does anyone know the start up amps of a 91 legacy radiator fan on high speed?

 

in other words starting from a stop with the high speed setting?I need to wire in a switch and a relay to control mine and I don't want to go too low.

Just grab a few fan relays from a junkyard car. I think they use 30 amp slow blow fuses in the fuse panel. Grab some of those too and to can hook them to spade connectors.

If it were me, I would go with the rating for the fuse that controls the rad fan. Should be easily enough found in the fuse box, or listed in the owner's manual on the page showing the fuse lay out.

it's hard to go wrong with relays i once ran a 30 amp fan with a 20 amp relay and it worked fine i never had a problem. relays can take some major abuse

The main and sub-fan relays are on separate circuits with regular 20 amp fuses. So total draw for each fan should be less than 20A.

I don't know if it's called the same thing for DC motors, but you are basically asking what is the locked/blocked rotor or inrush current. The switch really only needs to be sized for the full load current. Switches in that range will usually handle a motor starting load as well. Generally the working limit is 80% of the fuse rating, so the 'continuous' load for a 20 ampere fused circuit would normally not exceed 16 amperes. Relays can usually handle above their rated load for starting loads. The risk is overheating the contacts, which can then cause the contacts to weld together, and then it will not be able to interrupt the load.

Most DMM will also read amps up to a point, usually between 10 and 20 amps for DC... So that might be an option as well. The fan should also list how much power it uses on it somewhere. I believe manufactures are required to list that info on the products they sell. Look on the motor itself and it should say.

 

Oh, and most Bosch style relays are 30amp unless otherwise noted, and you can get bigger. I use a 70 amp relay for my ham radio gear in my car

A standard Bosch relay will work just fine for what you want to do.