I have a 2012 Chevy sonic. The heater only blows cold air yet no fluid leaking & a/c works fine

You need to fix the coolant leak, then refill and bleed cooling system, then you will get heat and cure overheating problem too

Blend door broken inside heater case assembly need to remove dashboard to remove case to split case apart to replace

the heater vacuum motor and lines needs to be checked.Also get the blend door checked.

NO HEAT ON FLOOR VENTS

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As per your problem mentioned. There are few solved help links to troubleshoot these problems. Go through the list and Click the link below:----

2000 Toyota Avalon: No heat on Passenger Side?

http://whatisbyme.blogspot.in/2012/05/2000-toyota-avalon-no-heat-on-passenger.html

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No heat on Oldsmobile Silhouette?

http://technoanswers.blogspot.in/2012/02/no-heat-on-oldsmobile-silhouette.html

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Heater blows cold?

http://schematicsdiagram.blogspot.in/2012/02/heater-blows-cold.html

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Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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Hot air on the driver's side vents only?

http://repairhelpcenter.blogspot.com/2012/01/hot-air-on-drivers-side-vents-only.html

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Temperature gauge does not move and no heat when heater is ON?

http://technoanswers.blogspot.com/2012/01/temperature-gauge-does-not-move-and-no.html

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1992 Toyota Camry: A/C Control light Flashing and A/C not Blowing Cold?

http://technoanswers.blogspot.in/2012/04/1992-toyota-camry-ac-control-light.html

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No heat, blower blows only cold?

http://technoanswers.blogspot.in/2012/02/no-heatblower-blows-only-cold.html

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Ford F150 Ac only blows through defrost vents?

http://technoanswers.blogspot.com/2012/01/forf-f150-ac-only-blows-through-defrost.html

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Dodge A/C come out of defrost vents only?

http://technoanswers.blogspot.com/2012/01/dodge-ac-come-out-of-defrost-vents-only.html

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Ac vacuum line on dodge cummins?

http://technoanswers.blogspot.com/2012/01/ac-vacuum-line-on-dodge-cummins.html

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Ford ranger AC blows cold through defrost vents instead on cabin vents?

http://technoanswers.blogspot.com/2012/01/ford-ranger-ac-blows-cold-through.html

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2005 Chrysler PT Cruiser: A/C Blows Warm?

http://whoisbyme.blogspot.in/2012/06/2005-chrysler-p8t-cruiser-ac-blows-warm.html

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2009 Mercury Grand Marquis: A/C blows Cold From Defrost Vent Only?

http://whoisbyme.blogspot.in/2012/06/2009-mercury-grand-marquis-ac-blows.html

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AC not blowing through Vents on 2007 Chevy Trailblazer?

http://schematicsdiagram.blogspot.in/2012/04/ac-not-blowing-through-vents-on-2007.html

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Passenger side temperature is warm air out of dash vents?

http://schematicsdiagram.blogspot.in/2012/04/passenger-side-temperature-is-warm-air.html

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These will help.

Thanks.

As per your problem mentioned. There are few solved help links to troubleshoot these problems. Go through the list and Click the link below:----

2000 Toyota Avalon: No heat on Passenger Side?

http://whatisbyme.blogspot.in/2012/05/2000-toyota-avalon-no-heat-on-passenger.html

------------

No heat on Oldsmobile Silhouette?

http://technoanswers.blogspot.in/2012/02/no-heat-on-oldsmobile-silhouette.html

------------

Heater blows cold?

http://schematicsdiagram.blogspot.in/2012/02/heater-blows-cold.html

-----------

Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

----------

Hot air on the driver's side vents only?

http://repairhelpcenter.blogspot.com/2012/01/hot-air-on-drivers-side-vents-only.html

--------------

Temperature gauge does not move and no heat when heater is ON?

http://technoanswers.blogspot.com/2012/01/temperature-gauge-does-not-move-and-no.html

-----------

1992 Toyota Camry: A/C Control light Flashing and A/C not Blowing Cold?

http://technoanswers.blogspot.in/2012/04/1992-toyota-camry-ac-control-light.html

--------------

No heat, blower blows only cold?

http://technoanswers.blogspot.in/2012/02/no-heatblower-blows-only-cold.html
----------

Ford F150 Ac only blows through defrost vents?

http://technoanswers.blogspot.com/2012/01/forf-f150-ac-only-blows-through-defrost.html

----------

Dodge A/C come out of defrost vents only?

http://technoanswers.blogspot.com/2012/01/dodge-ac-come-out-of-defrost-vents-only.html

---------

Ac vacuum line on dodge cummins?

http://technoanswers.blogspot.com/2012/01/ac-vacuum-line-on-dodge-cummins.html

---------

Ford ranger AC blows cold through defrost vents instead on cabin vents?

http://technoanswers.blogspot.com/2012/01/ford-ranger-ac-blows-cold-through.html

----------

2005 Chrysler PT Cruiser: A/C Blows Warm?

http://whoisbyme.blogspot.in/2012/06/2005-chrysler-p8t-cruiser-ac-blows-warm.html

-------------

2009 Mercury Grand Marquis: A/C blows Cold From Defrost Vent Only?

http://whoisbyme.blogspot.in/2012/06/2009-mercury-grand-marquis-ac-blows.html

-----------

AC not blowing through Vents on 2007 Chevy Trailblazer?

http://schematicsdiagram.blogspot.in/2012/04/ac-not-blowing-through-vents-on-2007.html

----------

Passenger side temperature is warm air out of dash vents?

http://schematicsdiagram.blogspot.in/2012/04/passenger-side-temperature-is-warm-air.html

----------

These will help.

