat at idle or slow speeds, but once you get going, there is not enough coolant going through it to stay warm. Get the system flushed or replace the heating coil.

if no air in the system from internal heater or other places
new thermostat and radiator cap
good firm coolant hoses

old school air bleed
you fill coolant system with motor running
heater on in the car and thermostat open
burp the hoses until bubbles are no more

if still no better
what about these possibles
faulty coolant temp sender
head gasket failed
clogged radiator
cooling fans not spinning fast enough
or not coming on soon enough

blender door actuator, under passenger side of the dash about 6 inches to the left "toward the center console" of the blower motor.

I’m happy to assist further over the phone at https://www.6ya.com/expert/brock_d67526d2a834c47e

are you installing the correct thermostat the right in the head or block
3 thermostats indicate incorrect fitment method
heater hoses run either way as the water is pushed through the heater core by the pump

could be a thermastat or your heater coil; try starting your vehicle aand putting ani freeze while engine is running but still relativley cool, sounds to me there isnt any fluid getting through to the heater coil

Is coolant level full? To check if the heater core is circulating coolant, feel both heater hoses where they enter the firewall-both should be hot when car is at normal operating temperature. If only one is hot, look for a heater valve in the heater line-make sure it is open so the heater core circulates. Not all vehicles have such a valve, in fact, I think most don't have the valve, but you could check. The valve may be cable operated or vacuum operated to open and close. If no valve, and one hose is cold, there may be an air block in the heater core. Crack a line loose to get coolant circulating.
If both hoses are hot, it is probably the doors in the heater case not operating properly. Watch the door actuators when you move heat from cold to hot, and when moving from defrost to another setting. The temperature blend door is probably on the passenger side of heater case. These doors may be cable operated, vacuum operated, or electrical motor operated. If you watch for their operation, you might see or hear the problem with them not opening or closing properly.
Good luck.
If both heater hoses are hot

i wish you luck but is the temp staying in the usual place on the meter... could be as simple as a heater coil. or maybe the electronic control is not changing to flow water to heater core.. check engine light on?: turn heat on off on off on off to try to get it to change flow.. good luck

Check the thermastat or your cooling fan to make sure all is working good. If your engine cant warm up, you will not produce any heat inside the car

Check the operation of the heater control valve. If it doesn't open up no heat. If the cable moves the control on the valve take the valve off and check it manually. The lever may work but the valve still doesn't open.

It could be the heater control valve under the hood or it could be the heater core is plugged up .