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heat coming out of vents.

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Old 05-21-2008, 08:51 AM   #1
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heat coming out of vents.

i have a 04 etreme blazer. when the windows are down and its kinda warm outside say around 85 there is heat coming out of the defrost vents and the front dash vents. the controls are off or on cool. i cant figure it out. makes if feel like i left the heater on after a while. any help would be great.
Old 05-21-2008, 09:01 AM   #2
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Re: heat coming out of vents.

When the engine is running and you change the controls do you hear a 2 second hiss?
Check the vacumm line that runs to the climate controls.
Old 05-21-2008, 09:17 AM   #3
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Re: heat coming out of vents.

i do hear that. it seems like its working right.
Old 05-21-2008, 09:39 AM   #4
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Re: heat coming out of vents.

Ok, well Red stands for hot - Blue stand for cold.
Make sure that the heater control valves controling the flow through your heater hose are funtioning,
Old 05-21-2008, 09:43 AM   #5
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Re: heat coming out of vents.

Quote: Originally Posted by Bill Wheats
Ok, well Red stands for hot - Blue stand for cold.
Make sure that the heater control valves controling the flow through your heater hose are funtioning,
There are no control valves for water flow to the heater core.
Old 05-21-2008, 09:47 AM   #6
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Re: heat coming out of vents.

Quote: Originally Posted by Rhotpursuit
There are no control valves for water flow to the heater core.
Wow! so your heater core is on all the time.

Last edited by Bill Wheats; 05-21-2008 at 09:49 AM.
Old 05-21-2008, 10:27 AM   #7
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Re: heat coming out of vents.

yes i know that the blue meens cold and red meens hot. and yes the heater core is on all the time. i was thinking about getting a valve i could just shut the flow down to the core. i used to take the 2 hoses off of the core and put them together and just create a loop. has anyone done this? i dont no how the newer models would react to that
Old 05-21-2008, 10:34 AM   #8
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Re: heat coming out of vents.

I don't have an 04 to look at, but the flow may be needed to cool parts of your engine.
We usually use 1/2" copper plumbing pipe and hi temp plumbing on/off valves. You may want to use 2 valves and a bypass hose to bypass the heater core during the summer but still allow flow.
Good luck.
Old 05-21-2008, 11:19 AM   #9
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Re: heat coming out of vents.

Mine started doing the same thing last week. My ac used to work fine but now heat comes out with the temp turned on cold and no ac. The compressor still kicks on but all i get is really hot heat.
Old 05-21-2008, 11:21 AM   #10
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Re: heat coming out of vents.

Quote: Originally Posted by layitout
yes i know that the blue meens cold and red meens hot. and yes the heater core is on all the time. i was thinking about getting a valve i could just shut the flow down to the core. i used to take the 2 hoses off of the core and put them together and just create a loop. has anyone done this? i dont no how the newer models would react to that
The "loop" would work just fine.

Sounds like your vacuum motor on the temp control door is busted.

Last edited by Yogi; 05-21-2008 at 11:22 AM.
Old 05-21-2008, 11:23 AM   #11
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Re: heat coming out of vents.

o hold up yall. lol my ac works good it moves to all of the set points on the dial says it does. when the ac is not on and i have the windows down it lets the heat out of the dash and defrost vents. the ones right beside the doors is almost as hot as the ones for the windshield. dunno whats causing it? when i turn the ac on it cools the vents off and then starts to work.
Old 05-21-2008, 11:36 AM   #12
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Re: heat coming out of vents.

layitout, I have the same thing going on with my 1999 truck. Except that I find that the heat comes out from the floor vents. My feet get really hot, and if I put my hand by the vent (floor) it feels hot. Even when the controls are set to off and to the cold temp. I find the best way to solve this is to turn my a/c on for a few minutes then turn it off. Thats how I deal with it. My truck runs like crap with a/c on but thats another story.
Like yours, all my settings work properly. No vacuum lines off or anything.

Last edited by brent769; 05-21-2008 at 11:38 AM.
Old 05-21-2008, 11:44 AM   #13
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Re: heat coming out of vents.

sounds like it a common problem of sorts. some one has to know what is causing it.lol must be a chevy thing
Old 05-21-2008, 01:03 PM   #14
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Re: heat coming out of vents.

Something has to be blocking the damper door from moving into the proper position or the valve/actuator assembly isn't working right.

Bill, you know a ton about these trucks and I'm surprised you didn't know that these trucks don't use heater contol valves anymore.
Old 05-21-2008, 02:48 PM   #15
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Re: heat coming out of vents.

Quote: Originally Posted by layitout
o hold up yall. lol my ac works good it moves to all of the set points on the dial says it does. when the ac is not on and i have the windows down it lets the heat out of the dash and defrost vents. the ones right beside the doors is almost as hot as the ones for the windshield. dunno whats causing it? when i turn the ac on it cools the vents off and then starts to work.
OK - If it's like 70* out and the sun is shining, and I turn my selector to vent with the temp all the way to cold, I get warm (not hot) air out of my vents, and I will usually turn on the A/C. If I turn the selector to "Off" I get no hot airflow. We have had the Blazer since new and this is how it always worked, and the '85 Suburban b4 it.

So GM vehicles do heat up the incoming air somewhat on "Vent", but I've never had a problem with unwanted "Hot" air when the system is off. That is why I think that there is something wrong with the dampers.
Old 05-21-2008, 05:10 PM   #16
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Re: heat coming out of vents.

how would i check the dampners? also some times at night when its cool out side with the windows up around 80 or so it lets some fresh air in the vents not hot mind you just so nice cool air. but thats only at night. during the day with the windows down its totally diffrent. i think maybe i will just take the core out of the loop if i cant resolve it soon. also it does the hot stuff when its in the off and cool position on the other selector. its just plane crazy lol thanks for the help so far guys
Old 05-21-2008, 05:29 PM   #17
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Re: heat coming out of vents.

