Peterbilt evaporator/heater core cleaning...

It's under the glove box and behind the plastic kick plate on the passenger side. Take those out from the inside, then there'll be a metal plate held on with a few screws. Take that off and you'll see the evaporator and heater core.

 

Better suck and not blow. A shop vac won't get the debris all over your cab.

 

I just went through this with my 02 pete.I bought three cans of brake clean and sprayed the crap out of it.Make sure u do it after the truck or ac hasnt been on for a few hours so its dry.You wouldnt believe all the black sludge dust etc... that fell out of it.it dropped the temp out of vents about5-10degrees.we use to use this method when i worked at the garage all the time.and it wont smell up the cab.