Truck losing air pressure while stopped can’t find leak

[snailexpress]

Before diving for new compressor check compressor unloading valve. Disconnect compressor intake, governor tube and outlet. Spray liberal amount of WD 40 in governor connection and intake.
Cover outlet with big rag, safety glasses on. Start engine and spray WD 40 in intake ntill all carbon is out.
Check pressure with finger like mechanic did.