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Heater not working properly?

Tiny
ANONYMOUS
  • MEMBER
  • 2003 GMC SIERRA
  • 196,000 MILES
Truck listed above v6 3.5, heater vent value cabin sticks sometimes open had heat. Sometimes close no heat. Only 196,000 kms.
Thursday, March 7th, 2013 AT 11:48 PM

37 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Try pulling HVAC fuse with key on leave out for 60 seconds and reinstall wait another minute it may reset your actuators if not then check for actuator not getting power. This guide can help us fix it as well:

https://www.2carpros.com/articles/car-heater-not-working

Please run down this guide and report back.
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Friday, March 8th, 2013 AT 3:26 PM
Tiny
THOMHOHN
  • MEMBER
  • 3 POSTS
  • 2003 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
I have a 2003 GMC Sierra 1500 4WD 5.3L
And my AC HEATER only blows from the defrost.
It doesn't work on the front four vents or the floor. I just replaced the control moduel located below the stereo. And it made no difference ' I've also checked all the fuses. What else can I do to repair or troubleshoot this problem?
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
JACOB FED
  • MEMBER
  • 1 POST
Did you check the door actuator that controls where the airflows its prolly a bad mode door actuator
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,128 POSTS
Jacob is correct. Check to make sure it is working whey you switch air flow direction. I believe they are electon your vehicle; however, they may still be vacuum actuated.
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
APTOBILL
  • MEMBER
  • 3 POSTS
  • 2001 GMC SIERRA
  • V8
  • 2WD
  • AUTOMATIC
  • 133,000 MILES
Sitting at idol I have no heat. The faster I drive the more heat I get. In return the slower I go the cooler it gets. The fan works and both lines going into the firewall are hot. I have changed the sensor that goes in the fan under the dash. All the fuses look to be good. I do not smell antifreeze nor are there any wet spots on the floor board. Any ideas.
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,128 POSTS
What you are describing sounds like it is low on coolant. Is the blower motor running?

Let me know.
Joe
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
APTOBILL
  • MEMBER
  • 3 POSTS
Yes the blower motor is running and the collant level was low. But I only added about a cup to bring to cool full line. The warning light would come on every now and then so I added coolant. A short time after that the heater started to act up. Could it now be over full by just enough to do the same as needing coolant?
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,128 POSTS
You didn't overfill it. It will push out what isn't needed. As far as the heater, is the engine running at a normal operating temp? THere is a chance the thermostat is stuck open and the engine isn't warming up enough to create good heat.

Let me know.

Joe
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
APTOBILL
  • MEMBER
  • 3 POSTS
The engine is running at a normal operating temp.
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
MXZERO116
  • MEMBER
  • 1 POST
  • 2001 GMC SIERRA
  • 97,000 MILES
2001 gmc sierra 4x4

Recently had the coolant system flushed, now I notice that the heat is not blowing hot air like it should be. Not sure exactly what the issue could be. Both hoses are warm like they should be, the heater/air door opens and closes like it should when switching from air to heat. I'm thinking it might be the thermostat but not positive?
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
DRCRANKNWRENCH
  • MECHANIC
  • 3,380 POSTS
You could have some air trtapped in the system.
Try the link below as it will guide you to the procedure to release air from a cooling system. If that does not work, the thermostat is most likely stuck open and needs replacement.

Her is the link;

https://www.2carpros.com/articles/vehicle-bubbling-noise
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
M.ZELLER
  • MEMBER
  • 1 POST
  • 2001 GMC SIERRA
  • V8
  • 2WD
  • AUTOMATIC
  • 15,000 MILES
2001 gmc 150000 miles heater does not blow warm air. Blower moter working on all speeds. Engine tempature normal.
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
Check heater hoses by the fire wall if both hot suspect blend door and or its actuator

If hoses not hot or one cool suspect heater core clogged
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Saturday, December 26th, 2020 AT 2:44 PM (Merged)
Tiny
JSTP09
  • MEMBER
  • 1 POST
  • 2000 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
  • 116,000 MILES
Heater problem
2000 GMC Sierra V8 Four Wheel Drive Automatic

I have a 2000 GMC Sierra 1/2 ton. I am not getting any heat in the cab. The engine coolant temp. Gauge reads normal, but I still get no heat in the cab. I have always noticed cold air on the passenger side, but this year there is no heat, is there a vent stuck open
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Saturday, December 26th, 2020 AT 2:45 PM (Merged)
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
Verify that the thermostat is operating properly replace if needed check and verify that heater hoses kinked free and getting hot if not remove hoses and flush heater core if heater hoses hot suspect blend door in the HVAC box


https://www.2carpros.com/forum/automotive_pictures/99387_Graphic1_46.jpg

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Saturday, December 26th, 2020 AT 2:45 PM (Merged)
Tiny
BDELCOLLO
  • MEMBER
  • 1 POST
  • 1999 GMC SIERRA
Heater problem
1999 GMC Sierra V8 Four Wheel Drive Automatic

heater blows hot than cold. Return heater cor line gets cold after blower is turned on. Lower radiator hose is cold too. If you leave blower turned off the return hose from core stays hot. Replaced the thermostat and problum is still there. Also the nipple on the inlet side broke. Can that be replaced?
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Saturday, December 26th, 2020 AT 2:45 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check your water level, it's probably low. Then have your radiator cap checked as this is on e of the big failures on coolant systems. If it's not full your heater won't work right.
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Saturday, December 26th, 2020 AT 2:45 PM (Merged)
Tiny
JAG1216
  • MEMBER
  • 3 POSTS
  • 1999 GMC SIERRA
Heater problem
1999 GMC Sierra Two Wheel Drive Automatic 108k miles

does the 1999 GMC need a thermostat or something else. It's winter and I lost the heat in my truck.
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Saturday, December 26th, 2020 AT 2:45 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Hello, does the engine reach operating temp normally? Does the blower motor work? If you feel of the heater hoses under the hood, are they hot?
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Saturday, December 26th, 2020 AT 2:45 PM (Merged)
Tiny
JAG1216
  • MEMBER
  • 3 POSTS
Yes, and still blows cold air.
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Saturday, December 26th, 2020 AT 2:45 PM (Merged)

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