i have a 2000 blazer, i have been having some very weird problems with my truck blowing warm air. started in april i was driving to work and i noticed i had no heat when i had the dial turned to hot so i "burped" the sytem and still nothing, so i left it for a bit, then the heat all of a sudden came back, it was good for a while and now it comes and goes. the heat will be all good, then all of a sudden i wont have heat again, then it will come back whenever it feels.

DOES ANYONE HAVE ANY IDEA'S, i ahve asked many people and they have no clue.

 

Possibly a plugged heater core? It is pretty easy to flush.

 

if it was plugged i wouldnt have any heat at anytime though correct? like i stated, the heat will be good, then all of a sudden i will have no heat, then maybe a day to a couple weeks later my heat comes back to normal

 

Depends. You won't know until you flush it. If nothing else, it is good preventative maintenance.

Any other symptoms? Could be the temperature control door (electronic).

 

im thinking the heater control valve at this point but not totally sure

 

I have similar problems with my blazer right now, only this last time the heat never came back. Did you end up trying the control valve. I took the input and output hoses off the heater core and could blow water through them, so I'm assuming it is not plugged and still no heat?

 

Heat started working! ... and about two months later stopped. I blew out all the coolant lines and the heat started working, and then one day it just stopped? Would having it professionally flushed be a good idea?

 

Could be a faulty blend door actuator...

 

I had a similar problem i would only have a little heat. my problem was no vac. from engine.

here is a canister that is vacuum fed (a ball under the hood) that may plugged. check vacuum lines from the motor to the canister. It also runs through the fender inside to the control panel

the control panel inside the truck has a rubber boot on it that has vac. hoses as well. check there for leaks. but i think u would here a hiss while driving.

my control panel leaks a little bit but i still got heat. after i got vacuum to it

the blend door i haven't ever done. but it also runs off vacuum. the valve can wear out and not hold vac. but its weird for it to work some times. unless it electrical.

hope this helps.. there is some vac. pic on this forum that are excellent.

 

Like mh86334; sounds allot like the blend door. Check the electrical plug behind glove compartment.