I have a 1997 Chevy blazer 4x4. I have changed the heater core,and thermostats, but I still do not have any heat? The blower motor is working perfectly fine as it is blowing in cold air. I also have switched the hoses from the heater core around to flush the heater core. There is no leaks any where as well as the radiator hoses are hot. I have also replaced the thermostats twice thinking it could be a faulty thermostate from factory… pls. Help i have to drive 4 hrs and it is currently -17 degrees out.
The problem might be with trapped air in the cooling system.
Get the engine up to operating temperature.
While the engine is idling, loosen the upper radiator hose clamp.
Take a small flat bladed screwdriver and insert it in between the upper radiator hose and the neck on the radiator.
Allow the engine to idle until any air is expelled and nothing but coolant comes out.
Remove the screwdriver and tighten the hose clamp.
Catch any spilled coolant and dispose of it properly. If left on the ground, it can sicken and kill any unlucky animal that laps it up.
Is the screwdriver method any better than running the engine with the radiator cap removed, letting air escape via that route?
A common problem with S-10’s is the blend door actuator. It’s on top of the heater box on the passenger side under the dash. Easy to do.
I think I had a similar problem with my Blazer, except the blend door would get stuck the other way - all the way to heat.
I’m thinking blend door as well.