Thanks.

As per your problem mentioned.There are few solved help links to troubleshoot these problems.Go through the list and Click the link below:----
Air conditioner blows air but not cold air http://repairhelpcenter.blogspot.in/2012/07/air-conditioner-blows-air-but-not-cold.html

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Car overheats and Air blows hot at idle? http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html

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Heater blows cold? http://schematicsdiagram.blogspot.in/2012/02/heater-blows-cold.html

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Heat blows cold on drivers side and hot on passenger side? http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html---------- Hot air on the driver's side vents only? http://repairhelpcenter.blogspot.com/2012/01/hot-air-on-drivers-side-vents-only.html

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2005 Chrysler PT Cruiser: A/C Blows Warm? http://whoisbyme.blogspot.in/2012/06/2005-chrysler-pt-cruiser-ac-blows-warm.html

-----------
1992 Toyota Camry: A/C Control light Flashing and A/C not Blowing Cold? http://technoanswers.blogspot.in/2012/04/1992-toyota-camry-ac-control-light.html

--------------
No heat, blower blows only cold? http://technoanswers.blogspot.in/2012/02/no-heatblower-blows-only-cold.html

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These will help.
Thanks.

Check out related help links with solutions to troubleshoot the problem:---
Click the link below:---
2004 Toyota Tundra: Oil Gauge and Temp Gauge Not Working?

http://howtobyme.blogspot.in/2012/05/2004-toyota-tundra-oil-gauge-and-temp.html

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Toyota 4Runner: Temperature Gauge Sensor http://technoanswers.blogspot.in/2012/04/toyota-4runner-temperature-gauge-sensor.html

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Temperature gauge sits over half way mark? http://schematicsdiagram.blogspot.in/2012/04/temperature-gauge-sits-over-half-way.html
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Heater blows intermittently and temp gauge goes erratic?

http://technoanswers.blogspot.com/2012/01/heater-blows-intermittently-and-temp.html
------------- No heat on Oldsmobile Silhouette? http://technoanswers.blogspot.in/2012/02/no-heat-on-oldsmobile-silhouette.html
-------------
Temperature gauge does not move and no heat when heater is ON? http://technoanswers.blogspot.com/2012/01/temperature-gauge-does-not-move-and-no.html
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Temperature gauge keeps fluctuating up and down close to red? http://technoanswers.blogspot.com/2012/01/temperature-gauge-keeps-fluctuating-up.html
----------- Temperature gauge on the dash quit working on Pontiac Grand Prix? http://technoanswers.blogspot.com/2012/01/temperature-gauge-on-dash-quit-working.html
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Dodge neon gauges not working? http://technoanswers.blogspot.in/2012/02/dodge-neon-gauges-not-working.html

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Heater blows cold? http://schematicsdiagram.blogspot.in/2012/02/heater-blows-cold.html

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Heat blows cold on drivers side and hot on passenger side? http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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1992 Lexus LS400: Engine overheats, Antifreeze out of reservoir and heater Blows Cold Air? http://whatisbyme.blogspot.in/2012/05/1992-lexus-ls400-engine-overheats.html

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These details will help.
Thanks.

To troubleshoot this types of problem,click the link below :----http://howtobyme.blogspot.in/2012/02/heater-blows-only-from-defrost.html
--------Go through the procedure to confirm the issue.

------
Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html

---------
Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

-----------

No heat on car? http://technoanswers.blogspot.in/2012/02/no-heat-on-oldsmobile-silhouette.html

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Heater blows intermittently and temp gauge goes erratic? http://technoanswers.blogspot.com/2012/01/heater-blows-intermittently-and-temp.html------------Heater blows cold? http://schematicsdiagram.blogspot.in/2012/02/heater-blows-cold.html
---------Car heater blowing warm, but not hot air? http://schematicsdiagram.blogspot.com/2011/12/car-heater-blowing-warm-but-not-hot-air.html-------- Heater/AC blower motor not working?

http://technoanswers.blogspot.in/2012/02/heaterac-blower-motor-not-working-on.html

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A/C, heater, defroster fan, not working? http://technoanswers.blogspot.in/2012/02/ac-heater-defroster-fan-not-working.html Heater problem? http://technoanswers.blogspot.in/2012/02/heater-problem-on-isuzu-trooper.html---------

This will help.Thanks.

To troubleshoot this types of problem,click the link below :----http://howtobyme.blogspot.in/2012/02/heater-blows-only-from-defrost.html
--------Go through the procedure to confirm the issue.------
Engine Overheats and heater blowing cold? http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html
---------Heat blows cold on drivers side and hot on passenger side? http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html
-----------
This will help.Thanks.

Try flushing or blowing high pressure air through the heater core lines. its sludge build up and need to be flushed through heater core only. check antifreeze fluid level. only put in straight antifreeze, do not mix. most people do not know what mixture should be, so be safe and add straight, it will not hurt it, i run 100% straight antifreeze and never had a problem or worry about it ever freezing and cracking my block, heads or radiator cracking.

For this types of problem,i suggest you to check this help links:----Car heater blowing warm, but not hot air?http://schematicsdiagram.blogspot.com/2011/12/car-heater-blowing-warm-but-not-hot-air.html
---------A/C, heater, defroster fan, not working?http://technoanswers.blogspot.in/2012/02/ac-heater-defroster-fan-not-working.html
--------Heater problem?http://technoanswers.blogspot.in/2012/02/heater-problem-on-isuzu-trooper.html
---------Engine Overheats and heater blowing cold?http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html
-----------Heat blows cold on drivers side and hot on passenger side?http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html----------------This will help.Thanks.