Compressor Hating the Cold

**RustyArc** · 29th July 2015, 08:50 PM

Originally Posted by eskimo

I'd be replacing the start capacitor with one that has lots of mfd's to see if that will get it away in such conditions

I think the start winding and cap is OK, as it gets fast enough to turn the start winding off. It's when it's just the run winding where the combination of cold, viscous oil and high head pressure is too much for it, and the motor slows to the point where the start winding is engaged again.

If it's been a balmy night (2+ degrees) then it starts no matter what the pressure in the tank.

If it's been a cold night (-2 or lower) it'll start with an empty tank, but not with a full one. In that case, if the tank is already pressurised, opening the unloading line gets it started.

**eskimo** · 29th July 2015, 09:27 PM

Yes the centrifugal switch may drop out before the motor is up to full speed. Hence my comment the motor is marginal or a bigger cap may get it to full speed allowing run windings to take the torque and keep going.
Of course starting against a load is what you need to overcome...but what is required...a bigger motor with more grunt?. Or will a bigger cap do the job..I would try bigger cap in first instance as its the cheaper of the two

**RustyArc** · 29th July 2015, 09:40 PM

Originally Posted by eskimo

Yes the centrifugal switch may drop out before the motor is up to full speed. Hence my comment the motor is marginal or a bigger cap may get it to full speed allowing run windings to take the torque and keep going.
Of course starting against a load is what you need to overcome...but what is required...a bigger motor with more grunt?. Or will a bigger cap do the job..I would try bigger cap in first instance as its the cheaper of the two

A bigger start cap may change the phase angle on the start winding, and perhaps the starting torque, but this isn't a problem - the problem is when the motor gets fast enough to drop out the start winding - the run winding alone doesn't have enough torque to hold or increase the RPM. Perhaps futzing with the centrifugal switch so that it stays in longer might help?

Yes, a gruntier motor would probably solve it, but that's pretty expensive, and over-capitalisation for a cheap compressor.

At this point, a manual valve plumbed into the unload line seems like the cheapest option.

**bob ward** · 29th July 2015, 10:28 PM

Low voltage could be part of the problem. The colder the morning the more people there are turning on electric heaters.

**RustyArc** · 29th July 2015, 11:35 PM

Originally Posted by bob ward

Low voltage could be part of the problem. The colder the morning the more people there are turning on electric heaters.

One cold morning when I really needed to have the damn thing going I dragged it over to my newer shed with ample 3ph power. Trying on each phase failed to get it running. This wasn't first thing mind you, probably would have been 10am or thereabouts.

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