cooling fan relay issues

i have been having an issue with the relay im using to control my cooling fan on my 06 MINI. originally the car would have two fan speeds, low and high on only one fan. the low speed comes on whenever the A/C is on.it uses a relay triggered by the A/C compressor, them through a resistor and the fan. that system is still intact and working. the high speed fan would be triggered when the water temp reached 225, this would bypass the resistor and give full power to the fan

after having some prior cooling system issues i decided to make it so i can control the high speed fan when i wanted to via a switch on my switch panel. so the leads for the original circuit have been removed , and in place is my relay and wiring harness.

this is the relay im using, 40A SPST 12VDC automotive relay, https://comingsoon.radioshack.com/12vdc-40a-spst-automotive-relay/2750001.html
and these are the ratings for it

Switch voltage: 14VDC
Relay coil rating: 12VDC
Relay coil power (W, mW): 1.6W
Nominal current at 68°: 133mA, nominal voltage: 12VDC
there is also a 40a fuse between the power source and the relay.

twice now i have had that same relay fail. the first time was after driving in traffic and getting out of the car, the fan stayed on. i hadnt used the switch during the drive but the low speed fan would have been on because of the A/C i tried disconnecting the switch, removing the low speed relay and it did not change anything, however when I pulled the fuse from the high speed the fan stopped. from this i determinedthe relay was the issue, assuming it was the heat that may have damaged the relay, i simply bought the same one, and put it under the fan shroud to try and shield it from some heat.

then again today it happened again, hadnt been using my circuit, but the A/C and low speed were on. i pulled the fuse and it stopped.

my real question is, could the two circuits somehow be interfering with one another, causing the relay to fail? do i need to add a diode to stop current from the low speed going back through my relay? they share a common ground, is that an issue? or is it likely that i just need a tougher relay?

sorry for the long post, but i do appreciate everyones help!

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06 MINI Cooper S stage-3

User a 60 amp relay fused appropriately, most cooling fans use 50 amps +.


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