Relays

[Spanky]

I had a recent issue with my electric cooling fan. I use a manual switch to activate my fan because I had difficulty finding reliable thermostatic ones. Anyhow, I was out cruising and when my temp gage indicated 200 degrees I flipped the switch. Nothing . . . so I cruised on home (temps stayed below 200 a long as I was moving) and determined that it was the relay in the fan circuit. Have any of you had relay failures? I thought they were pretty much failure-proof.

 

[RodStRace]

Fans are one of the toughest things for a relay to control. Any electric motor pulls the most amps at startup when at zero RPM.
The sheer number of OE relays for this shows that they are constantly redesigning them to handle the load for the warranty period and to pinch the cost. Plus the wide range of fan sizes and draws.
The switch VS sensor is the control side and I get the disdain for trusting 'automatic' control. It's the heavy Load side that failed you, though.
You can upgrade the relay to a higher amp rating, just make sure the wiring isn't undersize, too.

OEs have mostly gone to a Pulse Width Modulated (PWM) computer control so this startup high amp draw is mitigated, along with varying fan speed. This isn't going to work for you and your on/off switch. You might research 'soft start' relays, but I haven't checked into those at all so can't offer suggestions.