pressure switch

It sounds like you should have two lines. One is where the air goes into the back of the pressure switch (where it is mounted on the tank or manifold. Make sure the diaphram in there doesn't leak (kinda unusual). The other little aluminum line you're talking about is the unloader (like LTF said). That little spring, O ring and plunger is essentially a schrader valve (like in a car tire stem). Your pressure switch should have a arm coming out the side which pushes the plunger and lets air out of the compressor head (via that little line). When the pressure switch shuts off the motor, a little arm hits that plunger and you hear a hiss like then you press the plunger in a car tire stem to let some air out. Should last a second or two until the pressure is relieved out of the compressor head. Some let air out of the head AND the compressor to tank air line (in which case you NEED the check valve). If it just continually leaks slowly, it's most likely clogged up somewhere, and it's taking longer than it should to relieve the pressure. If the whole compressor setup is wrong, and the switch works right, it would sound (and act) like continually squeezing the trigger on a smallish blow gun.

First, if the compressor pumps up and shuts off when it's supposed to, it's probably worth working on.

Next, like LTF said, you should probably have a check valve installed where the air from the compressor goes into the tank. I just bought one for $12 from Grainger.

Now, check to see if the pressure switch moves that little arm when it shuts off. It's mechanically connected to the electrical contact assembly. If it does, just clean everything up, replace the O ring and put it back together. Doesn't matter if it leaks a little, you won't lose air out of the tank with the check valve.

Let us know how it goes!

Tools

I had to replumb the aluminum line, as someone else had broken it off. When I took it off the pressure switch (which sits on top of the hose valve), it fell apart, and I'm not sure I got the parts back together in the right order. Plunger first, then spring then o-ring (which seems pretty stiff, like plastic). I don't see any really good way for this thing to seal off at all.

Would I be better off just capping the unloader at the check valve? My older model had all the same lines, but no unloader or pressure switch.

Pretty long winded, but I really appreciate the help, and I want to take another crack at it tonite.

You can buy a new pressure switch/unloader for about $30 so there really not worth messing with. You will need the unloader as without it makes the starting current to high on the motor and will burn the motor windings, if the motor will start without a unloader, most won't.

If the pressure switch/unloader valve is working correct, you don't need a check valve as the combination switch has a built in check valve.

T_Bone

T_Bone