On Wednesday, the Postal Dude is tasked by Mike J to get A/C parts for his broken Air Conditioner. There are three parts in total.
The first part can be found in the Junkyard without any resistance. The second part is found in the Trainyard Area where it can be purchased/stolen from a vendor. The third part is found in the Asylum where it is being worshiped by John Murray who will turn hostile in the presence of the Postal Dude.