OT: Air Compressor Update

[Hec In Omaha]

Howdy all,

Last night I removed the tube from the compressor head to the tank. I did this after I ran the compressor and let it trip out at the 125 psi set point. I first loosened the connection at the head and did not hear hissing. So the check valve in the line is holding. Then I removed the check valve to inspect it and it looked good. There were was no gunk inside. I reassembled the compressor and tried to bypass the pressure switch. I basically connected the black wire from the power cord to the black wire to the motor, connected the white wire from the power cord to the white wire to the motor. The green wires were already tied together via a ground bolt on the compressor. When I plugged the plug in it hummed and tried to run but it didn't sound right so I quickly unplugged it before I tripped the breaker. I guess this would rule out the pressure switch? By the way the compressor had 60 psi in the tank when I tried to jump the pressure switch. This is sounding more like the motor or start Capacitor issues? What do you think?


Thanks in advance!

Hec

 

[asphelt]

Sounds to me like the start capacitor.

 

[Ron-MO]

You did not comment on whether or not you have an unloader valve, or if it is working. I still believe it is the unloader valve (not pressure switch). Usually with a bad start cap the motor will not even start with zero pressure. Sounds like it is attempting to start with full head pressure on your compressor.

 

[Hec In Omaha]

Ron,

It does have an unloader valve. It is electrically actuated. I can hear a PSSSSH after the compressor cut outs out. I am assuming its the unloader valve doing its thing? If it wasn't working, wouldn't I have had pressure in the pipe from the head to the tank?

Hec

 

[Beanmedic]

I'll have to agree. While you might first suspect a start capacitor, the clue is that it runs and builds pressure after you bleed it down. A weak start capacitor will SOMETIMES start a motor, but typically won't.

When it pumps up to 125, or while running you turn it off at the pressure regulator using the pressure regulator switch (if it has one), does it give a big HISSSS of air? That is the unloader doing its job. Compressors don't like to start under pressure (very hard to turn). Many of the unloaders are part of the pressure regulator. Sometimes you can trip them manually. Remove the cover of the pressure regulator to get a looksee (power off first). Sometimes dirt daubers like to build in there and foul up the works.

...or remove the belt and see if the motor starts each time you give it power. Then you are diagnosing the motor startup only...

 

[Ron-MO]

Ok, I reread your message and sounds like unloader is indeed working. My next step would be to try a different start capacitor. You may have two capacitors - a start and a run cap. I know mine does.

 

[Beanmedic]

Sorry...I'm running behind with a slow connection.

You heard the unloader...good.

I would agree the start capacitor is next. Would normally suggest putting a meter on the line at the motor to make sure you have proper voltage. Low voltage can act the same way.

You have to get to the capacitor to look at it's uF rating anyway, so check for loose wires on the posts of the capacitor. If you have another motor with a capacitor near the same rating you can temp wire that in to check. Might save you a trip?

 

[36 Coupe]

Its time to buy a new start capacitor.You should have a spare any way.The start cap is the first thing to try.