Bought this little air compressor about 20 years ago from the junk tool store ( Harbor Freight ). I've never had a drop of problems with it, heck it's still using the oil I filled it up with when I bought it. Fired it up a few months ago and it wouldn't hold pressure. Based off of where I'm hearing the hissing coming from I believe the pressure switch has gone bad or maybe something is hung up. The pressure relief valve seems fine. Anybody know of a good way to test the pressure switch ? https://youtube.com/shorts/wIRb7P4MWdA?feature=shared https://youtube.com/shorts/fO0metlzocU?feature=shared
Sounds like the unloader is stuck open. Doubt you'll find parts for HF stuff so it might be time to retire it.
My dad bought the same unit in 2000… my widowed mother still has it. Still runs fine. Sorry no help on suggesting a fix or otherwise.
Our shop has a handy little manifold made of pipe fittings and ball valves for checking pop offs and the like. You gotta have air to use it though. Was mostly used on pressure switches to fine tune 'on/off' settings. If you want to pinpoint the leak, mix a little soapy water into a spray bottle and spray the area down. You'll see it making bubbles. A replacement switch shouldn't be more than $40 or so.
Currently don't have a pressure regulator on the compressor. Ordered this setup from Amazon yesterday. There are tons of these central pneumatic pressure switches on Amazon.
