Heater doesn't work at all fan won't blow at any speed.

There could be a few potential causes for this issue. One possibility is that the motor for the fan is worn out or faulty, causing it to cut off at the highest speed. Another possibility is that there is an issue with the electrical connection or the fan control module.
Here are a few steps you can take to troubleshoot and potentially resolve the issue:

1. Check the fuse: Locate the fuse box in your car and check if the fuse related to the fan or HVAC system is blown. Replace it if necessary.
2. Inspect the fan motor: Open the hood and locate the fan motor. Visually inspect it for any signs of damage or wear. If you notice any issues, such as a broken fan blade or worn-out motor, it may need to be replaced.
3. Test the motor: Disconnect the electrical connector from the fan motor. With the car turned on, use a multimeter to test if there is power going to the motor when the fan is set to the highest speed. If there is power, but the fan still cuts off, the motor may need to be replaced.
4. Check the fan control module: The fan control module is responsible for regulating the fan speed. It is typically located near the fan motor. Check for any signs of damage or loose connections. If necessary, replace the control module.

If you are unsure or uncomfortable performing these steps yourself, it is recommended to consult a professional mechanic who can diagnose and fix the issue with your AC/heater fan.

Test the electrical circuits ! Manual HVAC or automatic HVAC ?
Do you know the difference ? Heater / A/C blower motor electrical control diffrent . Manual has resistors an a relay for different speeds , automatic has a blower motor control module .Free wiring diagrams here http://www.bbbind.com/free-tsb Enter vehicle info year , make , model and engine size . Under system click on HVAC ,then under subsystem HVAC controls will pop up . Click the search button , then the blue links . First off you need to know what system yours has , manual or automatic.
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There should be a 30amp HVAC fuse in the fuse box in the passenger compartment. The location should be in your owners manual.
Keep in mind you have an electronic control panel and a control module that manages the blower speed and the other controls. Either one of these components could have failed.

Yes ,Or it could be the blower motor is burnt out,

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read this post on what's causing blower motor to run all the time.

http://ricksfreeautorepairadvice.com/blower-motor-wont-shut-off/
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CHECK THE AC AND HEATER CONTROL FUSE.MORE LIKELY FUSE BLOWED BECAUSE AC COMPRESSOR COULD HAVE FAILED IF LOW SIDE IS OVER 100 PSI. THE REED VALVE PLATE IN COMPRESSOR PROBABLY DAMAGED CAUSED COMPRESSOR FAILURE BLOWED THE HVAC CONTROLS FUSE. HAVE AC SHOP CHECK IT OUT.

You will probably need to replace the resistor behind the dash. Usually the first symptom is the fan will only blow on high but not on the lower speeds. If that is the case, then the resistor ( cheap fix) is the culprit.

If you just lost it all of a sudden, you should check for a bad fuse and will probably find other things that don't work too. Replace the fuse and watch to see that it doesn't go out again - which if it does, you have a short somewhere that needs to be fixed.

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Free wiring diagrams at http://www.bbbind.com/free_tsb.html

Your fan uses resistors to reduce the speed of the fan. Hi speed doesnt use the resistors and that is why it runs on hi. Standing in front of the car, all of your heater housing is on the left side of the firewall You will see a connection with about 4 wires That look like they go nowhere. Take the couple screws out and pull it out. You will be able to see the burnt one.Jump out the burnt on and that will give you another speed or two.