No Heat 1999 Chevy S10

1999 Chevy S10I replaced the thermostat and radiator cap but no heat. why?


Did it have heat before you replaced these parts?

Did you properly bleed the cooling system after replacing these parts?

Is the coolant level full?

First thing to check would be the coolant level in the radiator and overflow. Next, once the engine is brought up to operating temperature check the heater hoses going to the firewall. If both hoses are hot the problem most likely is with the blend door function. This is inside the HVAC box under the dash. If the temperature blend door actuator or the blend door itself is stuck, no heat will be felt.