Vents not working

Tiny
JOE THE MARINE
  • MEMBER
  • 2002 CHEVROLET BLAZER
  • 4.3L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 178,000 MILES
Just replace heater core, now where the heat comes out on the floor, it always seems as if hot air is always coming out the vents, both sides of the floor. The switches for the heat is off and I can't figure out way this is doing this, is this some kind of pollution where the air has to come out all the time? The temperature here is in the 60 degree mark, but the floor vent blowing the hot air makes my drivers side foot feel like its on fire. Can you help me on this issue please. Thanks
Saturday, May 2nd, 2020 AT 7:35 AM

42 Replies

Tiny
HARRY P
  • MECHANIC
  • 2,292 POSTS
Hello. If memory serves, there's a vacuum line under the dash, drivers side, nearish to the console. This line gets disconnected when you pull the dashboard back to get to that heater core. Make sure it is connected. Then start the truck and put the HVAC on Max A/C mode and let it run for a minute. Now check to see if there's anything coming from the floor vents. Hopefully this takes care of your problem. I tried to get you a diagram but can't seem to locate one on AllData.

Good luck!
Harry
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Saturday, May 2nd, 2020 AT 2:21 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,080 POSTS
Does moving the mode control do anything? IE put it on defrost it switches to defrost or to the dash it blows out the dash? This is the vacuum line diagram, unfortunately it doesn't show the actual routing of the lines. Your description sounds like the main vacuum line is off but there are a few that can cause problems.
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Thursday, May 7th, 2020 AT 9:40 AM
Tiny
JOE THE MARINE
  • MEMBER
  • 62 POSTS
Did what you said, here I found out the blend door actuator wasn't working, because I had no a/c, after I replaced it, all issues were resolved. Thanks for your help anyway, you led me in the right direction.
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Friday, May 8th, 2020 AT 12:28 PM
Tiny
JOE THE MARINE
  • MEMBER
  • 62 POSTS
Tried to turn on the A/C today, and all I get is hot air coming out the vents. Check for Freon, it's full, the black box is ice cold under the hood. I'm lost on this one. Hope you can help on this issues. Thanks so far.
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Sunday, May 17th, 2020 AT 6:46 AM
Tiny
JOE THE MARINE
  • MEMBER
  • 62 POSTS
Did you get this question I ask you? I didn't get a email conformation to confirm I send in the question. Thanks
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Sunday, May 17th, 2020 AT 8:12 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,080 POSTS
If the HVAC case is cold but you only get hot air the temperature door in the box is stuck on hot. The air travels into the inlet then through the A/C core then hits the temperature door. That directs the air to go either into the cabin or through the heater core and into the cabin. On your truck that door is controlled by an electric servo located on top of the case. To get to it requires the dash be removed so you can get to the top of the case and test or replace the actuator.
What you might try is a re-calibration. Remove the HVAC 1 fuse and keep it out for more than a minute. Now replace it and turn the key to the run position. Now cycle the heat control from hot to cold a couple times and see if you can hear the actuator moving. Or start the truck and see if the air temperature changes now. If it does then it may be okay, if not then more testing will be needed.
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Sunday, May 17th, 2020 AT 3:07 PM
Tiny
JOE THE MARINE
  • MEMBER
  • 62 POSTS
Thanks for the reply, will do. I believe its the blend door myself, and I can get to it through the glove box, I have little hands and time and will have a few beers before I do this. I will keep you updated on this issue. Have a nice day, and thanks for the time on your end.
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Sunday, May 17th, 2020 AT 5:24 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,080 POSTS
Good luck, I've done a few that way but it makes my hands cramp up getting them in there.
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Sunday, May 17th, 2020 AT 5:56 PM
Tiny
JOE THE MARINE
  • MEMBER
  • 62 POSTS
Will work on it today, and keep you updated. Also as of this morning, heat coming from the top vents, oh boy, here we go again. Waiting for the part to arrive from AutoZone, $44.00. Will see if this does the job. Say a pray for me and a few beers, ha ha ha, , bye
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Monday, May 18th, 2020 AT 7:12 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,080 POSTS
JOE THE MARINE, have any luck with the actuator or still waiting for the parts?
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Wednesday, May 20th, 2020 AT 6:37 PM
Tiny
HARRY P
  • MECHANIC
  • 2,292 POSTS
Joe, having had a few of these trucks, I have to say check the control head. I've had a couple of them fail on me, having the temperature stay on whatever it was on when it decided to take a break. If I fought with it by turning the knob up and down repeatedly it would eventually start working again. Replacing the control head with one from the junk yard solved this problem twice. So when I sent a GMC Jimmy to the parking lot in the sky, I pulled that control head from it along with the wheels and a few other items.
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Wednesday, May 20th, 2020 AT 8:52 PM
Tiny
JOE THE MARINE
  • MEMBER
  • 62 POSTS
  • 2002 CHEVROLET BLAZER
  • 4.3L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 173,040 MILES
When I use my climate control switch and turn it on for the floor only I get heat coming from my vents more then the floor. Also, when I put it on defrost, very little blows to the windshield and I hear the compressor go on, which I know is good. I also replaced all of the vacuum lines under the hood, drivers side and even replaced the vacuum ball to make sure there was no leaks. I also looked under the drivers side to checked and seen that all the vacuum lines are okay and even replaced the whole climate control unit in the front dash. I am lost on this one. Many people say its the actuator by the heater box, which I know is very hard to replace. Could this be the problem?
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Tuesday, December 29th, 2020 AT 8:57 AM (Merged)
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello, I'm Danny.

