Turning on the heat or AC doesn't work all the time, no matter what setting high or low. But when it works all settings work fine. Could this be the
blower motor resistor going bad? Don't see any obvious loose wires.

 

Usually when the resistor fails, you won't get the lower speeds, high speed only.

Often this is the ignition switch. Could be the dash switch. Use a meter on the power lead into the dash switch, bump your hand against the steering column and the dash panel. You may find the power comes and goes. Less likely is a cold solder joint in the dash panel.

 

I was having the same problem with mine. I dropped the fan motor and noticed the plug for the wire was not secured very well. Tightened everything up and made sure I had a good connection and no problem since. Try turning the fan on and reaching up where the motor is and jiggle the wire and see if it comes on and off. Just a bad connection for me.

 

When my resistor went bad, I lost the 3rd speed and the 4th was slower. If you remove it and some white powdery stuff falls from it, try cleaning it and reinstall. That should fix it if it's that or just buy another one for around $25.

SJ03

 

What is your model, model year, and type of engine? I can check to see if there are any TSB's that could potentially be related to what you're experiencing.