ok so I have a single two speed electric fan right now. its hooked up with a single relay that triggers the low speed when the temp sensor goes off or the a/c turns on.

what i want to know is I have a spare switch in my cab that I want to be able to trigger the high speed and disable the low speed.

so how do i do it?

 

Sticking with standard SPDT Auto relays, this is what I came up with



The high speed SPDT ( 5 pins on relay ) is installed before the currently installed Low speed relay with AC and T-couple.

Any time you turn on the High speed switch, the normally closed contacts ( on the high speed relay ) open, and the low speed relay no longer has power from the battery. The high speed relay now has power on the normally open contacts, and powers the high speed circuit on the fan.

It can be done easier with a DPDT relay, but this could cause a spare parts problem unless you purchase multiples to carry with you ( SPDT are easily found at Napa and the likes ).

 

thanks scully im about to leave for work but im going to do this tonight. every now and then ill blow a relay if im setting still in traffic for a long time. any ideas? its only happened 2 in about 6 months

 

The relay itself is what is blowing ?

If so, maybe try a higher AMP rated relay. There are upto 70 A in a standard Bosch / auto relay package.

The other item to watch on the relay is the cycle rating. Relays have specifications that are in number of cycles, so it could be you are up on the high end of the relay for the cycle count.

One option is to use the Flex-a-lite VSC with your fan, and hook the fan to the high speed circuit.

The FAL VSC will turn the fan on at 60% when the temp limit is reached, and then run it at 100% if the temp raises another 10* F.

There is also the AC hook up and the manual over ride switch input as well.

I got 2 of these for the Troyer fans for dad's 38' RV for redundancy, but dad still has the FAL 270 kit on his F-150. The old style controller lasted ~ 6 years before it took a powder. Just installed the new one this year.

These are solid state controllers, so no mechanical functions in them like the standard Bosch auto relays.

 

Here's another way:



For your desired function, simply move the dash switch between the hi relay & the hi-temp switch.