I currently have the same issues. Have all the parts, haven’t fixed it yet. Aside from bunk filter being clogged, or blocked. The fan itself may be weak. Looks the same as dash fan, but is different. Different plug, and maybe different rotation. The bunk fan switch is prone to overheating. Eventually needing to replace the short harness, along with the switch. Aside from having bad air cylinders,in the cab, I think there’s 4 of them. The controller itself leaking. I move the selector, just a bit. For now, it stops the leak The recirculating button controls a door near passenger feet. The intake may be plugged. The air intake is on passengers side cowl, outside. Taking out the blower motor, and cleaning the cab intake, and the coils with degreaser, then again with soapy water or any cleaner, no bleach. Rinse it with a garden hose. It should drain out the drain tube. Unless it’s blocked. Or you can disconnect the heat hoses to heater core, leave A/C lines hooked up. And pull both coils out, and clean them. Either way. Same with bunk. Make sure a/c coil and heater core are clean, an air air gun should do it. On the Cab, Taking off the top of center dash, and the side facing passengers, should give access. The dash itself is the problem, You can loosen it up, but doesn’t give much access, I’ve yet to figure out how to remove the controller, without breaking something. Sometimes, you can take the air lines off the quick connects, cut the end off, and reinstall them. Stopping the leak. Good Luck, it’s frustrating, dash breaks easily. Get a picture from the Dealers parts department. Lists all the parts and locations. Helps a lot. There’s a thread on here somewhere, that has much better descriptions The 4 way “T” is sometimes hard to find. 2- 3 way Ts can be used instead.