Heater circuit heater motor wont wont work only works if a direct voltage applied

The blower motor relay is energized when the Blower Motor Control is set to the High position. This removes the blower motor resistors from the circuit and battery voltage is then applied directly from the HVAC BLO fuse (RH IP Accessory Wiring Junction Block) to the blower motor though the relay switch contacts. The blower motor then runs at high speed.

HVAC Blower Controls Circuit Description
The blower motor is a variable speed motor. The motor operates at a higher rate when voltage is increased to the maximum level.
The blower motor resistors reduce the voltage supplied from the A/C FAN fuse (LH IP Accessory Wiring Junction Block) when the blower control is set at low and medium speeds (speeds 1-4). The blower motor relay is energized when the Blower Motor Control is set to the High position. This removes the blower motor resistors from the circuit and battery voltage is then applied directly from the HVAC BLO fuse (RH IP Accessory Wiring Junction Block) to the blower motor though the relay switch contacts. The blower motor then runs at high speed.

Doesn't have fuse for power windows . Has circuit breaker ,
System circuit breaker (POWER WDWS Circuit Breaker 30A )
Those rarely go bad .
Power Windows System Components
The power window system consists of the following components:
• Window master switch
• Front passenger window switch
• LR window switch
• RR window switch
• Window motors in each of the doors
• System circuit breaker (POWER WDWS Circuit Breaker 30A)
Power Windows System Controls
The power windows system can be controlled by a power window up or down switch activation.
Driver Window Operation
When the ignition switch is in the RUN or ACCY position, or retained accessory power (RAP) is enabled and the window master switch is activated to the DOWN position, battery positive voltage is applied to the window motor causing the window to open. When the window master switch is activated to the UP position, battery positive voltage is applied to the window motor in the opposite direction and the window closes.
The window master switch also controls the front passenger, LR, and RR windows.
Express Down Feature
The driver window will travel to the fully down position when the window master switch is pressed past the first detent. Activating the window master switch to the UP position will cancel the express down feature.
Lockout Switch Feature
The window master switch has a lockout switch which disconnects the battery positive voltage to the LR and RR window switches, disabling them.
Individual Window Operation
When the ignition switch is in the RUN or ACCY position, or RAP is enabled and an individual window switch is activated to the DOWN position, battery positive voltage is applied to the window motor causing that window to open. When the individual window switch is activated to the UP position, battery positive voltage is applied to the window motor in the opposite direction causing that window to close.

The only way to find the problem would be to view wiring diagrams an test the electrical circuits with a volt meter .

Power Windows Operation
The vehicle is equipped with power windows controlled by the door modules. Each passenger door power window can be operated, either from a switch built into the driver door switch assembly (DDSA), or from a switch mounted locally on its associated door. The driver door power window can only be operated from the driver door window switch built into the driver door switch assembly (DDSA).
When the driver door module (DDM) receives a window switch request from the DDSA, the DDM checks the Class 2 serial data to see if the status information is correct (i.e. ignition switch position) to permit window operation to occur. If the status information is correct, the DDM, either supplies power and ground to its associated window motor, or, if the request is for one of the passenger windows, sends a command via the power door serial data circuit to the passenger door module (PDM, LRDM, or RRDM) controlling the window. The passenger door module (PDM, LRDM, or RRDM) controlling the window then supplies power and ground to its associated window motor to move the window as requested.
When one of the local window switches mounted on one of the passenger doors is operated, the associated door module examines the request and checks to see if there are any messages from the DDM prohibiting the movement. If conditions are correct, and no prohibitive messages have been received from the DDM, the associated door module then supplies power and ground to its associated window motor to move the window as requested.

Do you know about computer controlled windows and door lock systems ?

