Cooling fans only turn on when the A/C is on

Tiny
LYNN MOORE
  • MEMBER
  • 2004 BUICK LESABRE
  • 3.8L
  • 6 CYL
  • 2WD
  • 200,000 MILES
Cooling fans do not come on unless AC is on.
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Thursday, March 14th, 2019 AT 5:13 PM

1 Reply

Tiny
SCWICKEDSTANG
  • EXPERT
Hello,

This could be a problem with one of your vehicle's cooling fan relays. A relay is nothing more than an electromagnetic switch that can be broken down into two sides, The control side and the power side. The control side consists of an electromagnet. It has two pins with one wire going to ground and the other wire going to a switched power source, in your vehicle's case the Power-train Control Module (PCM) AKA, "computer". The power side consists of a switch. It also has two pins. One wire is connected to a fused constant battery voltage source, in your vehicle's case fuse 46 and 47 respectively, and the other wire is going to the positive pin on the connector of what is wanting to be powered, in this case the cooling fan. When the PCM commands the fan on it sends electricity to the control side, energizing the electromagnet. The electromagnet then pulls the switch closed allowing battery voltage to the fan, making it run.
Battery voltage is not making it to the fan because one or more of the cooling fan relay could be failing. I have included a couple of links down below for you to go to.

https://www.2carpros.com/articles/how-an-electric-cooling-fan-works
https://www.2carpros.com/articles/fan-clutch-symptoms

Please go through these guides. I have also included specific tests for your vehicle's fan relay. They are straight forward and just require the use of two fused jumper wires. I have also included exploded diagrams and location of the relays, as well as wiring diagrams. Please run the tests and get back to us with what you find out.

Thanks,
Alex
2CarPros
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Saturday, March 16th, 2019 AT 4:15 AM

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