Subject: [Shop-talk] More air compressor talk

From: Jimmie Mayfield <[email-masked]>
Date: Sat, 6 Jan 2024 16:21:50 -0500

The recent thread about air compressor oil has reminded me about some 
behavior I'm seeing with my 25gal Craftsman Professional compressor.  As 
I recall, there were two variants of this compressor...mine is the 
horizontal version with separate motor and pump.  Motor is wired for 120V.

For years, I used the guy on a 15A circuit.  Maybe 10 years ago, I 
installed a 120/20A circuit for some woodworking tools and I started 
plugging the compressor into that.

Last fall, I tried to run the compressor on the old 15A circuit with 
about 100psi in the tank and it wouldn't turn over -- tripped the 
breaker.  Removed the belt and the motor started fine.  So I figured the 
start capacitor is probably going bad and the 20A circuit can still push 
enough power through the start windings to get things spinning.  Neither 
of my multimeters can measure capacitance that high so I couldn't test 
test them.

Caps are cheap low-hanging fruit so I replaced both last weekend.  The 
compressor now starts on the 15A circuit but it grunts for a second or 
two before it comes up to speed.  So it's an improvement but definitely 
not the behavior I remember from years ago.

Maybe the unloader valve is also going bad?  It hisses when the 
compressor shuts off but maybe it's not fully relieving the pressure? 
Is there a way to test this?

Any other ideas?

J
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