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The heater on my 1999 Jimmy is only blowing hot air. I removed the cover and see that there is only vacuum in the hot (red) line. The fan works at all the settings, but there is no cold and no A/C Is there some reason there is no vacuum on the cold (blue) hose?
The atuator (or whatever it's called) seems to open and close something when I try it. Is it possible that the hiose (blue one) is disconnected beloqw the dash somewhere? I havent sourced where it leads to yet?The atuator (or whatever it's called) seems to open and close something when I try it. Is it possible that the hiose (blue one) is disconnected beloqw the dash somewhere? I havent sourced where it leads to yet?
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I like that you were knowledgeable to check both coolant lines tells me you are getting hot coolant through the heater core next thing to check will be the blend door on the inside of your vehicle. The blend door is a door that switches from cold air duct to heater duct depending on what you are using at the time. If it is stuck on the cold air duct you will not get any heat sometimes these doors are vacuum actuated and sometimes they are electrically actuated most the time you are able to see the movement of the motor from inside if you don't see any movement but you hear it move chances are it is the door blend I hope this helps.
check for vacuum leaks. inspect vacuum lines in engine compartment going ito fire wall just under heater hoses. also listen for vacuum leaks behind dash board. it is normal to hear a slight hissing when the mode door selector is moved into differentpositions for a few seconds.
if the knob wont move replace it junk yard may have used part but if it moves and hot air keeps blowing out u may need a servo that opens and closes heater box door under dash i dont think that trucks system works off vacuum but if it does it probably electronic related problem inquire junk/salvage yard about knob and servo for heater box door and problem it may be common and u may get info if he,s a nice guy
Make sure the raditor is full. Don't just check the overflow tank but pull the cap when the engine is cold and make sure the fluid is to the top. If that is good then check vacuum line that controls the flapper that diverts air from airconditioner to heat. My 1999 Dodge 1500 had this problem and it was a cracked vacuum line.
I WAS TOLD IN THE PAST TO GET RID OF THE ORANGE ANTIFREEZE AND PUT IN THE GREEN IN ALL MY VEHICLES CREATES MORE PROBLEMS THE IT CURES THIS IS BY A SHOP I TRUST.I HAVE A 95/98 AND 99 BLAZERS.I HAD PROBLEM WITH VERY LITTLE HEAT AFTER CHANGING THERMOSTAT. HAD TO GET AIR OUT OF LINES BUY RUNNING IT FROM COLD START WITH RADIATOR CAP OFF UNTIL THERMOSTAT OPENED AND LEFT IT RUNNING UNTIL I SAW NO AIR BUBBLES COMING OUT OF RADIATOR SEEMED TO CURE PROBLEM
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