2005 Jetta TDI Issue with ac/ heater blower motor

I have Jetta TDI 2005. My fan is working on first 3 lower speeds , but on the 4th speed works around 30-45 sec then stops. When I turn OFF motor for about 1 min motor works normally on first 3 speeds , but there is still the same issue with the 4th speed.
I've replaced the resistor but the problem is still there. Is there any way to test the motor blower to be sure that that is the problem? Could it maybe be a relay?
Thanks

The only difference between high speed and any of the lower speeds is that highest speed bypasses the resistors. This gives the motor full voltage. Your symptoms suggest that motor is overheating with full voltage. Look at all the terminal connections too for corrosion that might be heating up with the full current draw.

FYI, a bad resistor block usually means the motor won't work at low speeds but works at high speed.

Measure the voltage at the fan while it's running on high, see if it cuts out.
If it does, trace back to fuse 25 inside the car.

I think the dash switch grounds behind the right side kick panel.