Hi Everyone! I am new here on the forum .... But am glad to be here and hope to get some help .. and maybe help others.

I have a 98 Blazer, 4 dr 4wh dr 4.3 vortec motor with auto trans.

I have a heater problem.... it blows air out the ac vents ... turn the **** to heat floor or defrost and it will not switch over .... will not blow out heat when you turn the heat up ....

not sure what to even start looking for the problem... any and all help would be appricated ....
thanks
Bob

 

I have seen the control head cause this problem. What i would do is take the control head out and your main supply vacuum to the unit i think is a black line if i recall. you can attach a small piece of vacuum line to the black one and jump from the main vacuum line to the others and you should notice the positions change for each different color. Also the last one that i did was hissing a little when the control head was faulty. if they change position when you jump the lines you need a control head.
As for the the other problem with your heat not blowing out. Does it not Blow anything out the vent when you turn the fan up or does the air coming out not change temperatures?

 

yes it is blowing out air.. but the temp does not change.... it stays cold
i will check out the control **** ... thanks for the reply ..

 

The vacuum-type control units sometimes crack. Be sure all the vacuum lines are hooked up, and the control unit is free of cracks.

My thought is it's a control unit problem, since you can control neither the heat nor the vents.

 

agreed

 

is the **** the control unit that may be cracked,,, or is it the unit that all the vaccum line connect to that may be cracked .... ???????

 

the unit that the vacuum lines plug into

 

Thanks for all the reply's and suggestions .. they have been very helpful...

Bob