swamp cooler keeps blowing fuse

I have a swamp cooler problem. it keeps blowing the 15 amp fuse on the low speed. and then ran the high and finaly it blew, new motor new pump, it has a disconnect box on the swamp cooler that has 2 -15 amp buss fuses. They are time delay. amped 0ut the low wire at the switch and it was only pulling 3.8 I was advise to test the disconnect box so I tested each contact inside the disconnect box to see if any volts were putting out or bleeding and it wasn't which wasn't suppose to from my understanding. wires seemed to be tight at the switch, however I went to turn the dial to a lower setting(round dial) so it would kick on and then turned it back up slightly and it blew out. not sure if that indicates a bad switch. another thought could that disconnect box be so old that its contactors are just so bad although I did tried cleaning them with wire brush and electrical cleaner which I thought this was the problem. I was thinking about wiring it directly..question, if I do its running on a 20 amp breaker what happens if it trips that, would my motor be in trouble? any way to test that switch. I do have alumium wire with cooper wires. I did apply anti-oxidant on these connections, I have blown 7 fuses since end of april what can I do now??

 

IF your amps it is drawing is only 3.8, it sounds to me like you have a intermittent short. Inspect all the wires from the switch to the motor and see if you can find any insulation that has worn through and shorting to the steel frame of the cooler.

You could bypass the fuses but you should only protect the cooler with a 15 amp circuit breaker. Do not use a 20 amp! You could burn up the motor.

When the fuse blows, how hot is the motor? It should be warm, but not too hot to touch.

 

Thanks so much ironhand for responding,,,the 3.8 seemed to be ok if the low speed should draw 5. something..shoukd it be crawi8ng close to the 5. someting? I really havnt been able to rush up onto the roof and feel the motor when it blew. my other thought was a possible short like you mentioned.. I was thinking maybe pulling those wires through but not sure if they were stapled or not..but wouldn't they have to split off at a certain point and goto the main panel? providing the short is in the attic somewhere. I did a pretty good inspection of the wires that were visible at the switch and in and around the cooler and all seemed to be fine. I did noticed this morning.. I turned the dial to a lower temp setting to kick it on it first was blowing on high speed then like 2 seconds it switched to the low speed does this maybe indicate or implicate the switch? note, in checkng the panel i do have other circuits on the same breaker would this cause it to overload and then blow it.. but why wouldnt it blow the high as well?
Thanks again for your help and your time

 

I will have to say we do not use swamp coolers in MN due to the fact we have too much humidity already. The only ones I have seen is portable ones. Now that I understand that it is something that is on the roof of the building, that changes a few things.

I doubt you need to inspect all the Romex cable going to the cooler, but just check the wiring at the cooler to make sure there is no damage. You also might want to clean the motor and cooler to make sure you have good air flow.

I suspect it has something to do with the other items on the circuit. Put your clamp on meter on the wire coming off the fuse and turn on the cooler and watch the amps. If it gets close to 15, you have a problem.

Since I have not seen what you are talking about, could you post a picture(s)?