Three phase fans used in refrigeration equipment are usually not very hard to troubleshoot.
What's the most common problem?
Single phase power!
If a three phase motor loses one leg of power, it will not run properly. In fact, this is the main cause of motor failures.
Single phasing a three phase motor can damage the motor windings.
This damage can cause windings to overheat.
If the motor has internal protective winding thermostats, they often catch the problem and stop the motor.
If not, the windings can eventually short or go to ground, causing the motor to be replaced.
What causes a single phase condition?
I always look for the following.
1. The power from the power supplier has dropped a leg.
2. The disconnect or breaker has a damaged connection.
3. There is a burnt or damaged wire.
4. A set of contacts on the contactor or starter is not supplying proper voltage.
Also, check for lose wire connections.
Want another common problem?
The motor has the wrong rotation.
Remember, three phase motors can be reversed by changing any two leads.
What do I mean?
If a motor is turning counter clock-wise with wires 1,2, and 3. If you interchange 1 and 3 it will now run clock-wise.
After replacing a motor, always check the rotation.
It's surprising how many times I have found three phase motors running backward.
Here's an interesting story related to this topic.
I once got a call to check a tomato cooler.
When I arrived I quickly noticed the fan motor running backward.
I found this strange because I was the last person to service the equipment.
Oh well, I guessed I had missed one.
But then, I noticed another motor running backward.
Then another and another, in fact they were all running backward!
What had happed?
Unbeknown to me, the packing house experienced a power outage the night before.
The power company had replaced the main transformer.
You guessed it!
They had reversed the leads feeding the refrigeration equipment.
All of the three phase compressors and fans were now running the opposite rotation.
I quickly reversed the main wires and restored the prior rotation.
For a split second, I thought I was losing my mind.
Ain't refrigeration great!
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