Each door module has its own battery positive voltage supply circuit to use for power window operation, but they are all fed by the same 30 amp power window circuit breaker located in the rear fuse block. Each door module also has a seperate ground circuit to use for power window operation. These circuits are in the same dedicated connector as the window motor control circuits of each door module and are used exclusively for window motor operation.
Each door module also has a battery positive voltage circuit and a ground circuit that are used to power up the module ,as well as, to control mirror and door lock functions. Battery positive voltage to the DDM is supplied through the DRVMDL 10 amp fuse located in the rear fuse block. Battery positive voltage to the PDM is supplied by the PASS MDL 10 amp fuse located in the rear fuse block. Battery positive voltage to both the LRDM and RRDM is supplied by the RRDR MDL fuse located in the rear fuse block. Ground for the DDM is provided through a ground circuit to G200. Ground for the PDM is provided through a ground circuit to G201. Ground for the LRDM is provided through a ground circuit to G302. Ground for the RRDM is provided through a ground circuit to G301.
Window Motors
Each door module supplies battery positive voltage and ground, through the window motor control circuits, to its associated window motor. The window motors are reversible. The direction the window moves depends on which motor control circuit the battery positive voltage is applied to, and which motor control circuit the ground is applied to.To move the window in the Up direction, the module applies battery positive voltage to the window motor Up control circuit, and ground to the window motor Down control circuit. When a window movement in the opposite direction is needed, the module reverses the polarity and supplies power and ground to the opposite circuits to move the window in the reverse direction.

This vehicle doesn't have a blower motor resistor ! It has a blower motor control module , if you have automatic climate control !
If manual climate control , then there is a blower motor resistor assembly !
Blower Motor Control Processor The blower motor control processor controls the speed of the blower motor by increasing or decreasing the voltage drop on the ground side of the blower motor. The HVAC control module provides a low side pulse width modulated signal to the blower motor control processor over the blower motor speed control circuit. As the requested blower speed increases, the HVAC control module increases the amount of time that the speed signal is modulated to ground. As the requested blower speed decreases, the HVAC control module decreases the amount of time that the signal is modulated to ground.
Air Speed - Front Control
The blower motor forces outside air into the vehicle's interior. The vehicle operator determines the blower motor's speed when the driver places the blower switch in one of 5 blower speeds. The blower motor will always operate in any switch position other than OFF, as long as the ignition switch is in the RUN position. The blower motor and mode switches are located within the HVAC control module. The blower motor OFF input is connected in series with the HVAC control module by the off blower motor control circuit.
Depending upon the selected speed, power is provided to the blower motor from either the ignition 3 voltage or battery positive voltage circuits from the fuse block. The battery positive voltage circuit only provides power when the High blower switch position is selected. Power and ground are provided to the HVAC control module by the ignition 3 voltage and the ground circuits.
Low Blower Speed When the Low 1 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the low blower motor control circuit. Voltage is divided between 4 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
Medium Blower Speeds When the Medium 1 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 1 blower motor control circuit. Voltage is divided between 3 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
When the Medium 2 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 2 blower motor control circuit. Voltage is divided between 2 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
When the Medium 3 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 3 blower motor control circuit. Voltage is divided between a series resistor, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
High Blower Speed When the High blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the high blower motor control circuit. The voltage energizes the blower relay, causing the blower motor to be connected directly to the battery positive voltage circuit. The blower motor and blower motor relay are grounded through the ground circuit.
Go on you tube an check out videos on trouble shooting blower motor circuit
Chevy Trailblazer EXT Blower Motor Won Turn Off

Is the coolant level full ? Are the heater hoses hot to the touch ? Do you know where the heater hoses are ? Out in the engine compartment going through the fire wall into the passenger compartment . 2 hoses , one carries hot coolant into the heater core the other is a return back to the cooling system . If hoses are hot you have a temp. door not working . When warmed up what does temp gauge show ?
Temperature Control
The temperature control operates in the following manner:

• Temperature control of the manual A/C-heater system is determined by the position of the temperature control knob (between COOL and WARM).
• This control knob is connected to a potentiometer mounted in the integrated control panel. This potentiometer is electrically connected to the A/C electronic blend door actuator that operates the A/C air temperature control door.
• The A/C electronic blend door actuator contains a reversible electric motor, another potentiometer and a printed circuit board. The wiper of the potentiometer is connected to the actuator output shaft and moves with the output shaft to indicate the position of the A/C air temperature control door.
• Battery voltage is applied to the ends of each potentiometer. The voltage available at each wiper indicates the position of the potentiometer. The printed circuit board drives the actuator in whichever direction is necessary to make the actuator wiper voltage agree with the control wiper voltage.

