Hi guys. Hooking up the fans for the radiator. Went with the kit from DeWitt. Fit great. I will have AC, but for now both fans will tie into the water temp. Do I really need another relay for the AC? Will that mean I will have to remove one of the two relays going in now? Thanks for your experience.

 

YES...I installed another relay and called it "A/C REQUEST' and labeled it. What it does is that this added relay....when wired CORRECTLY....will take the 12 volts that will power your clutch in your air compressor and supply power to the COIL in the relay and when your turn your A/C ON....and this 12 volts is what is providing the 12 volts you need for the coil in the relay....and the relay is wired in and is ACTUALLY supplying a GROUND to your two relays for your new electric fans....WHICH is the EXACT SAME thing as your temp sender will do in order to turn on your electric fans when it gets hot enough. VERY SIMPLY CONCEPT.....and YES...it works perfectly

AS for these fans being used WHEN the A/C is turned on....I would BET that when you have your car over at the A/C shop...(which you WILL WANT TO DO)...and they have the gauges hooked up to you system to see what the pressures are while running. You might be amazed that when you ONLY allow one fan to run when the A/C is on what eh HIGH/LOW side pressures are...and when you have BOTH fans running....how it effects the pressures.

So...for this NEW relay....it will take the 12 volts from the wire that goes to your A/C compressor. NOW you splice into the wire before the pressure switch or after. IF you do it after...and the Freon is low....then the fans will not come on....because the 12 volts will stop due to the pressure switch is OPEN. Goes to terminal 86 in the new relay

Then you will need a GROUND wire that will go to the other side of the relay for the COIL. Goes to terminal 85 in the new relay

Then another GROUND Wire that goes to terminal 30 in the new relay.

And ten....a wire from terminal 87 in the new relay that goes into your fan relays that the terminal is the switched control...which is the ground from either a manual switch or the temp sensor.

DUB

 

Thanks DUB. I must confess 12V elec is like algebra to me. Bottom line, the best approach is to add a 3rd relay, for the AC. I need to find a good shop to complete the Vintage Air install, and hopefully this relay.

 

Dub's explaination is exactly how Spal instructions say how to wire up the AC to trigger the fans. I just don't happen to agree with the need to do so and here is why...

I have had many C3's and most of my cruising was highway. If you are going over 40 mph, you don't need the fans on but you might want the AC on. Wiring it up to be automatic with the AC forces the fans to run, even if you are going 75 mph.

My second reason is that the AC will probably turn on the fans, even if they are not wired to do so. That is because the AC will add additional load to the radiator coolant, the switch will sense this rise in coolant temperature, and the fans will turn on.

Some people will say that by switching the fans on with the AC that you start cooling earlier and that lasts about five minutes and then the temperature settles to where it would have been anyway. It's just like the misguided theory about low thermostats getting started earlier. The temperature will still go to wherever it was headed.

I say keep it simple, wire it with two harnesses and let the AC do whatever it needs to do.

 

Thank you very much for your input. Your reasoning makes sense to me. The other approach did not make mechanical sense to me. PS thanks for a well made product! One of the few after market pieces that actually fit without further modifications on my part!

 

I'd have to agree with Dub on this. You absolutely want the fans on with A/C on. The condenser needs to have air passing through it to cool the freon that is passing through it.
Without air through the condenser it will overheat the condenser the pressure in the system will rise and the high pressure switch will activate shutting down the compressor via the clutch. This will cause a cycling of the A/C system and compressor as it bounces off the high pressure switch cycling on and off.
The pressures, as Dub pointed out, will rise dramatically in the A/C system encouraging more leakage at any weak point such as the seal on the main shaft of the compressor. In addition you will experience rises and falls in the temperature coming out of your ducts and will not get the cooing in the cabin that you want.
The fans will be running at highway speeds. So? If you don't like that then install switch to eliminate that relay electrically and use it at highway speeds, but then you got to remember to flip a switch.

 

Or just add a switch to turn the fans on when you want them, without the cost and mess of a third harness

 

Interesting conversation on this topic. I am setting up a manual override switch to the fans. Thanks again to everyone for the input.

 

Here's how I did it-

I have only one Spal fan coming on w/ the AC - but both w/ temp.

I added a speed switch in the diagram- on mine I have it controlled by my ECU via throttle % and VSS. I would ADD a red light so you don't forget!!!

Can easily add a manual switch to a ground.

