Swamp cooler motor strains, then turns off

Hello everyone. I'm new to this forum and, though I hate to start right off asking for help, I really can't live in my house until this issue is dealt with. Any help is GREATLY appreciated.

We just got this house, and it has an evaporative cooler on the roof that has not been serviced in a while. So I went up there and did all the usual service, went to turn it on and all that it did was hum and then shut off. I climbed up on the roof and had my wife switch it on, and what I saw was that the motor would strain and rotate the pulley slowly about a quarter turn, then shut down.

I removed the belt and tried turning the blower by hand. What I found was that it would turn freely, but not coast if that makes sense. When I say "freely," I don't have a lot of experience to compare to, so I don't know if there was too much resistance or not, but I was able to turn it by hand. From my online research, my understanding is that the blower will not stop the motor unless it is completely frozen, but I'm not sure if that's right.

My next step was to swap the motor out three times - the first and second time for used motors that I believed were good, and the third time for a brand new motor. Call me an optimist. But each of those motors did the same thing. Loosening the belt tension seemed to lessen the strain on the motor and allow it to turn a little more - maybe a half turn - but didn't fix the problem.

So now I'm stumped. Tonight I plan to check the voltage at the motor receptacle (although I'm not entirely sure what to do if it's low). I also plan to increase the ratio on the motor pulley by backing it off a couple of turns. But I'm on the third evening of troubleshooting, and the family is getting restless. Can anybody give me other suggestions to try? I really need to have this thing running ASAP.

Thanks in advance!

 

It would help if you would give us make and model info.

Have you measured the power to the motor?

First suggestion would be to test/replace the motor start/run capacitor, assuming it has one.

Doesn't sound like the fan is seized up, but you try it with the belt off the motor pulley to verify.

 

Thank you for the quick response, Paul. The cooler is a Champion 4401DD. After reviewing the parts diagram, I don't believe there is a capacitor. Assuming that it would be strapped to the motor, I definitely don't see one there. I am open to being corrected, but I just need to be pointed to the right location to find it. Go easy on me - I'm learning.

 

You're right, I don't see a cap in that unit. There is not much to it that can go wrong. You know the motor is good since you've tried 3! Some models have a two speed motor, does yours? If so, have you tried both speeds?

I would measure power at the motor; if that's good, then try it with the belt off. If it runs with the belt off, then make sure the blower bearings have been oiled and back off on the tension setting. The manual recommends setting tension to minimum and then measuring motor amps to set the tension so motor is running at nameplate amps.

Remember that you have to wait for the thermal overload to reset between tests, since it sounds like it is tripping.

 

Thanks for the tips. I will be up on the roof tonight with a multimeter, hoping I only have to replace a control switch! If nothing else, I will be in shape for any ladder-climbing competitions.