System uses a reheat method to provide conditioned air to passenger compartment.

• All airflow from the blower motor (18527) passes through the A/C evaporator housing where it can be cooled and dehumidified.
• Temperature is then regulated by reheating a portion of the cooled dry air and blending it with the remaining cool air to the desired temperature.
• Temperature blending is varied by the A/C air temperature control door which regulates the amount of cooled air that flows through and around the heater core (18476), where it is mixed and distributed.

Not sure which window you are referring to but the problem without a doubt is in the switch. If a window motor will move the window in one direction but not the other direction then the fault is in the switch circuit. A window motor is a relatively simple circuit. There are only two wires to it. If you apply positive voltage to one wire and ground path to the other wire the motor moves the window up. If you then reverse polarity or switch the positive voltage and ground path wires then the window moves down. It cannot do one direction without the other also working if the motor is ok. Now just need to determine if the problem is in the main switch or the switch and the door in question.

hi gary ther is a resistor pack that feeds the motor take note of the colours of the wires and the size of the wires that feed the motor and follow them back to the resister block and replace the resister block hope this will be helpfull

Which of these systems does your vehicle have ?
HVAC Systems - Automatic
Blower Motor Control Processor
The blower motor control processor controls the speed of the blower motor by increasing or decreasing the voltage drop on the ground side of the blower motor. The HVAC control module provides a voltage signal to the blower motor control processor over the blower motor speed control circuit. As the requested blower speed increases, the HVAC control module increases the amount of time that the speed signal is modulated to ground. As the requested blower speed decreases, the HVAC control module decreases the amount of time that the signal is modulated to ground.

HVAC Systems - Manual
Air Speed - Front Control
The blower motor forces outside air into the vehicle's interior. The vehicle operator determines the blower motor's speed when the driver places the blower switch in one of 5 blower speeds. The blower motor will always operate in any switch position other than OFF, as long as the ignition switch is in the RUN position. The blower motor and mode switches are located within the HVAC control module. The blower motor OFF input is connected in series with the HVAC control module by the off blower motor control circuit.
Depending upon the selected speed, power is provided to the blower motor from either the ignition 3 voltage or battery positive voltage circuits from the fuse block. The battery positive voltage circuit only provides power when the High blower switch position is selected. Power and ground are provided to the HVAC control module by the ignition 3 voltage and the ground circuits.
Low Blower Speed
When the Low 1 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the low blower motor control circuit. Voltage is divided between 4 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
Medium Blower Speeds
When the Medium 1 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 1 blower motor control circuit. Voltage is divided between 3 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
When the Medium 2 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 2 blower motor control circuit. Voltage is divided between 2 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
When the Medium 3 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 3 blower motor control circuit. Voltage is divided between a series resistor, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
High Blower Speed
When the High blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the high blower motor control circuit. The voltage energizes the blower relay, causing the blower motor to be connected directly to the battery positive voltage circuit. The blower motor and blower motor relay are grounded through the ground circuit.

HVAC Control Module
The HVAC control module is a class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle mode master, provides a device on signal. The control module supports the following features:

If the blower works check for coolant in the cooling system. Test operation of thermostat. Check heater control valve for proper operation if equipped. Pressure test cooling system to ensure system holds pressure (this will help you identify a leak, if any. If car does not over heat and cooling system is in good working order, then the heater core is clogged.
If the blower does not work Check fuse, relay, wiring for short to ground, apply direct battery voltage to blower motor. If blower motor turns on and fuse/relay and wiring are ok replace the switch.

The resistors are in circuit only on the lower fan speed settings.
On the highest speed setting, power is switched directly to the fan motor.
Check fan power supply fuses,
Check power is available to the fan when high speed selected.
If all above OK, apply power directly to the motor to verify fan motor runs- if it doesn't the motor may need replacement/repair.