Added a pusher fan to my pickup, need recommendations on controlling it.

[StarquestMan]

I got a condenser fan off of a 93' 4runner to help with AC/engine cooling at idle/low speed. I already got the thing mounted up the way I wanted it by modifying the hood latch support bracket and moving the fans mounting points around where I needed them. now I'm to the point where I need to decide on how I'm going to turn the thing on and off but I keep going in circles about how I want to do it. The ideas I have been kicking around have ranged from simply tying a relay into the compressor clutch to using a PWM fan controller module off of a newer vehicle so I can be able to ramp up the fan speed and vary it depending on condenser temp etc. here are the options I have considered:

Tapping power off of the compressor clutch wire for a relay.
paralleling a relay coil across the idle up vacuum solenoid.
using a snap disc type switch on the condenser inlet or outlet to switch on the fan relay (possibly using one on the radiator too).
adding an additional pressure switch to the high side to turn on the fan.
switching the stock binary switch to a trinary type switch.
using a fan PWM fan controller and a thermistor or two for temperature sensing

Some of the things I have been considering are:

Not constantly having the fan turning on and off over and over to save the fan motor brushes, relay, etc.
I learned after the fact that this fan was originally used with a dropping resistor and bypass relay so it would run in a two-speed configuration (so maybe starting it on full blast isn't good for it?).
I also might need to work in some sort of delay so that the fan doesn't turn on at the same time as the compressor clutch to help spread the load out, I think the alternators in these trucks were rated at 75 amps or something? so having two large loads switching on at the same time might not be a good idea.
I like to try and use automotive grade parts when possible and the only way I have seen to go with a thermistor and have a PWM fan controller is to use an Arduino micro controller between the two to convert the thermistors variable resistance to a duty cycle pulse the fan controller can use. So, I would have to mount and make all that stuff waterproof.

[85Ram50]

I upgraded my alternator from the 45 amp to a 90 amp. I got one for a 94 Dakota, changed the pulley by putting the OE one on it and had to use some soft copper pipe to make an insert on the new alt to accommodate the thin swivel bolt. According to the instructions I found on MR50 it all lined up fine. Otherwise your electrical knowledge is well beyond mine. I just got a temperature switch kit off the interweb. I think there is a 120 amp alt for the first gen Dakota's as well.

[StarquestMan]

Interesting that a Dakota alternator can be made to work with these trucks, I didn't know that! I'll have to remember that. I did just replace mine a few months ago. I forgot to mention that all of my sensor ports on my engine are in use, even the one on the thermostat housing has the high temp cutoff switch that kills the AC if the engine temp gets too high. It seems like all the kits I find need a port on the radiator or engine.

[85Ram50]

The fan I just put in I bought for my Dakota. I kept it to put it in the D50. Anyway on the Dakota I used the new fitting they have that you put in the top radiator hose. Search radiator hose adapter. I got mine in a kit with the wiring, connectors, relay and instructions. $35 On the D50 I just got the kit w/o the hose adapter because I used the thermostat housing for the temp switch. I spent the money for the thermostat housing because there is barely enough straight in the moulded hose on mine for the adapter.

here is that alternator upgrade page http://www.mightyram50.net/vbulletin...rnator+upgrade