Sealey compressor 3hp 150L (240v - UK) flips thermal breaker often when trying to start.

by Jim
(UK)

3hp 150L Sealey compressor flips breaker often when trying to start.

I have had the above compressor (model SAC1153B - 240v) for about 6 months now after upgrading from my tired little 24L 2hp machine.

I haven't used it too much since I bought it (maybe filled and drained the tank 3 times in 6 months, from new) as I've been busy with other things, but it has now become difficult to start.

Typically when the fault occurs, the motor and pump turn for a few cycles (1-2 seconds max) then the thermal breaker on top of the motor is tripped.

Once the thermal breaker is reset, attempts to start the compressor pretty much continually trip the breaker.

Here are the things I've tried/determined/tested etc:

1) Electrician has checked and confirmed that the power source is fine.
2) Oil level and type is fine (5/w50 synthetic in accordance with the instruction manual)
3) Motor starts very easily if the belt is removed
4) Compressor pump is very easy to turn by hand (ie 1 finger will turn it with ease) when belt is removed.
5) Unloader appears to be working correctly. It hisses when tank is empty up to about 20psi, then stops. When compressor stops it hisses as the pressure is dumped from cylinder/tank feed line.
6) Have replaced the check valve/non return valve, where the air feeds into the tank as I was convinced this was the fault, but this did not really help
7) When the tank is empty, the compressor will normally start just fine
8) Once it succeeds in running, it will tend to restart easily then. If it starts and I allow it to part fill the tank it will typically allow me to stop and start again repeatedly without problems.

The main issue is when it is cold (ie not freezing or even close, but cold in the context of not warmed up from running), and usually with pressure in the tank at the same time.

9) Ambient temperature of my garage where it lives is currently maybe 10C
10) Occasionally, the compressor trips the main fuse that feeds it from the house supply board (16 amp fuse, but not specifically a motor type fuse).

When this happens, it trips the fuse the instant the compressor start switch is deployed, and the motor does not turn at all.

11) Air filter is clean!

The compressor is under warrantee as it is only 6 months old, but I live in a remote area so sending it back would cost me a lot of money that I can't really afford right now.

My fear also is that since the problem is slightly sporadic I might only then get told they can find no fault and have it returned but have to foot the cost of shipping both ways!

My electrician seems quite confident that neither the motor nor its capacitors are at fault. He states that if they were failing, they would exhibit problems whether under load or not, since the capacitors are needed to start the motor regardless of load.


It occurs to me also that the capacitors probably have done their job in a split second, so by the time the motor/pump have rotated several times it would surely eliminate the capacitors from the problem since they're used for that initial spin?

As mentioned the check valve seemed a likely suspect so I replaced it but it hasn't really helped. At first I thought it had, but that was from an empty tank, and the next morning the same problem was back.

The unloader appears to do its job just fine. When the thermal trip is activated, the air does not unload automatically, but the powerswitch is still in the 'on' position of course, and when turned 'off' the air unloads just fine.

This would seem logical and correct to me since the thermal trip is an electrical halt rather than a mechanical one per se and won't in itself activate the unloader.

I have a suspicion it may be the thermal breaker itself at fault, but I have no idea at all how this could be tested/confirmed.

I'd be extremely grateful for suggestions that I can check, as I spent a lot of money on this machine to have one that would last a long time, but due to location it's very difficult to send it back due to ridiculous costs (ferries are involved etc).

Sorry for long post but I figure the more detailed the information the easier to determine what may be at fault!

Thanks in advance.
Jim

_______________________
Bill says...

Jim, excellent post with tons of info. You have done everything you can to diagnose the problem.

That your compressor motor starts and runs with no load is, I think, the key.

Pulling the tube from the pump to the tank effectively removes the load from the motor, since the pump isn't pumping into the tank, but to atmosphere.

You assure me that the unloader is working fine, and if that is the case, then the only other thing that I can think of that you haven't tackled is the valves.

If the unloader is working properly every time, and if you can feel the intake port sucking in air as the compressor cycles, then I wonder about the pressure valve from the cylinder to the tank.

To check that is a tear down job, though and given that your compressor is under warranty, you shouldn't do that as it will void your warranty if you do, I expect.

I'm still betting on a sticking unloader valve. Can you give it a clean before you do anything else?

Cheers and good luck,

Bill