It sounds like you are having an issue with the mode door actuator. Does your Blazer have the automatic or manual control? Get back to me when you can and I can send you instructions on how to replace. Thanks for using 2CarPros.

Danny-
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Tuesday, December 29th, 2020 AT 8:57 AM (Merged)
Tiny
JOE THE MARINE
  • MEMBER
  • 62 POSTS
Manual, I have to turn the fan speed switch to control the speeds. I hope this helps. Thanks so far.
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Tuesday, December 29th, 2020 AT 8:57 AM (Merged)
Tiny
JOE THE MARINE
  • MEMBER
  • 62 POSTS
Also, I believe you want to know if I have to turn the dial to what I need. I do.
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Tuesday, December 29th, 2020 AT 8:57 AM (Merged)
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again,

Here is a tutorial showing what is involved for the blend/mode actuator:

https://www.2carpros.com/articles/replace-blend-door-motor

This is an electric motor that opens/closes to direct air flow through the proper ducts. I've attached step- by- step pictures below including the location on the HVAC box under the dash board.Hope this helps and thanks again for using 2CarPros.

Danny-
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Tuesday, December 29th, 2020 AT 8:57 AM (Merged)
Tiny
JOE THE MARINE
  • MEMBER
  • 62 POSTS
Danny, thanks for the information. Checked in the glove box area, and mind is in the back, looks like I have to pull the dash to get to it. Also, I see that it is facing up in mine, as I went to the junk yard and there was a dash already pulled out. This looks like it is going to be fun to do. The images you sent were for another vehicle not mind. Any ideas on how to get to the problem?
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Tuesday, December 29th, 2020 AT 8:57 AM (Merged)
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

I attached the picture of the mode actuator prior which sounds like your problem. However, I'm attaching more pictures of your HVAC system so let me know if anything in the pictures are what you are talking about with the junkyard dash and I'll get back to you with more information. Hope this helps and thanks again for using 2CarPros.

Danny-
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Tuesday, December 29th, 2020 AT 8:57 AM (Merged)
Tiny
LAURIAT
  • MEMBER
  • 1 POST
  • 1999 CHEVROLET BLAZER
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 136,000 MILES
This started when I replaced the battery. The A/C worked before new battery installed. Afterwards, the A/C worked however extremely hot air was coming through the vents no matter what temperature setting was. Also really bad smell was coming in as well - smelled like antifreeze. Checked all fuses and they were fine. Coolant levels fine. My mechanic had to clamp off recycling hose to prevent heat from coming through vents. My mechanic checked out motor that controlled the vents and replaced the actuator which got the vents working again, but could still smell odor. My heating coil is not broken - no dripping onto floor boards or spraying of windshield. No leak in the radiator either -- water level and antifreeze are fine. Weird part is that odor comes through whether I have the defrost on, or just using outside air, cold setting or hot setting. Smell is stronger when the Defrost is on and temperature setting is on 78-82. Smell not as strong when temperature setting on 65 and using outside air. My compressor is leaking but by now all of my coolant is gone. Concerned that odor not going away and the more I use the heat the worse it gets.
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Tuesday, December 29th, 2020 AT 8:57 AM (Merged)
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
The heater core sounds like the culprit, have it doublechecked. If you smell it with the blower on in the car it is usually the problem. Both temp settings you tried use outside air, on 65- no heater core airflow, 78-82 w defrost on uses the a/c for the defrost and then you have it on hot by the temp selector which opens the blend door to the heater core. As far as nasty smelling vent in cars, I have had good luck using "Ozium", most parts stores have it. Turn blower on High, temp in the middle with dash and foot nents on and spray it into the grille at the base of the windshield outside the car. Let car air out after you do this
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Tuesday, December 29th, 2020 AT 8:57 AM (Merged)

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