Pump works on high but not on low

[Kathe]

This is our 4th summer with this filter pump. Last fall it quit working on low and only on high. After we closed the pool, we took it to be looked at. They couldn't find anything wrong. It worked for them. They said it must have an overheating problem.

This spring it has worked fine for 3 weeks and now the same problem is occurring again. If it is overheating why would it work on high and not on low?

 

[niteshift38]

This sounds interesting (I know not from your perspective ). Hmmmmmm!!! Will it start on LOW after sitting for awhile (by "awhile", I mean does the casing feel like the air around it temperature)? How far from the power source is the pump (i.e. No extension cords)?

 

[Kathe]

Hi! No extension cords. Close to power source. It has now started up on low again and has been running okay for a few days. It's such a weird thing to not work on low when high will work.

 

[niteshift38]

Hi back! So it started on low and has been running on low for a few days with the problem being when running on high and then switching to low other times?

 

[Kathe]

No. We run it on low continually. Sometimes it stops while running on low. But...we can turn it to high and it will run. It always works on high no matter what. It is the low that sometimes stops and we can't figure out why it does.

 

[tstex]

Nowhere have you mentioned the make and model of the pump? How is the pump being powered and where is the placement of the pump relative to your pool?

It sounds like it can only run for so long under certain pressure levels, then shuts the pump off due to heat, but the higher rpms is not stressing out the pump...

 

[Kathe]

It is a Century Pump. 2 speed. On our 4th summer with it. Was in for a check up last fall. Powered by electricity and sits right next to the pool on the ground next to the filter.

 

[trickle]

Low speed usually has a start winding and or capacitor that drops out once the motor is spinning. Newer motors can have a centrifugal switch that does the same. Mine has a micro switch and a centrifugal disc that causes the start winding to drop out once a certain rpm is achieved, and then the slow speed winding takes over. When my microswitch broke (not available anywhere Hayward!), I made the unit work at low speed by simply starting at high speed and then switching to low speed, which is what the automatic controller allows for and even recommends anyway. The low speed windings generally does not have the power to start by itself, without a start winding switching process being involved.

 

[Kathe]

Ours has a pause between high and low. If it is on high and I want to switch it to low, it actually turns off before I can start low and visa versa.

It shut off on low again today. It had worked on low continually for 2 weeks. Only working on high now. I'll see what it does tomorrow.

 

[niteshift38]

Most times a motor overheats, is because of resistance (be it a pump, bearings, etc.). I've yet to see one only do that on ONLY low speed. Just for a reference, my filter runs at 14 PSI on high speed and 4 or 5 PSI on low speed. Are you around when it shuts off? If so, is the casing too hot to touch, or will it eventually restart itself after cooling down? Without knowing the actually amperage draw at each speed, it is tough to diagnose. I'm leaning to some sort of resistance from the pump itself (the "load") or the motor is undersized for that pump rating (doubtfully the later, because it had been working fine). That would account for it testing fine on a bench (with no load attached), but having issues when attached to pump unit.

It is baffling me that, if it is a thermal in the motor tripping, that it does it so intermittently. Are all vents (if any) clear from any debris? Might b a dumb question, but the motor is not covered or anything that would restrict airflow? Knowing the amp draw would be VERY telling.