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Discussion Starter · #1 ·
I was hoping someone could point me in the right direction to learn more about this subject. I have a '71 Pontiac station wagon (original 455 slightly bored when rebuilt) that I will be retaining the mechanical cooling fan. It overheats when the A/C is on when idling, so I want to add an electric pusher fan in front of the condenser (This system has a POA valve and does not "cycle" as many systems do). I don't want to wire this fan to just come on whenever the compressor is on. I want this fan to only run when the A/C pressures get too high, so it will kick on when pressure go high when idling but will kick off if I'm on the road and getting plenty of airflow (also, in the winter when I'm running defrost I don't want to pusher fan coming on).

I have heard that a trinary switch may be a good way to do this, but I need to learn more about how this works, where to place it, or what better options may be available to do what I want. For example, maybe a binary switch would be all I need since I will still have the regular mechanical cooling fan and all I need is an simple on and off for the pusher when the pressures are too high (no high and low speeds needed).

Thanks,
Brandon
 

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Well, a simpler way to do this may be to wire the relay to the brakelight switch.

At roadspeed you dont need a fan, but at a stoplight you do. Hmm....
 

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I was hoping someone could point me in the right direction to learn more about this subject. I have a '71 Pontiac station wagon (original 455 slightly bored when rebuilt) that I will be retaining the mechanical cooling fan. It overheats when the A/C is on when idling, so I want to add an electric pusher fan in front of the condenser (This system has a POA valve and does not "cycle" as many systems do). I don't want to wire this fan to just come on whenever the compressor is on. I want this fan to only run when the A/C pressures get too high, so it will kick on when pressure go high when idling but will kick off if I'm on the road and getting plenty of airflow (also, in the winter when I'm running defrost I don't want to pusher fan coming on).

I have heard that a trinary switch may be a good way to do this, but I need to learn more about how this works, where to place it, or what better options may be available to do what I want. For example, maybe a binary switch would be all I need since I will still have the regular mechanical cooling fan and all I need is an simple on and off for the pusher when the pressures are too high (no high and low speeds needed).

Thanks,
Brandon
Hello Vetteman61,

As an abstract point of view, why not investigate the reason it's overheating rather than try to work around it. The car shouldn't have any problems overheating with the air con on, even on the hottest of days. I have a '73 full size Chevrolet with a factory 454 and air con and even in the Southwest 100+ degree days in stop and go traffic the engine never overheats. Obviously the things to check are does it have the proper fan, the proper thermostatic fan clutch and is it fully engaging when hot, do you have the correct and complete fan shroud and lastly and importantly do you have the correct radiator and how is the core on it (are there heavy deposits on the inside or are there fins missing or bent on the outside).

In hot weather you should really hear the fan clutch engage that fan. It will be very noticeable, kind of like an industrial sized leaf blower.

My cooling system is all factory parts, even the radiator, just a brass/copper 4 row radiator. You should have something similar.

Just thoughts.

Cheers
 

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Discussion Starter · #4 ·
Desert,

I appreciate the response. I finished this car in 2015 and my wife wrecked it shortly there after. I'm just now getting around to getting it put back together. At the time I had Napa-bought radiator that was "correct" (more like a universal that didn't exactly fit correctly, however it was a HD radiator) and an an condenser from a company that was the largest they offered (made for SUVs, etc) and also used a PRO-6Ten compressor to replace the original a6. The car was put back to factory except those items, and I had the POA valve sent off and readjusted for 134a. This time rebuilding the car, I am going back with a factory original HD radiator, I will be adding the missing chin spoiler/air dam (helps with air channeling for cooling) and I"m hoping to find a more factory correct condenser.
The original engine was a 455 and had to be bored in order to correct the cylinders. I was warned the engine may run hot, however I didn't have problems with it unless it was idling with the A/C on. I did attempt everything you suggested and more back when I was working on the car to try to solve the original issue. I was advised at the time that a pusher fan was the best solution, however it may be worth seeing if the car will overheat with the factory correct style radiator and condenser first, though to be honest I doubt it.
 

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While a pusher may alleviate overheating at idle/ low speeds , it may well prove detrimental to cooling at highway speeds by causing turbulence in the airflow . Those BB GM boats very seldom had overheating problems in stock form. If I may ask , how much was it bored ? Have you checked for exhaust gas in the coolant ?
 

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Is it a thermostatic fan, they seldom work correctly after 70,000 miles, old age can kill them too. If it doesn't blow the hat off your head it is probably not working right.
 

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A proper clutch fan will cool a 455. For a while I had half a dozen using them in place of 454's in mud trucks/offroad piles.
Basically foating the valves followed by sitting then floating followed by starving the engine for oil.

If it is overheating your water pump is not circulating, cap not sealing, radiator is somehow blocked, fan clutch is not working, head gasket, or your not running a shroud.

The waterpump is the first thing I would check as they are often not replaced until everything else has been. A weak pump will still flow. But may spin less then it should.

The cap is the next thing. A bad cap will guarantee overheating and the current quality of replacements is junk. Pressure checking will show cap or headgasket in one shot.
 

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Discussion Starter · #9 ·
By mechanical fan, I mean a non electric fan. This engine was was completely rebuilt with all new components and has less than 10K miles on it. Al other components are new as well.
 

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Soooo , mechanical with the thermostatic clutch or without ? What was the overbore , .010 -.030-.060 ?? Is the radiator new or old ? Were the heads magnafluxed ?If you want to slap another fan on it. be my guest , but dont expect a lot of support from those who know the stock setup should be fine ..😁
 
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