proper cooling fan operation?

[kestut]

Can someone state the proper cooling fan operation? I don't think mine are working right. I need help diagnosing what part to replace.
I have a 2014 Tahoe 5.3 Police. I have only had it a couple of weeks. When I first start the motor, neither fan runs. Once the temp gauge gets up around 210 the driver side fan comes on low speed. Passenger fan does not come on at that time. Then once in a while the passenger side fan comes on but only on high speed. Runs a few minutes, then it goes off.
I read someplace that both fans should always run at the same speed, either both low or high. Is this true?
Does this sound like a relay issue?
Thanks in advance

 

[swathdiver]

There are three relays that operate the fans in both modes, seems like one of yours might be kaput.

 

[OR VietVet]

Welcome to the forum from Oregon.

That @swathdiver is such a show off.

 

[kestut]

Thanks! I will check out the relays.

 

[Doubeleive]

or you could have the same issue I have had, pull the fan harness connectors off and have a good look

 

[kestut]

Checked my fan plugs, they both look clean.

So, if I understand the circuit, on high speed they each have their own separate 12 volt circuit (positive and ground), resulting in high speed for both fans. Both fans do run on high speed when it's called for.

If I understand the low speed circuit...the two fans are wired in series and basically sharing the 12 volts so that they each get effectively 6 volts, which makes them run slower. So, if one is running, doesn't that mean that the other must be getting power? So could it make sense that maybe the fan that doesn't run on low speed may be bad in some way? Or am I missing something about the logic of operation? Also, when I spin that fan with my hand, it is a bit squeaky. Maybe it's got bad brushes and only works when it's getting 12 volts.

I think my next step is to test for voltage on the second fan when the first is running on low speed.

 

[Foggy]

They should both be the same: off/ low/ high
both fans together always

 

[kestut]

As an update for future reference. My driver side cooling fan operated as normal. The passenger side cooling fan was only operating at high speed. Low speed would do nothing. I removed the motor and removed the back plate to get a look at the brushes and inside of the motor. The motor had a bunch of 'debris' inside, reddish brown powder stuff. I used contact cleaner to spray that crap out. I put a bit of grease on the shaft end bushing. I put everything back together and it seems to be working OK. Hope it works for a while. I suspect I will need to replace that motor in the future.

 

[Geotrash]

As an update for future reference. My driver side cooling fan operated as normal. The passenger side cooling fan was only operating at high speed. Low speed would do nothing. I removed the motor and removed the back plate to get a look at the brushes and inside of the motor. The motor had a bunch of 'debris' inside, reddish brown powder stuff. I used contact cleaner to spray that crap out. I put a bit of grease on the shaft end bushing. I put everything back together and it seems to be working OK. Hope it works for a while. I suspect I will need to replace that motor in the future.

Yep. Those motors are pretty cheap. Might as well git 'er done before it gives you trouble again.