Strange cooling fan issues

[userx2]

Hello,
I have an interesting problem with cooling fans.

These are mains operated 150mm / 6" fans cooling fans of the normal shape.

There are 2 fans next to each other in a unit or our design.
There are a relatively large number of units failing in the field that have started overheating.
The problem is always solved by replacing the topmost fan.

However, testing a number of returned "faulty" fans has not revealed ANY problem with them, They operate as good as a new one, same rpm, airflow, noise pattern etc.
Even when heated to 70dC, no issues.

I am now wondering if there could be an issue where the airflow through the fan goes into a weird "mode" where it no longer flows but rather somehow just spins.

Is something like this possible?
I am not sure what else it could be unless these fans really become intermittent at some stage under some unknown condition.

Best Regards
X

 

[barry]

Wait, what's overheating, your units or the fans? If it's the fans, how do you know they're overheating?

 

[FvM]

There can be a problem if the fans are operated with high back pressure/low flow. The operation range is usually specified as unstable in fan datasheet.

 

[userx2]

Our unit is overheating due too little airflow from the fans. The fans are not overheating.

--- Updated Feb 16, 2023 ---

There can be a problem if the fans are operated with high back pressure/low flow. The operation range is usually specified as unstable in fan datasheet.

That is a very good point.

--- Updated Feb 16, 2023 ---

I can add that our design used a different fan before which was more noisy but wuith very similar specs. We had no failures then except for some noise complaints.
The fan in question is of the quiet blade design and is less noisy for about the same specs.
The blades are shaped differently.

Regards
X