Electric fans and AC.. should fans be at 100% when AC on?

[Scooter]

Getting warmer and now that I have the new fan controller installed and it seems to be running correctly, I'm looking at the AC. The new controller spins the fans up slowly about 6 degrees below a set point to keep my charging system from taking that 60A hit if both fans come on at 100%.

I have aftermarket Vintage Air installed. There is a lead from the trilinear(sp) switch that is supposed to tell the fan controller when the AC is on. It is not currently connected. The new fan controller has accommodation for this function and responds to signal by spinning both fans at 100% as long as the AC is on. Question is what is the downside for not having it connected? If the AC is on it's hot outside and the fans are probably spun up to keep the motor cool. Do I really need both fans at 100% if the AC is on? Stipulate that the inside AC air might not be quite as cool... but is there any risk of damage to the AC system?   

[Dmod1974]

On most cars, one, or low speed is on at all times when the A/C is on to keep the head pressures where they need to be and to allow the system to exchange heat properly. 

The trinary switch closes a set of contacts to kick on both fans, or a high speed when head pressures get too high.  If high side pressure continues to climb, the compressor clutch contacts will open to prevent the system from blowing apart or popping a relief valve.

So A/C on = one or low speed operation at all times

Wire whatever triggers both fans on or a high speed to the trinary switch.

You can also just run the fan(s) at full blast when the A/C is on too.  It'll just draw more current, make more noise, and wear the fans more than really needed.  If you do that, don't bother wiring the trinary switch fan wiring up.  Just wire up the compressor clutch portion.

[Scooter]

^^^ Thanks for the reply. I believe if I connect the lead from the trinary to the fan controller it will run the fans at 100% when the AC is on. No harm really except the draw on the electrical system and noise.

[Dmod1974]

No, it won't kick the fans on until the high side pressures are too high,much higher than ideal cooling pressures and not ideal for the system longevity either.

[Scooter]

No, it won't kick the fans on until the high side pressures are too high,much higher than ideal cooling pressures and not ideal for the system longevity either.

The tech sheet on the trilinear switch says the fan engagement leg hits at 254 psi. Would that be too high?

The switch high pressure cutoff is at 406n psi and low at 30 psi.

Found a video...

[Dmod1974]

You need airflow across the condenser for it to work efficiently. If you wait for the trinary switch to kick them on you're going to be unhappy with the cooling. There's a reason oems run them at low speed or one fan any time the air is on. The trinary switch fan engagement is a backup to bring pressures down at idle or in extreme heat.

[Scooter]

You need airflow across the condenser for it to work efficiently. If you wait for the trinary switch to kick them on you're going to be unhappy with the cooling. There's a reason oems run them at low speed or one fan any time the air is on. The trinary switch fan engagement is a backup to bring pressures down at idle or in extreme heat.

Roger that.

The fan controller lead says "AC signal input(AC on for PWM mode full speed)". The lead from the trilinear switch is a ground. I'm thinking by "signal" they mean 12v. Think it would work if I spliced the signal wire from the fan controller into the single wire that goes to the AC compressor clutch? Fans at full speed when the compressor is on seems like a doable option.

The controller comes with a manual override switch option that bypasses the preset limit and puts the fans at 100%. It's probably intended for fail safe if the controller takes a powder.. but I can probably mount the switch inside the car for when I actually use the AC. Have not used the AC much as I prefer to roll with the windows down even if it's hot. Prefer to not have to do this manually but I guess that would be better than piss poor AC performance when I want to use it.

[Dmod1974]

Not sure what trinary switch you are running, but my Vintage Air piece was 4 wire, which means you can wire it to switch either power or ground.

You can certainly use the compressor clutch power feed to turn the fans on too, but you'll need a diode inline to prevent the compressor clutch from turning on any other time the fans are running (coolant temp switched or manually).

[MoparLeo]

The condenser will only be as efficient as the rest of the cooling system. Ideally the cooling system should be the first consideration as the condenser generally blocks air flow to the radiator making it more important to have a really good functioning cooling system.  You need airflow , Electric fans supply this at low vehicle speeds. As you get to speeds over 45 mph there is more air being forced through the radiator/condenser than the fans can move so they really become unnecessary at speeds. That is why the air cools down at freeway speeds but not very well around town. Airflow...
If your car tends to run hot without the a/c on it will not be able to get rid of the heat very efficiently in your a/c system.
Most people don't realize that the radiator and condenser cores don't cool the car/air down. They just get rid of the heat in the systems. So they must "radiate" the heat through the cooling fins/tube/fins.
Very similar to when you blow air across a spoon of hot food.