Tried searching the threads, because I know I saw a post somewhere about this a while back, but can't find the diagram I was looking for. I have an electric fan set up that turns on at 180 and want to ad a relay that turns the fans on whenever the ac is on. Can someone direct me to a diagram or easy to follow instructions that will explain how to do it?

 

Hi "J"

It doesn't look like you are getting many takers on this one. Maybe I can get the ball rolling here.

Not to be contrdictory, but I'd like to offer some food for thought on what it is you are trying to do.

Most imports (and some domestic products) that run electric fans have a function to support Air Conditioning. But, usually, it involves either turning a single fan at a higher speed, or engaging a second fan.

Backtracking a little: if you want your single/single speed fan to run all the time the air conditioning is engaged, it's not really going to do much for you. That's because if the truck is operating below the thermostat opening temp, the coolant will just sit in the engine and warm up until the thermostate opens. Then at the given temp at the radiator head (or wherever you have your fan temp sensor) the fan turns on to start cooling.

If you change this so the fan runs all the time when the "Air" is turned on, the engine thermostat will still be closed until the coolant warms up then will start to circulate. So no matter how much you try to precool the coolant in the radiator, the engine is going to heat up the coolant in there AND RESTRICT PASSAGE UNLESS IT IS MAINTAINED AT OPERATING TEMP anyway - unless you remove the thermostat.

So, if you wire so the fan is on all the time with the A/C, all you are doing is eating up amperage for no reason until the thermostat opens. And, after it opens with the fan turned on all the time, it will be the same as before - coolant is above the fan on/off temp where it would turn itself on then anyway.

Now, if you had a two speed fan or a second fan that turned on when the air was turned on it would help you draw MORE AIR in a given period of time and help you cool IF the radiator couldn't adequately cool with the air on and the single speed fan turning.

Long story short: what you want to do won't help you cool, it's just going to wear out your fan earlier and put a strain on your alternator/drive train that is not necessary (amplified by the fact that it is now also turning the A/C compressor.

Ok but enough on philosophy.

If you want to do this anyway, it should be a function of the relay that was included with the unit. If you still have the installation instructions, or can ge them online, it should tell you IF you can wire it for two function switching (both temp and A/C on) (in other words did you buy a fan that was built specifically to support the truck A/C). The fan relay may not support that. If it doesn't, you'll have to get a relay that supports two function switching and install it according to the instructions.

I would venture t say that one post will still intake from the temp sensor, and there will be an additional one that hooks to your A/C power.

I guess if you wanted to, you could always rig a switch to bypas the relay and turn on the fan manually when you want, but I wouldn't do that - if you aren't on it all the time, it could cause an over heat. Or you could pull the thermostat out and set the fan temp lower to cool all the time (if it is adjustable). But then you run the risk of running too cool or cold in the winter.

If it were mine, I'd leave the wiring alone and if possible, run a 140degree thermostat and adjust the temp on the fan for a lower turn on (140dgf) in the summer, and about 160 dgf in the winter.

Sorry I couldn't be more helpful,

Julie!

 

Here is your wiring diagram.
Hope it helps.