Quote: Originally Posted by layitout
yes i know that the blue meens cold and red meens hot. and yes the heater core is on all the time. i was thinking about getting a valve i could just shut the flow down to the core. i used to take the 2 hoses off of the core and put them together and just create a loop. has anyone done this? i don't no how the newer models would react to that
I did that on my 82 s10 after i broke the heater core taking it out. i recommend using a clamp or something where they meet.
Old 05-21-2008, 08:33 PM   #18
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Re: heat coming out of vents.

http://www.s-10crewcab.com/phpBB2/vi...ht=hot%2Bfloor


try this
Old 05-21-2008, 09:28 PM   #19
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Re: heat coming out of vents.

Where is the blend door located? Mine started doing this the other day after i had my battery disconnected to clear the code for my check engine light. It's starting to get warm and i need to get this fixed. My fan is off and it still comes out hot when im driving. Even when my ac is on all i get is hot air when the dial is on cold.
Old 05-21-2008, 10:39 PM   #20
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Re: heat coming out of vents.

thanks for the link laydout97! I have had my 2001 s10 for 3 months now and I was wondering what the hell was wrong with my truck. I think I'm gonna try that asap. Now if I can just figure out why my heater seems to have gone to crap on me.
Old 05-21-2008, 10:54 PM   #21
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Re: heat coming out of vents.

thats cool as hell i just went out and did that to my 99, have had this problem for quiet a while it got better when i fixed the a/c. Im going on a road trip this fri ill let you guys know if this works or not.
Old 05-21-2008, 11:02 PM   #22
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Re: heat coming out of vents.

Quote: Originally Posted by layitout
o hold up yall. lol my ac works good it moves to all of the set points on the dial says it does. when the ac is not on and i have the windows down it lets the heat out of the dash and defrost vents. the ones right beside the doors is almost as hot as the ones for the windshield. dunno whats causing it? when i turn the ac on it cools the vents off and then starts to work.
change the temp postion and watch the actuator, if it moves and you still get hot air, suspect a porblem with a door and/or seal not sealing off the heater core portion of the distribution box.
Old 05-22-2008, 08:35 AM   #23
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Re: heat coming out of vents.

thanks laydout97 that did the trick. to all thats has been having heat coming in regardless if its top or bottom this mod works. thanks guys
Old 05-24-2008, 03:20 AM   #24
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Re: heat coming out of vents.

just did it and it worked great. thanks.
Old 05-25-2008, 09:19 PM   #25
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Re: heat coming out of vents.

just got back from my trip and it aslo worked great thanks also
Old 05-25-2008, 10:44 PM   #26
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Re: heat coming out of vents.

Good Find!
Old 05-25-2008, 11:16 PM   #27
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Re: heat coming out of vents.

Quote: Originally Posted by MikeInCtown
...Bill, you know a ton about these trucks and I'm surprised you didn't know that these trucks don't use heater contol valves anymore.
Funny. No I don't. That's why I come here for answers.
I'm not that bad at trouble shooting if I have the correct facts. Just a proccess of elimination and common sense.
But thanks.
It's forums like this that have the info provided by people that know. I would have never had found this answer.
Old 05-26-2008, 12:17 PM   #28
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Re: heat coming out of vents.

sweet it never really botherd me that much but i just went and did the little thing on mine lol think this help with fuel economy
Old 05-26-2008, 02:53 PM   #29
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Re: heat coming out of vents.

Question: Do you have to reconnect the gray hose in the winter to use the heater/defroster? Or do you just reconnect if you want warm feet when selector is in off position? In other words, does disconnecting the gray hose totally disable the heat to the heater/defroster?
Old 05-26-2008, 10:32 PM   #30
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Re: heat coming out of vents.

Quote: Originally Posted by Yogi
Question: Do you have to reconnect the gray hose in the winter to use the heater/defroster? Or do you just reconnect if you want warm feet when selector is in off position? In other words, does disconnecting the gray hose totally disable the heat to the heater/defroster?

after reading no it doesent have to be connected for the heat to work, but with the hose connected it sounds like otheres where saying the heat worked "better"
Old 05-31-2008, 11:24 PM   #31
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Re: heat coming out of vents.

betcha the vaccume solenoid that controlls that door is leaky and is the cause of the heat issue, or if the vaccume lines run to the back of your switch maybe the switch is leaky, the electronic control units have a solenoid bank and I bet it gets used for some offline passive ventalation air temp control.
Old 06-17-2008, 10:49 PM   #32
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Re: heat coming out of vents.

I blocked off the grey tube like in the posted link. I still get air blowing on my feet though. Anyone else have the same problem? If Im on the cold setting it blows cold air, and if Im on the hot setting it blows hot air. It fixed the constant blowing heat but now it is blowing air. All my vents seem to work fine too.
thanks.
Old 06-24-2008, 11:19 PM   #33
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Re: heat coming out of vents.

Quote: Originally Posted by brent769
I blocked off the grey tube like in the posted link. I still get air blowing on my feet though. Anyone else have the same problem? If Im on the cold setting it blows cold air, and if Im on the hot setting it blows hot air. It fixed the constant blowing heat but now it is blowing air. All my vents seem to work fine too.
thanks.
Does your truck have the automatic temp contorl (#'s around knob or just the color code?) Do you have vaccume to the system, small black hose on bank of solenoids under dash? Do any of your functions work other than hot/ cold I.E. Recirc?
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