Hi everyone, I have a 2000 s10 Blazer 4dr LT edition. Recently I've been having some issues with my heat. First it would cycle every 6 secs (approx.) from cold to hot and back to cold then hot. I diagnosed that the blend door actuator was shot. Replaced that and now it just blows semi-warm air all the time no matter what temp I set it to. Could this be the thermostat?? Please help!!

 

Sounds more like air in the system. Set the vehicle up with the front right tire higher than the rest of the vehicle and vent out any air in the system with the engine running. fill as needed and make sure the overflow tank is up to the proper level also and see what happens.

 

Check for a clogged heater core, I just went through this. With engine up to temp, grab a hold of the 2 hoses coming out of the firewall. Both should be hot, if one is cold, it's clogged, flush the core out using a garden hose.