I have a small reciprocating compressor for use in a sand blasting machine. Many times it doesn't start properly. If I just switch it on, then it immediately turns off, after a few seconds. I need to keep the switch pressed for a few seconds in order to make it start. Also, after the pressure falls with use, the motor tries to start again but can't, just like when I try to start it the first time.

All the resistances of the motor coils are the same: 3.2 ohms.
Initial current is around 14 A. A few seconds later it decreases to 6 A. I can't tell if it is because of the star-delta starter, because is takes slightly different times each time.

I checked the hose of the the pressure sensor. It had some pressure inside, but after disconnnecting it and letting the air out, the situation didn't improve.

The relay is working. I can guess the timer is working because it shows the light titillating, but have no other circuit to check it.

You can see a video of the problem here: