Heater blows cool air - heater is not working?

Tiny
BIGDOGDAD
  • MEMBER
  • 1999 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • MANUAL
  • 112,000 MILES
My S-10 will not blow warm air in the cab. I have had the thermostat changed and it did not seem to solve the problem. The truck is not over heating and the coolant fluid is correct (not loosing fluid). The temp. Guage on the dash says it is about 180 degrees. The strange part is one day it was working fine then the next it day it stopped working.

What else should I be looking for to solve this problem?
Sunday, December 30th, 2007 AT 7:18 PM

48 Replies

Tiny
BLACKOP555
  • MECHANIC
  • 10,371 POSTS
You should firs tfeel the heater core hoses, post back your results, is one hot and the other one cold or significantly cooler? is neither hot, or are both hot? This guide should help us fix it

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

and this video

https://youtu.be/SNRb6pSwYuU

Let me know what you find.
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Sunday, December 30th, 2007 AT 7:29 PM
Tiny
BIGDOGDAD
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They both seem to be warm one might be a little hotter than the other.
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Sunday, December 30th, 2007 AT 7:40 PM
Tiny
BLACKOP555
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In that case you should flush out the heater core and then bleed the system of air. If that dont work post back.
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Sunday, December 30th, 2007 AT 8:35 PM
Tiny
BIGDOGDAD
  • MEMBER
  • 3 POSTS
I flushed the heater core as suggested and it solved my problem. Thank you very much for your support and ideas.

No more blankets required. :D
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Monday, December 31st, 2007 AT 6:40 PM
Tiny
BLACKOP555
  • MECHANIC
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Glad it worked, thanks for the donation!
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Monday, December 31st, 2007 AT 9:02 PM
Tiny
JOHNDVINCENT
  • MEMBER
  • 4 POSTS
  • 1999 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 109,000 MILES
Turn on heat and blower works just no hot air. If it is idleling for a couple of minutes and you turn it on it without driving it you get a very faint sense of heat from the air blowing out but when driving you get nothing but cold air. Should I automatically think heater coil or are there other things to look at first.
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Saturday, October 3rd, 2020 AT 12:17 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Welcome, what does your temp gage show, does it reach normal operating temp? Are the heater hoses about the same temp? Flow through heater return hose?
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Saturday, October 3rd, 2020 AT 12:17 PM (Merged)
Tiny
JOHNDVINCENT
  • MEMBER
  • 4 POSTS
Temp gauge reads about 160. What I thought was a little bit of hot air apparently is none. The hoses going to the heater coil are warm but not hot
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Saturday, October 3rd, 2020 AT 12:17 PM (Merged)
Tiny
TRIGGERDIOBLO
  • MEMBER
  • 3 POSTS
Are you getting vacuum to the heater head (control panel) in the dash, it may not be switching over to heat. If not you will have to track down your vacuum line, it normally is on the passangerside behind the glovebox and is a orange color.
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Saturday, October 3rd, 2020 AT 12:17 PM (Merged)
Tiny
JOHNDVINCENT
  • MEMBER
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Does it matter that when I switch it from cold to hot air you can hear the tone of the blower change but no difference in temp
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
JDL
  • MECHANIC
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If the temp gage is accurate, that isn't normal operating temp, should be higher. You live in a cold climate? The other person has a good idea, also, if those control doors aren't operating like they should.
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
NUMSKULL223
  • MEMBER
  • 1 POST
  • 1998 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • MANUAL
  • 13,000 MILES
Hi, I had a heater hose start leaking today, its the one that come from the driver side, lower Rad hose. I replaced it and poured a little antifreeze in there, and thought I was done. Now the Heater will not blow warm air, and the truck will not heat up over 150. It usally ran alittle under 210. I had heat till today. The heater core isn't leaking. I took the cap off and let it run for an hour, I added more fluid, and it still never heated up. I put the cap back on and drove it around the block and it never got over 150 and the heater never blew hot air. I parked it and I took the rad. Cap off and it didn't spew coolant, it just sat there, Ive never saw this b-4. WHAT DO I NEED TO DO? Help! Thanks
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Try bleeding the cooling system and also check the thermostat.
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
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Subject: Re: no heater
Thanks, I tried that and still nothing, Im wondering if the thermstat is stuck open, Im gonna check it. Where are those bleeder if mine has one? THanks JEff

Check the thermostat
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Recheck the the heater hoses and heater core-could be clogging-backflush the heater core, check the temperature valve-if okay could be a problem with the air mix/blend/mode doors or an actuator/vacuum
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
VORTECTAHOE
  • MEMBER
  • 1 POST
  • 1998 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • MANUAL
  • 124,000 MILES
I have a 98 chevy s10. Its a 2.2 manual transmission. My problem is that it does not run as hot as it should. It seems to run anywhere between 100-160 degrees. I have changed the thermostat, coolant level and for air in the system. I am not loosing coolant also. The truck doesnt over heat and because the T-stat doesnt open I have no heat. Its cold where I live been the weather has never been a problem. Could this be a fan clutch problem, water pump or head gasket? Thanks for your time
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
RHALL77
  • MECHANIC
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Do the hoses feel hot when you are running it. Also if you can I would suggest hooking up a scan tool and see what your temp sensor is readinig. You may just have a bad temp sensor and a plugged heater core. Let me know what you find
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
GARBURCON
  • MEMBER
  • 1 POST
  • 1998 CHEVROLET S-10
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 107,000 MILES
Thought maybe thermostat, replaced that, no change. Just put a new water pump on, checked that and radiator flows fine. Pulled the heater supply line off the water pump and applied the garden hose to it and get no return whatsoever. It happened so abruptly that I have my doughts that the core just pluged up. Is There a electriical component or fuse to the temp control knob on the dash that i'm not finding? Thanks for any help you might give me.
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
Start and warm engine for 10 to 15 min check heater core hoses
both should be hot if not one hot and other warm or cold heater core need to be flushed
if both hot
suspect blend door and or its actuator
under dash in the HVAC box
let me know
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)
Tiny
MOONZUES
  • MEMBER
  • 1 POST
  • 1998 CHEVROLET S-10
  • V8
  • 2WD
  • MANUAL
  • 64,000 MILES
There is no heat comming through the floor vent. All the other vents work but no heat at the floor.
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Saturday, October 3rd, 2020 AT 12:18 PM (Merged)

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