How do I diagnose AC issue?

AC is not working. Here are the symptoms:

Some minor (but not noticeable) cool air comes out of the vents. Same for heat. Not enough to do anything. Any air movement is super weak.

I am looking to diagnose the issue before I start pulling parts. Blower? Blower motor resistor? Actuator? I need tips on how to diagnose my specific issue. Anything I should look for? Any assistance would be appreciated.

Update:
Forgot…I did replace cabin air filter and it blows cold with a slight knock when it is starting up on max AC

 

I would start with the blower motor. Good chance it could be a mouse nest blocking it up.

 

Pull the plug at the resistor and motor and see of the pins are melted

 

New cabin air filter it and cleaned out. speed picked up and it had a slight knock on starting up. Still weak though. Was dirty with debris.

 

Backprobe the connector at the blower motor and check your voltage with the switch on high, it should be within 1 volt of battery voltage.
If it is but your blower isn't running at high speed your blower motor is failing, if it isn't then you have a poor connection somewhere.

 

What about the air intake under the cowl is it clear?

 

I will give it a look when I get off work.