98 Blazer s 10 heat only comes through vent no matter where I turn switch?

 

What vent is it? Does regular air come out of all the other vents if you set it to them?
It almost sounds like one of your vents is plugged. That or it's a problem with the blower.

 

Automatic Climate Control or Manual?

 

Check your transfer case vacuum switch. The rubber diaphragm fails on these and sucks ATF into the vaccumm lines. I had the same issue with my 02. I changed the switch. The problem is still there but is slightly better. I even went so far as to tear apart the dash and trace all vaccumm lines to check for contamination. I usually close off all front facing vents when I need to defrost the windshield forcing more air to the front. There are a multitude of failure points on this system. Horrible design on the Blazer if you ask me.

 

And it is Manual (i think i haft to turn the ***)
Well like when i turn the are from low to high that's works then i turn the cold or heat that works. But no matter where i turn where i want the air to blow, it comes on and blows out the vents and a lil out of the defrost. So meaning if its on ac max blows out the vents and a lil out of the defrost, if its on defrost it blows out the vents and a lil out of the defrost, exc exc

 

Sounds like your blend door is shot. that would cause air to blow through regardless of setting.
take a peek at this and see if that sounds close

 

It sounds more like the mode door isn't working properly or is stuck...

Here is a schematic showing the HVAC system components:

*schematic for a '01 specifically, but it is very similar to a '98.

And here is the vacuum diagram and logic for your truck:

 

lol im confused...

 

Welcome to the forum and DIY Blazer work

 

I need help where should i start?