fan a/c advantages

[kglowacky]

beginning my final chapter of finishing my LS swap. Have read most if not all the threads on fan/relay hook up for ac. I am planning on running the factory ac system. I am NOT looking for diagrams on the hook up as there are plenty of them already posted on this forum. My question is what is the advantages of running three relays so the fans can run at half speed vs running two fans off the pcm and wire with a 3rd relay so
when you turn the ac on both fans come on 100%. I live in Houston and don't see any time I would need them to at 50% in this heat or saying it another way how would it hurt to run the fans at 100% while the ac is on. Thanks Your thoughts

[ls1nova71]

You absolutely want the fans to come on high when the AC is on. The main reason for not running the on high all the time is for noise, and possibly fan life. I have several swaps that only have one fan and it comes on high whenever it comes on and have never had an issue with cooling. I have had to replace the fan motor on one car, but that swap does have over 120k miles on it so I suppose that's to be expected.

[kglowacky]

Thanks I agree. Here is my plan. I already have two fans and two relays working off the PCM. Works great. So I am going to add a 3rd relay independent of the other 2 and find the wire that when the interior a/c is turned on to the trinary switch it will power the new relay and then off the relay I will go to the downstream end of both current relays and hook up there to power the fans

[A1971Blazer]

Looking at the same scenario (whenever body work is completed)

I'm running the Entropy radiator with dual fans....I have had the engine (2002 LS1) running already and it stays really cool with this radiator...so much so that I had to unplug fan 1 to see if fan 2 came on at the set tempº.....

I'm thinking of putting a pusher fan in front of the condenser that would be independent of the radiator fans....it could run when the AC was energized... up until the truck was moving down the road at sufficient speed.

Thoughts?

[lutronjim]

A1971Blazer
How do you propose to cut the fan at highway speeds?
Thanks

[Richard]

Powering the fans or fan relay from the trinary switch is the easiest way. When pressure drops the fans go off. Using the compressor lead is not needed.

[lutronjim]

Richard

This seems like it would run the fan at highway speeds whenever the pressure goes higher than set point even when its not needed. This seems the same to me as triggering fan with clutch power.

Am I missing something?

Thanks

[ls1nova71]

Originally Posted by lutronjim

Richard

This seems like it would run the fan at highway speeds whenever the pressure goes higher than set point even when its not needed. This seems the same to me as triggering fan with clutch power.

Am I missing something?

Thanks

Your fan will never pull as much air as you get going down the highway at 55mph. If your head pressure is high enough at highway speeds to turn the fan/fans on, then you have bigger problems, most likely not enough condenser, over charged system, or something like that. It is not the same as connecting the clutch wire to the fan control which would run the fans the entire time the clutch is engaged.

[Richard]

Originally Posted by lutronjim

Richard

This seems like it would run the fan at highway speeds whenever the pressure goes higher than set point even when its not needed. This seems the same to me as triggering fan with clutch power.

Am I missing something?

Thanks

Think you may be over thinking it. More airflow at highway speeds will lower head pressure simply turning the fans off. Same as not needing an AC switched lead for the fan, if AC is not on pressure will be to low to turn fan on.

Wanted to add I totally agree with what ls1nova71 said. If fans are turning on at highway speeds there is a problem. IMO running the fan/fans at highway speeds can actually impede air flow, so fans off of compressor lead is not recommended by me.

[lutronjim]

Thanks

[Davidf]

Originally Posted by Richard

Think you may be over thinking it. More airflow at highway speeds will lower head pressure simply turning the fans off. Same as not needing an AC switched lead for the fan, if AC is not on pressure will be to low to turn fan on.

Wanted to add I totally agree with what ls1nova71 said. If fans are turning on at highway speeds there is a problem. IMO running the fan/fans at highway speeds can actually impede air flow, so fans off of compressor lead is not recommended by me.

Compressor on, condenser fan on is never a bad idea. Most modern cars work this way in that the condenser fan is always running when the compressor is engaged. If you have cooling problems, you cannot blame it on a condenser fan no matter the traveling speed.