CONTROL SWITCH HEATER

It doesn't have a heater control valve. You might have the heater hoses on backwards. Try switching them.

Most likely the heater control switch has gone bad. If you follow the heater hoses coming from the firewall you will find a junction that at a minimun 2 hoses attach with a vacuum line. That is your heater control switch. If the diapham goes bad in it you lose your heater.

Control switch is bad.

Its located under the dash, just behind the glove compartment. From what I've read, you have to pretty much remove the entire dash to get to it.

my 2000 chevy blazer zr2 4x4 the a/c switch that does 123 and 4,the a/c only works on num 3 setting.ive just replaced the whole a/c sytem and blower relay.it wont work on num 4 at all and when it does it cuts off on its own and then works on setting 3 only?what to do?

Did you check the level of the coolant? do it while it is running............but make sure it is cooled off.

you should check you thermostat first

I own a 200 Chevrolet Blazer and I have it for over 4 years mine does the same thing I actually just noticed my heat getting less. My husband found the best way to fix it and the cheapest way to fix it. He takes the tube off the heater and attaches a water hose to it and flushes out the gunk whatever is blocking the hose and after he does that the heat works great. No cost and if I wanted to I could do it because its so easy. My husband did some searching on the internet and a person that this happens all the time to let me husband know. If you need more info let me know I can ask my husband he isn't home at the moment I so I don't have exact details. Thanks Amy

the heater core inside the dash is leaking, it may get worse and coolant will start to drip on the floor out of the heating outlet

Try to get reference to owner manual of your car. if you don't have any answer to your question, contact the manufacture , he will give you more information. It is simple a small call and they help you .