unable to control a/c

Sounds like a bad control module.

 

start with the 12v, that's easy. then move on to the control module as bzap says.

 

the auto mode does change fan speed. for that reason i never use auto mode and keep it in manual mode.

be also advised that a lot of users hit the filtered mode switch and don't understand what it really does.

 

Interestingly the Prius blower motor speed control sends a pulsing signal to the motor to control the speed. Low speed: the pulse is slower frequency. The higher the motor control is set the higher signal frequency. I guess this is designed to save energy from the 12v system. Instead of using resistors to control motor speed they send a pulse. Pretty ingenious, eh? This is why I think there is something amiss in the HVAC module

 

are you really sure? show us the picture of your controls.

 

This is some kinda special filter mode, electrostatic?? We have it too, never pay it much heed.

 

problem solved, happy to help.

 

Problem solved... I hope. The filter mode does, in fact run the fan at high speed for about three minutes. It cycles the cabin air through the charcoal impregnated cabin air filter in volume to clear the cab of micro particulates. If you are flatulent, it does wonders

 

It also works wonders next to dairy farms. We use it often.