AC-heat control switch issues

I have a 2003 Impala LS with around 114,000 miles. I noticed today that the control switch that turns on the AC or heat is not fully working right. My switch has 5 levels, and on levels 1 and 2 nothing happens. But when I switch to levels 3-4 or 5 it works just fine.

My question is is fixing this going to involve removing the entire dash from the car? My guess it’s a contact issue, and figure it might be pricy to get repaired.

Are you talking about the ventilation fan speed?

Tester

Yes, that is it.

Typical of a partially burned out blower motor resistor which is located in the blower housing. I can’t say for sure but it is probably pretty easy to get at. At least it is in the GM cars I’ve replaced it in.

Yes, that is it.

How is a problem like this diagnosed to know what is causing the problem