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Heater blows cool air - heater is not working?

Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Hi, the control knob, directs vaccum to different actuators. Could be something wrong with vacuum or actuator. I'd have to look at it.
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
CHADD
  • MEMBER
  • 1 POST
  • 1996 CHEVROLET S-10
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 100,000 MILES
1996 chevy s-10 blazer, I just replaced the thermostat and still no heat in the cab. Where is the air bleeder valve for the heating/cooling system?
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
It's probably not that. See if your heater control is getting vacuum and then check your vacuum operated doors to see if they are working or not. That is probably your cause.
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
TONYOSIS
  • MEMBER
  • 1 POST
  • 1996 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • MANUAL
  • 12,000 MILES
Coming to work this morning, I noticed that the heater was not producing ANY heat. What might the possible (most likely) causes be and how would I check for them? Thank you in advance for taking the time to help me.
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
SERVICE WRITER
  • MECHANIC
  • 9,123 POSTS
So it blows at you, it's just cold?

First thing I would check is for low coolant level. The heater core is the first thing that loses fluid, thus heat when there is a leak. If it is low, then fill it, run it, checking for heat and leaks.
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
PJMM
  • MEMBER
  • 4 POSTS
  • 1996 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
Heater does not work on 96 chevy s10. Truck has 95 blazer engine 4.3. Water circulates through motor but does not reach heater core. Also overloads fuel
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Does the engine reach normal operating temp? Take the heater core supply line loose from engine/water pump, bump the starter, any coolant pump out? Don't start it. Maybe the heater core needs to be flushed?
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
PJMM
  • MEMBER
  • 4 POSTS
THis has all been done and there is water getting to and from the heater core. Also has a brand water pump so it cant be that.
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
In your first post, you said water does not reach heater core.

Are the heater hoses hot? Does the blower motor work? Next, I'd have to get under the dash to see if temp control actuator is working.
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
PJMM
  • MEMBER
  • 4 POSTS
We got heat. The wires connecting the heater control were not hooked up. Moving the buttons for some reason did not show this but that is what the problem was. Now we just need to figure out what is causing the fuel overload. Thanks for the reply JDL, appreciate it.
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Use a gage and check fuel pressure. Not only check pressure, check that the pressure holds and doesn't drop like a rock, with everything off. Do you have the spider fuel system?
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
PJMM
  • MEMBER
  • 4 POSTS
I will need to get a gage before I can check the pressure and yes I do have the spider fuel system.
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Some of the national brand autostores used to loan out a fuel pressure gage. 60--66psi.
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
EWHIT
  • MEMBER
  • 10 POSTS
  • 1996 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 149,000 MILES
The heater in my truck will barely warm up. After about 10 minutes it'll feel warm to the touch but will not get hot at all. My temp gauge says about 155 and that's usually as warm as it gets. There's plenty of antifreeze so I don't know what it is. Also air only blows out the top defrost vents no matter what setting it's on.
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
I'd check the thermostat. The temp you listed isn't operating temp. Some systems, if the actuators are vacuum controlled and vacuum is lost, it will default to defrost.
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
EWHIT
  • MEMBER
  • 10 POSTS
I already replaced the thermostat and the switch on the dash because it wasn't actually turning all the way to warm but that only helped a little.
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
The temp you listed isn't normal operating temp. Do you live in extremely cold region? If the heater hoses are hot, maybe an issue with heater core or something under the dash.
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Saturday, October 3rd, 2020 AT 12:19 PM (Merged)
Tiny
RDAMELIO
  • MEMBER
  • 1 POST
  • CHEVROLET S-10
On my 1998 Chevy S10 during the summer the a/c stoped blowing cold air, after about a month of slowly getting warmer. The fan portion was still working. Since I live in the mtns. Of N.C. I don't have to use the a/c very often, so I put off fixing the problem. About a month later we had a cool rain and I turned the defrost on the heated air setting to clear the windsheild and there seemed to be no hot air. I then moved the setting to the floor heat and there was no heat there. Now there is no heat or a/c. The fan blower still works fine for the floor, vents, and defrost. I have had no work done to the truck other than a tune up last summer.
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Saturday, October 3rd, 2020 AT 12:23 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Could be a vacuum problem, an actuator or blend door. see below


https://www.2carpros.com/forum/automotive_pictures/12900_heater_1.jpg

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Saturday, October 3rd, 2020 AT 12:23 PM (Merged)
Tiny
CARKAT
  • MEMBER
  • 1 POST
  • 1999 CHEVROLET S-10
  • 77,542 MILES
I was driving, pulled over to get a text message and all heat from vents turned cold, engine temp raised above normal, all corrected when I drove again. This symptom happen about 2 weeks ago, at that time, I replaced the thermostat, and the symptom went away, also the truck has a random miss, according to Autozone plug in thing, the miss is bad from 0 to 25 mph then only slightly noticed at higher speeds. Also I just replaced the oil cooling lines recently. '99 s10 w/ 4.3 Vortec V6, 4x4 ext cab
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Friday, November 27th, 2020 AT 9:33 AM (Merged)

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