I have two relays out near the fans controlling the battery power-hidden in a Voltage Regulator case and the third relay/diodes next to the ECU.

dual fan ac switchl by richardhayes454, on Flickr



DSCN5180 by richardhayes454, on Flickr

DSCN5177 by richardhayes454, on Flickr

 

Looks to be a good compromise. Electrically more complicated but no overly so and more reliable than a cabin switch that can be forgotten. I like to have a cabin override switch on mine in the event that a temp sensor fails or I want the fans on independent of the temps sensor or A/C.

 

I left my radiator fans alone as they are adequate for both the engine and the AC in most situations. However, in traffic you may need a boost and vintage air does have an option for an aux condensor fan. I simply used a spare spal i had laying around an bought a trinary switch and adapter for my receiver dryer. My fan is a little large for the application (overlaps the top and bottom of condensor so some air pressure is lost) but it works fine and since its cycling it tells me its doing whats needed and when its needed. As stated above ... when you are moving the fans really should never kick on as the rushing air should be doing all the work... its sitting in traffic that will get you.

I added an aux fan to the front of the condensor and used a trinary switch on the receiver dryer on the vintage air instead of the normal binary switch.

Then the condensor fan is ONLY on when the condensor temp is high enough to need the additional fan. Sitting idleing or in traffic the condensor fan does cycle so it is being called for.

 

They make temperature probes that attached to the outside of the rad and A/C that tell the fans to turn on. Wouldn't that be the safest and easiest?

 

This is correct, air must move across the condenser for removal of heat so I would wire it to the AC to be sure it is working to full potential otherwise why bother! Have you ever been in a car with a mechanical powered fan and noticed at stop lights the AC sucked, think about it.

 

I have two temp sensors- one for the analog stock GM gauge and a BMW temp sensor for the ECU- which is actually controlling the fans- which I can also pull up on my phone.

Still finishing it up- but a manual over-ride might just be the ticket....w/ a LED light.


As far as AC and electric fans- the expensive German cars still run a mechanical fan AND an electric fan- that comes on w/ the AC and high temp.

I wanted to go that route but the mechanical fan in my application just wouldn't work.

From what I have read the best place to measure temp is near the thermostat.

I still remember the days of sitting in traffic w/ my big block- turning on the heat to cool the motor!!!

Richard

 

I know that if the car is going down the highway that the air is being pulled across the condenser. BUT....when it comes to a stop with the A/C on....that is when the high pressure can go crazy due to not having air being pulled across the radiator.

I did not want to have to install a separate switch on this customers car that would cause for him to turn it on and off all the time. Which is why I wired it VERY CLOSE to what 'Richard454' has shown in his schematic. the ONLY thing I did not employ is a switch that appears to turn OFF the fans when the car is at speed. I honestly thought of making a contact switch at the carburetor linkage.....but seeing how my customer has told me that he can...his own words..."Sell ice cream out of the car'...I feel that the A/C system is working perfectly.

DUB

 

Whew pretty high tech for me. I'm still pretty analog when it comes to this car.

Yep, mine is meat locker in the summer. so cold I have to cycle it off since I usually have the heater core shut off.

 

Great thread with all of the info that I will need to wire mine up w/ my TPI set up in the next few months. Thanks to all.

 

Way years ago we were wiring a buddies weird custom mini truck and he didn't like the idea of the electric fans running with ac while the truck was moving but wanted it on when at a stop, he also didn't want to putz with a switch he had to remember to flick,
He of course had a carb on it what I cam up with was a switch that when the carb linkage was at idle the fans where on when the throttle started to open it opened the switch and killed the fans, a little adjustment and he had it where it worked just as he desired.
in hind site if the ac is on and taxing the cooling system then the fans will come on and need to be on...I'm not sold extra is needed

 

I like that switch mysixtynine posted. That'd be the proper way to control the fans with the AC.

Personally, I'd use the 3-relay 2-speed wiring method. Put 2 temperature switches in separated by a temperature band (for example a 195* and 200* switch) so the low speed comes on first then it jumps to high speed if you still need the extra cooling. Use the switch mysixtynine posted in parallel with the lower temperature switch to bring on the low speed fans.

It's a little extra wiring but the advantages are that the fans are quieter much of the time, you put less wear on the fans and the fans don't put such a large surge load on the electrical system when they come on which means you won't have stuff like the lights flickering at night and the relays will last longer.

 

I sure can!