dual electric fan

Do you mean ac as in air conditioning as opposed to alternating current?

You want to switch on the fans automatically when you turn the air conditioning on?

Are you looking to switch it based on the compressor kicking on only, or on all the time you turn the A/C on?

a/c as in air conditioning. and yes when ever the a?c is on then the fans will be on in slow speed. if it makes the engine get hot then the temp switch will turn them on in high speed. will this do it?

Yeah, I'm not sure what he was planning on picking up for the A/C control input, but since his/her diagram indicates it's a ground switched control, I went with that.

Either the compressor control or the main A/C switch could be used,  Advantages and drawbacks to either method I guess.  If the compressor control is used, the fans will be switching on and off continuously as it cycles the compressor. Normally that'd be harder on the relays with all the extra switching, but since it's the low power mode it might not be so bad. 

Maybe he/she was planniing on using the control switch for the A/C itself, with a ground-when-on output. Either way, that's what I had to assume was being used for the control, since his/her diagram wouldn't have worked if it was high switched.

My suggestion for the A/C would be to have the fans on HIGH whenever there's a call for A/C. Engine heat isn't the reason for fans ON with A/C ON.. it's A/C high side pressure. Some of the newer cars sense this to determine when to turn the fans on during A/C operation. Lack of airflow across the condensor on a hot day with the A/C on will spike pressures and unpleasant $BIGNUM damage may result.

Jim

On June 18 the OP asked..

"ok with this set up how hard would it be to hook ac up to this and have it function the same?"

<shrug> I dunno..

Jim