On my way home from work i noticed that the heater on my 98 blazer was not working right, it would blow hot air out for about 10 seconds then it would blow cold air out for about 5 secs and it did this the whole time on my trip home about half hour any ideas what it could be.

 

sounds like the radiator is low on antifreeze. i would check the radiator for proper lever and check for any signs of a leak around the water pump or radiator.

 

Might be the vent door for the heat control. It is located on the top of the plastic box behind the glove box. It is vacuum operated so you might have a leak in the line to the door or might be fluid from the trans case. There is a switch on the transfer case that is known to suck the fluid up out of the transfer case and into the heater/a-c controls.

This may not be the problem but sounds a lot like it. Since you get both hot and cold for specific periods of time. It indicates a control function of the heating system so it might not be low coolant but you might have a drop in coolant that won't affect the fact that you are going between hot and cold.

 

i checked the power after disconnecting wire harness from fan switch-i have no voltage at all to the switchwhat powers dash fan switchi cant seem to find blower fuse under the dashthanks for any help

 

I doubt that you'll get an answer. None of these posters have been active for some time. Did you notice the dates of the posts?