Hello, have a 98 lt blazer with a heat problem. Replaced thermostat, did a coolant flush and also flushed the heater core using a water hose. The heat seems to work for a few seconds when starting the vehicle only, then the air coming out of the vents seems to kick into overdrive and it gets cool.
The air coming out when on heat isnt what comes out when the ac is on, i guess it is about room temp. I checked the ac compressor isnt stuck running or anything.
I think i remember reading a post here saying i could pull a fuse or something and make the heater blow always?
Any help is appreciated!
(Also the hoses coming out of heater core both get warm and there doesnt seem to be a clog in there.)

 

Sounds like the temperature door actuator is not functioning properly once the fan kicks up in speed.

Do you have the automatic climate control?

 

yes it has the automatic climate control
i had previous problems with the ac and i took out the actuator and checked the gears; the big one had a slight crack in it but didnt seem to affect anything, but perhaps the gear has cracked further?
its so strange how the heat works for a few seconds at first until a fan or something kicks in and then the temp. changes.