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Trinary Switch For Fan....Good Choice?

69Sixpackbee on Tue January 08, 2008 1:40 AM User is offline

Year: 1972
Make: Chevrolet
Model: Pickup
Engine Size: 402
Refrigerant Type: 134A
Country of Origin: United States

I am finising up the install of the factory system back into my truck. I previously had the condenser fan coming on and off with the clutch which was not needed when I was moving forward obviously. Since I am going with the POA system and the compressor will be running all the time, would cycling the fan with a trinary switch be the best choice? I figure that the trinary switches are what, around 220PSI for fan switching pressure?
It was either this or a temperature switch of some sort with a t'couple into the condenser fins.

Thanx,
Bud

NickD on Tue January 08, 2008 9:20 AM User is offline

Didn' t this vehicle come with a fixed direct engine driven fan?

If it did, what is wrong with using that?

TRB on Tue January 08, 2008 10:04 AM User is offlineView users profile

With the a/c on I prefer to have an electric fan always on. I just do not see the need to let pressure build up at anytime.

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69Sixpackbee on Tue January 08, 2008 10:44 AM User is offline

Quote
Originally posted by: NickD
Didn' t this vehicle come with a fixed direct engine driven fan?



If it did, what is wrong with using that?
Low speed operation and sitting in traffic at idle causes the vent temps and the pressures to rise, yes? Trying to keep the compressor and system from working so hard. This is what I had on the previous TXV/clutch cycling system and it worked well. Now that I am going with a POA system I was wanting to switch the fan on differently.
Thanx,
Bud

NickD on Tue January 08, 2008 1:00 PM User is offline

One fan I would put in my vehicle is the condenser fan off my 3 ton HVAC outside unit, 1/3HP, 240 VAC and draws 310 watts, but if I put a sheet of plastic around the condenser coil, that drops to about 45 watts, the reason is, the fan isn't moving any air, spinning in a virtual vacuum, and not doing any work. To put that in my vehicle would either need a motor generator or a very long extension cord, motor generators burn lot's of gas. To operate off of 12 volts would need a universal motor that is far less efficient and would draw about 43 amperes that would put a hell of a strain on the alternator that is also very inefficient. Takes at least four times the energy to run an electric fan over a direct fan.

So where are you saving energy with an electric fan when you have the option to use a direct engine driven fan? You are correct, at idle you need all the fan you can get, underhood temperatures rise rapidly and your compressor has to work that much harder, high side pressures skyrocket. Nearest fan I have to my HVAC fan is a directly driven fan in my 454 engine that runs about three times the speed of the engine for quite a blast. Fan clutch is another bad joke along with flex fans, okay guys we have an energy crisis, our engines our only about 14% efficient, and if in good tune that none of them are, we have poor carburetors and piss poor ignition systems, what shall we do? Let's play with the fan, should make the public happy without mentioning the HP it consumes is a tiny fraction of the engines loading. Same with the single drive belt, hey you only got one belt to change now, what they don't tell you if that one belt breaks can get stalled in sub zero weather, helpless and can die.

I even dumped fan clutches back then, even in subzero weather the temperature gauge shot right up to 180*F with that cold blast of air on the engine, and had plenty of heat, and didn't make a dang bit of difference with fuel economy. In the summer, the AC was super cold, even trailering a huge boat, with the clutch, engine would over boil.

So what is the best solution? With FWD, have no choice.

bohica2xo on Tue January 08, 2008 2:25 PM User is offline

So is the electric fan an aux. device with the OEM fan still in place? Or the only cooling device?

If you are looking to switch the fan as a secondary device related to the A/C, I would use a temperature control. I personally like the Cantherm Switch, in a leaded style. The TO220 package is easy to mount, I usually drill & tap a blind hole in the compressor manifold to mount them - but you could simply clamp one (gently) to the compressor discharge line. a 70c switch (158f) is usually a good place to start. Be sure to use a relay, that little switch is only good for 1 amp. Very reliable units in my experience, add a diode across the relay coil if you want the million cycle life.

Even if you are not running the A/C, the fan should run if the compressor body goes over 160f - your underhood is way too high at that point.

B.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

69Sixpackbee on Tue January 08, 2008 7:14 PM User is offline

Hi, guys,

The fan I was using previously on my condenser is a Flex-A-Lite "Black Magic" 12" pusher fan. It is left over from a hotrod project. The engine utilizes a 7-blade thermal clutch fan and a nice tight shroud. I will NEVER run an engine (a large, forward-facing V8 that is) without a beltdriven fan. I was using the condenser fan in conjunction with a relay which is what I commonly do. I realize that the fan is just freewheeling when running along so this is why I really only need it when idling around town and since the POA system is always engaged I was just looking for the most feasable way to utilize the condenser fan with a constantly-engaged compressor.

Looks like the temp switch is the way to go. This is what I was thinking initially when the trinary also came into mind.

Thanx for the help!

Bud

Edited: Tue January 08, 2008 at 7:17 PM by 69Sixpackbee

Chick on Tue January 08, 2008 7:44 PM User is offlineView users profile

Just a note on the pusher fan, location is important, as some can impede air flow.. Should be blowing "near" the outlet of the condenser, never in the middle...Hope this helps..

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Chick
Email: Chick

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NickD on Wed January 09, 2008 6:14 AM User is offline

Come to think of it, my Supra Turbo besides a large engine driven fan also has two six inch factory installed electric fans at the front top of the condenser. Been so long, forgot what turns them on.

bohica2xo on Wed January 09, 2008 12:15 PM User is offline

Bud:

You are in good shape running both fans, sadly many people post here trying to do the job on a big V8 with a single electric fan... and complain about A/C performance.

I forgot to mention that the cantherm switches are available from places like Digikey for a few dollars. They stock them in 5 degree increments, starting at about 65c .


B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Wed January 09, 2008 12:53 PM User is offline

In thermodynamics, even with good computer models, nothing seems to work as predicted, always have to test it. Good to run before and after tests with that additional fan monitoring key temperature points under the hood under driving conditions and can just hot wire the fan for tests.

May find, hey, it's doing some good, not even worth the effort, or it's making things worse. Also may have to play around with the fan placement and that does not exclude the trash can. Won't find out until you try it.

69Sixpackbee on Wed January 09, 2008 7:35 PM User is offline

Quote
Originally posted by: bohica2xo
I forgot to mention that the cantherm switches are available from places like Digikey for a few dollars. They stock them in 5 degree increments, starting at about 65c .
B.


What catalog do you think I referenced even before you told me?? LOL!

Edited: Wed January 09, 2008 at 7:40 PM by 69Sixpackbee

tony1963 on Thu January 17, 2008 9:34 PM User is offline

I like the idea of a pressure switch to run the booster fan. Running down the road, you don't need either the engine fan or the booster fan. However, I wouldn't recommend disabling the engine fan and using a booster fan for all cooling.

For the engine fan, I would always use the factory fan with a thermal clutch. Then, for a booster fan, use a puller fan if you have the space. A pusher fan will, in many cases, simply impede airflow and not do what you want.

My old 85 Suburban pictured below has a factory booster fan (pusher fan) on the front of the condenser but only on the RH side. I have tested it and found that it makes absolutely no impact whatsoever on the AC pressures. It seems to be a waste. It is wired from the factory to a switch on the RH cylinder head and has a relay on the fender. It comes on with engine temperature.

I doubt that it does much for engine heat, either.



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