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HomeOff Topics › 98 GMC jimmy help
02-02-2013 11:20 PM  5 years agoPost 1
ROGER543

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bristol ct usa

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the heater works in my jimmy but now i can't change it from defrost to vent to floor etc. was wondering if the panel itself need replacing or could it be something else???

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02-02-2013 11:29 PM  5 years agoPost 2
Salty

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St. Augustine

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the servo motor for the flapper valve that diverts the air to the different zones is toast

Ask your Doctor if getting off your ass is right for you.

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02-03-2013 01:06 AM  5 years agoPost 3
ROGER543

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bristol ct usa

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can i just change that or do i need to change the whole unit???

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02-03-2013 01:57 AM  5 years agoPost 4
jbiter

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Sebring, FL

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Check the vacuum line coming from that vacuum reservoir mounted on the underside if the hood.

Jeff

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02-03-2013 02:04 PM  5 years agoPost 5
Chuck Bole

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Tulsa Ok. U.S.A.

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Don't have a GMC Jimmy but i do have a 98 Chevy K1500. Should be the same set up. Mine did the same thing, had to replace the blend door actuator. On the side of the heater/AC box under the dash. The actuator bolts on with 2 or 3 bolts and has two spring loaded arms that attach it to the blend door levers.
Here is the part..
http://www.oreillyauto.com/site/c/d...d+door+actuator

chuck

Team Synergy Field Representative / Thunder Power

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02-03-2013 05:00 PM  5 years agoPost 6
ROGER543

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bristol ct usa

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thanks that the info i needed

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02-03-2013 09:26 PM  5 years agoPost 7
Toadster25

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Iowa

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I have a 2000 blazer and your mode doors are controlled by vacuum. There is most likely a problem with the vacuum getting to the control switch. Either the line has a crack or broke, maybe just fell off but there is another possibility and this is what happened to mine. There is a vacuum switch that goes down to the transfer case so when you engage the 4wd it applies vacuum to a servo that pulls a cable that is connected to the front differential to engage it after the transfer case is locked in. What goes wrong is the vacuum switch leaks and then the fluid in the transfer case gets sucked up into the vacuum lines and all the way into your HVAC controls and can mess things up and block the vacuum from flowing to the vacuum actuators. A lot of times the reason the vacuum switch fails and lets the fluid into the vacuum lines is because the input seal to the transfer case goes bad and let's the transmission fluid into the transfer case and over fills it. I had to replace the input seal and clean all the fluid from the vacuum lines.

Check your transmission fluid level and if it is low with no external leaks I would bet that your transmission fluid has leaked into your transfer case and it is way overfilled and leaking into the vacuum lines. You can also find the vacuum line and pull it apart and see if it looks like there is tranny fluid in it.

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02-03-2013 09:35 PM  5 years agoPost 8
Toadster25

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Iowa

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One more thing my blazer has manual HVAC and not sure if yours is auto or if that makes a difference in how the doors are controlled? I don't think it makes a difference but the auto HVAC might be controlled electrically instead of vacuum like mine.

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02-03-2013 10:46 PM  5 years agoPost 9
ROGER543

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bristol ct usa

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but if it was vacuum control then how come with the engine not running you can still change from vent to floor to defrost? Went and found some vacuum lines going to the heater and so far it all looks good. I just turned 200000 miles so i am expecting to start putting money into it. Right now i will look into the heater blend door actuator and see where this leads me, just trying the cheapest fixes first.

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02-03-2013 11:00 PM  5 years agoPost 10
Chuck Bole

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Tulsa Ok. U.S.A.

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There is a bunch of videos on youtube about this problem but i couldn't find your exact vehicle.

Team Synergy Field Representative / Thunder Power

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02-04-2013 04:42 AM  5 years agoPost 11
Toadster25

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Iowa

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The blend door is electric but that is for changing the temp- hot to cold. The modes are changed with vacuum. You could just take the control panel out of the dash and you will see vacuum lines. Unplug them and see if any of them have vacuum while the engine is running and also watch for the transmission fluid in them. I seriously bet that's your problem but I have seen the rubber vacuum lines at the intake manifold rot out and collapse under the vacuum or split/crack.

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02-04-2013 11:27 AM  5 years agoPost 12
ROGER543

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bristol ct usa

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thanks. just ordered the work manual for it hopefully it will show me where all these hoses are and where to look for it. Just waiting for warmer weather to get in to it

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