Turn heater on but blows out cold air instead of hot air.

its probably low antifreeze. or your heating core is going out or your thermostat is sticking and may need to be replaced

HEATER NOT BLOWING COLD,NO HOT AIR FROM HEATER,A/C BLOWS HOT AIR,A/C NOT BLOWING COLD, COLD AIR FROM HEATER,BLEND DOOR ACUTATOR CLOSED,HVAC UNIT NOT OPERATING,
http://alltypesofpartsreplacing.blogspot.com/2012/12/heater-not-blowing-coldno-hot-air-from.html

Your Heater tap is probably stuck in the on posision. This is in the engine bay. Not sure if yors is vacume, electric or cable operated. Temporary fix bypass the heater alltogether ie: put the hoses that go to the tap reroute to the motor

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.

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Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.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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This will help.Thanks.

flush the cooling system, probably clogged. happened to me a bit ago with a 99 cherrokee. hope it helps ya.

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.

plugged heat exchanger is both heater hoses hot valve under hood closed

first feel the heater core hoses see if both are hot if so then your problem is in the blend air door must be stuck on cold. is your blower motor blowing cold air if not your blower motor might be the problem. the blend air door is down by the blower motor.

check thermostat and coolant level

will the air flow switch from floor to the mid to defrost? if so then we have a problem with the tempature door actuator. easy to replace just in tight place. Keep me posted for more help or if this was any help thanks