My heater isn't blowing hot

@jeremyrmoya first make sure that the blower works all the time. Next check to make sure that the cooling system is filled with sufficient coolant. Check to make sure that your Blazer heats up to operating temperature. If it does not, your heater will also not have hot air.

Next would be to check to be sure that all modes on your heater operate. If all those are satisfactory, it is possible that you have a blend door actuator problem or a thermostat issue. If your thermostat stays closed you will not get all of the hot water circulate through your heater core.

Once your Blazers engine reaches operating temp (check your temp gauge). Feel the two water hoses (under the hood)going to your heater. (Careful, they could be hot) See if they indeed are hot and if one is cooler then the other or pretty much the same temp. Always make sure you keep your fingers and loose clothing away from any rotating parts and never open the radiator etc. while the engine is hot (running or not; NEVER)

Here is the Chevrolet S 10 Blazer HVAC chapter from a repair manual. That will at least guide you with some of the steps. Not the best scan but hopefully it still works for you.

Let us know what exact year and engine your Blazer is and what you find out about the heat..