Chevrolet Repair: no heat, flow control valve, automatic climate control

Question
i have a heater question on a full size 94 blazer with a 350 there is anti freeze put in a new thermastat the temp gage shows heat every thing seems to be working fine but there is no heat at all what could it be?

Answer
Hey Shawn,

  If engine temperature is regulating at 195'F and the coolant is full it can only be one of a few things.
  Before you start poking around in the engine compartment make sure that the interior blend air door is moving.  If it has Automatic Climate control put the fan on high and go from cold to hot selection.  You will hear an audible little noise when the door goes full hot and full cold.  You should also be able to hear the air flow change a bit. The automatic temp control systems have a blend door servo motor that fails and will stick on one temperature.  They can sometimes make a buzzing or clicking noise intermittently when getting ready to fail.
 Providing that the ductwork is ok and the blend door is moving then pop the hood and take a look at the heater hoses.  One may have a flow control valve that is used to limit engine coolant to the core when the AC is on.  This valve looks like a Flush T fitting with a vacuum motor on the side of it with a vacuum line from the command switch.  With the engine running grab the inlet and the outlet of the core one at a time to make sure you have hot water flowing to the core.  If either hose is cold you might have a restriction or a pump volume problem.   A bad pump is very rare but engines that have old coolant with a low concentration of glycol can have an impeller that gets very bad electrolysis damaging the pump and lowering the flow at idle.  Raise the engine RPM and see if that increases your heat a bit.

 Try and do some preliminary diagnosis and feel free to ask more questions.