Thermal motor switch

[Seadog]

Some compressors have a thermal switch mounted in the junction box/capacitor housing mounted on the top of the electric motor. Something similar to this slightly fried one.

View attachment 514912

That senses a current overload, rather than overheating.

 

[carbon]

Not sure why I put thermal switch. Meant overload,

 

[Dragnet]

Lowering the pressure could be problematic, if the switch doesn't have a separate cut-in pressure. Running a tool such that the pressure drops and the motor has to cut in again too quickly is not good. The motors and capacitors have a minimum time they ought to be left before restarting to prevent overheating, which for a 3hp motor might be a couple of minutes. This ought to be on the plates. The inrush current is significant, so I would have thought letting the thing run on the run capacitor for a longer period, with the fan cooling it, is better than setting the pressure too low and the motor having too little time between restarts.

Have you checked the unloader and non-return valve are all working correctly? As mentioned above, a clamp meter will show the peak inrush current.

 

[Vixerfixer123]

Have ordered a new switch so see what happens