Heater does not get hot. Fan works but will only blow cold air. Temp control knob is turned to max heat. Engine temp gauge is reading normal operating temp.

hello,
first thing to do is open the radiator cap (when cold) if you have one, other wise look in the recovery bottle and make sure that it is half full of coolant. if full, start the engine and let the engine warm up to normal temp the heater on and on max temp and max fan control. watch the temp gauge and make sure the temp goes to the normal operating area and does not overheat the engine. if temp is ok and you have heat that is hot as normal then everything is ok.if no heat and temp is to high then thermostat maybe bad? if engine temp is ok and no heat then you may have blockage in the heater core and or hoses

Your temp sensor has nothing to do with your heater. The temp sensor needs coolant in order to work properly. So first check the coolant level because if it is low your heater will act the way you describe. Once the coolant gets low enough the heater will blow cold. Another possibility is the radiator cap. After the engine has warmed up it expands when it cools down it contracts. As it is contracting if the cap is weak air can be drawn into the system and cause air pockets to form and will cause the same problem

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

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

------------
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.

there should be a temperature door, but I don't know if there is a cable or if its electric. turn the temp knob, if it feels like it moves anything? I dont have a diagram here at home, but will monday/

If the engine temp gauge reads like normal, then you either have a bad heater core, or the valve that feeds the engine coolant to the heater core is stuck shut. If the temp gauge seems to be on the cold side, or fluctuates from normal to cooler than normal and back, it may be your thermostat is stuck open.

heater valve if you have 1 ,or temp control actuator which is under the dash and takes hours to replace!

jtg

After warmup it still blows cold, or only when cold? Normally the fan will operate independently of engine temp except in some climate controlled vehicles. As long as it blows warm air after engine is at temp that's a good thing. the heater uses hot water from the engine. Obviously the heater can't be warm before the engine is. If it's cold after the engine is hot, there are vacuum controlled "motors" on top of the heater box under the dash that move doors that control heat. Either one of the control motors or one of the doors have stuck or failed. Many also have a control valve on one of the heater hoses under the hood as well. If the engine comes up to temp then the thermostat is good (should be at about 210f) Only remaining item is the core itself which may be internally or externally obstructed.
All this being said, if it's good when the engine is up to temp, leave it alone...it's fine.

I think you could be right about there being air trapped in the system.
Or the heater core(radiator) is plugged.
Either way you need a pressurized radiator coolant pump to put the coolant in without air being trapped.
Although,i have seen it done by jacking the vehicle up high enough that the radiator was now higher than the heater core level, and then the coolant was put in.
But this is dangerous to try.

Replace the temp control on this car, it should be electrical control not cables.