Heater only work on high

I will post and not cover Rear AUX heater box. ok, and is and option

what part of this car has blower
is this HVAC blower failing on HIGH
is this manual version or climate control option.
fuse are blown in cab or in bay (engine)
fuses are first of high speed blower mode fails dead.
what IS A CKED ????? is see no hits in my ASE books on that part or device name in a car or a truck
2003 chevy tahoe , no engine /trans told. (this dictates fuse boxes)
my guess HVAC topic but no sure, what fan/blower or turbo this is.
climate control model has left and right controls and all differenet wiring max. differ.
fuse Hvac1, hvac-ECas, and fuse BOWER< yes 3 fuse must not be blown and the BCM is the brain here.
not scanning the PCM to see BCM errors is a huge error in testing
manual controls the resistor block uses a relay to send 12dc to he blower set to HIGH. all resistors bad ,high still works.

here are the 4 things to fail;
4 is good so 3 things, 2 fuses,
#3 is relay. to fail. a volt meter finds this easy for sure reading this page in the SM.below 3 pins on relay are at 12v.
so are pin F and G 12vdc if not input to them is bad.
not counting bad wires.,

Dual climate control on these is not a manual valve adjuster. It is done electronicly with a electric motor on a valve instead of ran by a maual cable. Find this and check the plug for a 12 volt signal. If you are getting a signal replace the valve, if not it could be a blown fuse, cut wire, or a bad climate contol switch.

you may need to re calibrate the system

Sounds like your controller is bad. http://www.resistorguide.com/applications/blower-resistor/ <Read this info.
http://www.ebay.com/itm/88-94-GMC-CHEVY-TRUCK-CLIMATE-HEATER-CONTROL-93-92-max-SILVERADO-SUBURBAN-SIERRA-/381127684906

I replaced the fan module under the glovebox on my 2005 Town & Country last night. Mine would not shut off at all with key on. It only blew on high no matter where I set the switch. Mine also had the climate control which makes a difference. If it is not the auto climate control it is usually the blower resistor if the other fan speed selections don't blow at all except on high.

I would replace the blower resistor first. its down by the blower motor.

If your only getting high speed, that's a good indicator resistor is going or gone.

Hi, sounds like your blower motor resistor needs to be replaced. If not the resistor, check the blower motor.

Check the relais module located inside under the rh side of the heather box you can see the connector most of them need to be replaced as they burn out you may need to replace the blower motor as well,high amp draw caused by faulty bearings will overload the blower motor controller

yes it will run on high with the resistor unpluged i would have to say your resistor is bad if it does not work at any other speed than high please rate and let me know -jeff