This is a Renegade 914 with a small block chevy. Aluminum radiator with dual fans up front that automatically engages with a temp sensor. There are two relays on the fan shroud but when the temp sensor kicks, both fans come on.

So, with that information, I also have a A/C unit that is a popular unit sold for hotrods and other custom applications. It mounts pretty nicely under the passenger side and the install was pretty straight forward. What I just learned though.... the A/C unit will never work properly while I'm filling and testing in my garage and I don't reach fan kick on temp of 195 degrees.

My question is this. I need to hook my compressor power wire additionally to my fans so regardless of what temp the car is at, when the A/C is flipped on, the fans turn. on. I'm worried though because what would happen if I had the A/C on with temp below 195 and fans a blazing, then temp rises and hits 195 and gets the signal from the temp sensor to turn on?

Seems like a fairly simple circuit but do you think I would need another relay from the A/C compressor power wire?

I'm struggling with this and bet someone has been down this road and could maybe help me out.

Thanks,

Dave

I'm assuming the temp sender is a switch mounted on the block of the engine and closes its contact to ground when it reaches a certain temperature. This contact likely energizes the coil of a relay which turns the fan on.

Simple connection is to use a second relay where the coil is energized by the AC. The contacts of the AC relay then are connected across the temp sender (ground and sender contact).

AC turns on, fans turn on. Temp > 195, fans turn on. Everyone is happy.

The temp sensor is actually on the radiator but same concept. what type of relay would you suggest? I don't need to worry about voltage if one is already on?

Dave

The standard relay used on the 914 will work fine. Keep in mind that the radiator switch is just that: a switch just like the contacts on the relay. By putting the AC relay contacts across the radiator switch you basically have 2 switches doing the same thing.

I believe what you want to do is have the AC power set a new relay as mentioned above. Agree that the temp switch (sensor) on the radiator likely completes the ground for the existing relays. You would have the AC relay complete the ground for the existing fan relays also, thus wired in parallel with the temp switch.

Does this make sense? Hope I'm not off base with my interpretation of the situation.

The easy way is to buy a dual fan controller with A/C input. All the engineering is done for you.

http://www.summitracing.com/parts/hda-3647
http://static.summitracing.com/global/imag...ns/hda-3647.pdf

Thanks so much once again guys. Sometimes electrical has me scared to death. I sure as heck respect it that's for sure. Here's a pic.... The ground and source are not plugged in yet when this was taken but it's working perfectly. I taped up all the bare surfaces and mounted.

Woooooo Woooooo now onto the A/C which has been a bummer. Had to learn the hard way that because I have no belt fan that's always on when the engine is, well, the damn AC would never cool the high side correctly and the unit was whacked out of it's mind. Only really need to worry about that though testing and filling in my garage OR I guess in severe traffic so it's a good thing that I did this.


DaveClick to view attachment