Heater don't work - 1999 Chevrolet Blazer

Might be a clogged heater core. Could also be a blend door motor Make sure you have antifreeze up to proper level. don-ohio

sounds like it could be a bad flasher and for the fan there is a fan relay i would suggest checkin that out

Broken heater blend door.

The heater blend door actuator is not opening the door.Check for power at the actuator and if you have power at the actuator and its not working then replace the actuator.These actuators are a well known culprit of this problem.You find the actuator behind the glove box it will have a small arm on it that operates the heater blend door.

First I recommend checking that your coolant level is good. Please check this cold so you don't risk getting burned. I have seen too many heater complaints where the coolant level was simply too low to fill the heater core. Next, you should check if the heater control valve is operating. I don't have any GM experience, but heater valves are often the cause of intermittent heater operation in many cars. Good luck!

That's usually a dirty,clogged heater radiator. How's your antifreeze look? If it's dirty,flush the system out.
But to get your heater working........look down on the firewall and you'll see a coupla' heater hoses entering thru that go to your heater radiator. The trick is to flush backwards from the usual flow direstion that trapped the debris in there.
The flow goes from the hose near the thermostat area into the heater radiator and comes out the other hose and returns to the water pump.
Take these hoses loose from the thermostat area and from the water pump,when the car's engine has cooled.
Now take a regular garden hose with a pistol grip nozzle(just the old cheap type) and hold it tightly to the water pump heater hose and force water back thru the heater radiator.VERY IMPORTANT! DON"T get any water in the alternator and don't let any get into the dipstick of the oil or transmission while you flush!!!
Make sure the hose is directed downward where the debris will come out. (you can tie a large white sock onto the end of the hose and you'll see the debris that you flushed out when you turn it inside out)
Now you have an option to funnel some radiator flush down into the heater radiator and let it sit for an hour,and then reflush the heater the same way and then reconnect the hoses.Enjoy! don-ohio (:^)

When you select A/C or Heater, there is a door (vent air flow change) that open and close when making these selections.

Yep! Take the heater hoses loose from the engine(one at water pupm\\mp and other one at thermostat housing area usually). Then take your water hose at your house,with a common old pistol grip nozzle,and spray water back thru the heater hose you took off the water pump side and that will force it back thru the heater core and out the hose you took off the thermostat side.
If you want to see the junk that flies out of it,tie a white rag or old tee shirt onto the end of the hose.You'll be amazed what flies out of there.Reconnect your heater hoses and see how it does.
I always fill the hose full of water so when I reconnect them,they don't have any airlock problem. don-ohio (:^)

Just a stab at it................see if there's a vacuum or electric operated valve in the heater hose lines.Trace it out.The heater hose goes from the thermostat area at intake manifold thru the heater core,and back to water pump area. don-ohio

Blender door not working on heater/AC box.OR.....it's a severely plugged heater core.don-ohio