the ac fan on my 1997 lexus es300 will not turn to high speed. It just blows slowly. I just replaced the ac control unit in the dash and it seems to run a little faster. What should I do next?

 

It's either the blower motor control module/resistor or the blower motor. Based on the fact the the blower is blowing on low at least, I'd bet the problem is with the blower motor control module/ resistor. If you have a manual control AC, those module/ resistors are inexpensive. If you have an automatic AC (A specific temperature can be set) those are expensive. OEM blowers are expensive.

You can pull the resistor/module out and examine it. You can pull the blower out and attach a 12 volt DC source to it. If it runs at high speed that's an indication the blower motor is OK, but not always. The motor could be failing but a strong DC current could cause it to appear to work correctly. (ask me how I know?)