Air leak or air dryer?

Did you soak everything down with soapy water? It will tell you pretty fast if you do.

 

Check if the heat on the air dryer is working,check for voltage at the plug.
Since its a new to you truck replace the cartridge anyway,

 

Install a "T" fitting into the signal line for the unloader to the air compressor. Apply shop air to this. This will pressurize the entire signal line, unloaders in the compressor and air dryer and the line itself to the air tank. Now you can check for leaks.

 

that is a great idea! thanks

 

If you have the same AD/IS dryer that’s on my ‘05 prepare yourself for a never ending purge valve nightmare. Had both audible and inaudible leaks that in the end turned out to be the purge valve. Both AD/9 and AD/IS dryers will drive you nuts with purge valves. That said, I’ve always had dry reservoirs so they may be worth the headache.

 

Yeah I put a brand new, not reman, AD9 on sometime last year and within a couple of months had to replace the purge valve I guess they don't make them like they used to or maybe they do?