Missing thermostat? 97 Blazer

Temp gauge won't go higher than 150 degrees and only tempid air blows from heater when set to heat. Could it possibly be that my thermostst is missing? I just purchased it second hand. Thanks:banghead:

Amazing what a cooling system flush will do. Poor baby was full of crud. I guess maybe the temp sensor was coated or corroded with junk. :bananadie