Jimmy air blend motor?

jimmy99sltjimmy99slt Member Posts: 9
edited May 2014 in GMC
i have a 99 gmc jimmy slt 4x4 4dr with computer climate control. it has a tendency to switch back and forth between hot and cold air, like most of these trucks apparently do. i have read about the air blend motor swithing back and forth, and yes i have the tell tale clicking noise from behind the glovebox. the problem i am having is that the only door i have found behind my glove box seems to work fine, along with the buttons that switch it between outside and cabin air beneath the fan setting on the dash. so where is this little evil blend motor? the other vacuum line behind the box? wouldn't flushing the heater core be a waste of time because i have that crap in my radiator as well? oh and who was the genius that decided were to put the switch for the seat heater in this thing?


  • repairdogrepairdog Member Posts: 948
    The electric blend motor is behind the glove box and look up on top of the heater box and it sits flat up there with an electrical connector. 2 srews hold on and the 3rd rear most mount is only a pin and it lifts off that - many non GM shops pull the dash for this and thats not required.

    I flush the heater core by getting 3' lengths of 5/8 and 3/4 heater hose and simply remove the heater lines at the firewall (elevate the ones you pull off so Dex doesn't drain out and cover the dist cap so it stays dry) and then use a garden hose and flush booth ways till clear and free flowing - I only push the garden hose to the end of the heater hose so I don't blow the core. If the core is really clogged its junk and have to pull the dash to get into the box and about 1 $500-600 job all day. Had two 98s done and my 99 - 01 holding in there.

    As for the seat, another quality engineering job by GM - but come on it lasted 5-6 years (ha, ha). Lots of issues on these vehicles.
  • jimmy99sltjimmy99slt Member Posts: 9
    thank you for the help.

    on the heater core flush i think you missed my point though. what good is flushing the core going to to do? as soon as i flush the core won't it just build right back up since that sandy sludge is all through the radiator as well?

    as for the seat, i was complaining about its location because a couple times i have gotten into the truck, and apparently my foot hits the switch on the way in and about 5 minutes into a trip the seat gets extremely hot. the first time it happened i was in a drive thru line, and didn't know where the switch was.
  • jimmy99sltjimmy99slt Member Posts: 9
    oh and by the way, somewhere on here i read a post that said to bend the corner of the glovebox to get to it, but on mine the metal retainer pushes up out of the way.
  • repairdogrepairdog Member Posts: 948
    If the rad tubes are clogged you still may get the heater core to flow. As for the seat I pulled the fuse on mine but it also operates the lumbar so set it right before you take the fuse out and yep - crappy location and not a hard push to turn on - great here in FL!
  • jimmy99sltjimmy99slt Member Posts: 9
    o.k. I'm certain it'll be the last gm i ever buy. I'm hoping someone can help. I haven't heard the clicking noise since I originally posted this. Heater core flows fine, dash button operated door (right) behind glovebox switches fine. The other door (left) will switch when vacuum is applied, but I have no clue what is supposed to cause it to automatically shift. Bypass heater and A.C. will leave icecubes on your nose. Water flows through the heater core, and all you get is hot air all the time, even when turned off. I have had the heater core bypassed, but the other night in the fog i really needed defrosters. It would be nice to be able to choose hot or cold from inside the truck. The local GMC dealer is hopelessy lost, and wants more to fix it than I paid for the truck.
  • chgoblazerchgoblazer Member Posts: 4
    I have a 2000 blazer ( i believe the same )
    Mine blew cold and lukewarm.
    When I set the blower speed and temp, it blew 100 degrees.
    For some reason when I put it on auto and recirculate, it blew hotter.118* degrees.

    Get a cheap temp. gauge fro the auto parts store, looks like a meat thermametor

    There is s temp sensor deep in the middle vent, blow compress air in the vent, not too much pressure. Blow off dirt dust off the sensor.
  • snowlover4u200snowlover4u200 Member Posts: 1
    Is there any esay way to get at the bled motor? I cant seem to get my hands in there to remove it. Any help would be great. Thank you Dan [email protected]
  • trialanderrortrialanderror Member Posts: 1
    I have a 1999 GMC Jimmy.
    I replaced the thermostat and get engine temps of about 190 degrees F. I replaced the radiator last year. What do I need to do to get hot air out of my vents? It started by giving me about 100 degrees F when set at the warmest temp setting. Now I get about 50 degrees F. This is when it is 35 outside. I used to get the clicking behind the glove box. I haven't heard it for a while. Where is the vacuum line I need to check? How do I get to the air blend motor?
    Where should I start addressing the problem.

    Freezing my behind in Michigan. Actually, the heated seat is all I have to keep me from freezing.
  • rbaumgrasrbaumgras Member Posts: 3
    Because the Main Gear in the Blend Motor has cracked and is now not turning the heat/cold door to the Cold position. 3 fixes: Buy a new Blend motor, takes about 5mins to replace. Buy a new Blend Motor Gear, will take about 30mins to fix. Repair current gear with Epoxy, takes about 30mins and 12hrs for the glue to set up strong enough to use it.

    http://wiki.answers.com/Q/Why_would_your_98_GMC_Jimmy_blow_hot_air_even_when_the- - _temperature_gauge_is_set_to_cold

    Hope this helps. Have not checked my Jimmy yet but I have the same problem. Will check it out tomorrow but this sounds like the real fix.
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