starting

[greg]

My compressor will start sometimes and and some times not.
When it starts it will run until the tanks are filled. When more air is needed, usually it will try to start but fail.
I'm pretty sure it has something to do with the oil.
The oil spilled from it when I loaned it out and since I refilled it, I have problems with it. Is it worth saving?

[PeterB26]

Since the motor starts sometimes, it isn't seized up from lack of oil.

Very cold outdoor conditions can cause hard starting for any compressor as can operating it on a long extention cord, or a combination of the two. Those are easy to check out. Keep the compressor in a heated house or room overnight to fully warm it up, and plug it directly into the outlet.

If the cold weather is your problem, usually after running the motor for a few minutes the compressor is good-to-go for the rest of the day. So if it has been in your truck or at an unheated job site overnight and it won't go due to being cold, bleed down all the pressure, plug it directly into the outlet and cycle it a couple of tank-fulls to warm it up.

If the cold weather or long extension cords are not your problem, next check the operation of the "Non-return Valve" and the "Compressor Pressure Relief Valve."

The Compressor Pressure Relief Valve is on the back of the pressure switch. It is a small diameter brass cylinder and connects over to the non-return valve by a small diameter tube. It isn't shown on the parts lists either here or in the manual that came with the compressor. Someone said they found a call-out for it at the Hitachi site, but I haven't been able to find that myself. If you take this Compressor Pressure Relief Valve off to check it or clean it, be aware there is a small diameter brass plunger which actuates it that can fall out of the back of the Pressure Switch. Don't loose it and make sure it is properly back in place when you reassemble things.

When the compressor reaches its shut off point, the small plunger inside the Pressure Switch actuates the Compressor Pressure Relief Valve and you should hear a momentary hiss of escaping air. This is releasing the pressure on the compressor side of the Non-return Valve so the motor can restart easily without having to overcome high back-pressure from the storage tank.

If you get that momentary hiss, the Non-return Valve and the Compressor Pressure Relief Valve are working correctly. In that case check your capacitors.

If you don't get that hiss, or if the motor won't start at all, try this test:

First unplug the compressor. Then crack open (crack only, don't remove) the flare nut on the copper tube on the inlet side of the non-return valve to bleed off any pressure. If the compressor has been sitting a while, or if the Compressor Pressure Relief Valve is working correctly, no air will come out; but if the Non-return Valve is sticky, and there is still some air in the storage tank, this might drain the entire tank.

Re-tighten the flare nut after all the pressure is fully released. If the compressor will then start and run your problem is probably with the Non-return Valve and/or the Compressor Pressure Relief valve. Listen for the momentary hiss when it reaches shut off pressure to confirm operation of the Compressor Pressure Relief Valve.

A related problem is one where the Non-return Valve sticks.
In this situation when the compressor reaches shut off pressure the Pressure Switch actuates the Compressor Pressure Relief Valve, but since the Non-Return valve is stuck open the air continues to escape through the Compressor Pressure Relief Valve. This causes bleeding down of the tank pressure until a point just before where the motor is about to be turned on again, at which stage the Pressure Switch's internal actuator shuts the Compressor Pressure Relief Valve.

I hope this helps.

PeterB26