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Controlling Electric Radiator Fan

69-er on Fri June 01, 2012 1:49 PM User is offlineView users profile

Year: 1966
Make: Chevy
Model: C10
Engine Size: 350
Refrigerant Type: R12

I will soon be converting my truck's mechanical fan to an electrical fan. I am trying to come up with a way to control the fan when the AC is on. I know I could simply have the AC system turn the fan motor on anytime the AC is on, but I want to go a step further. (I don't want it to run full time) This is a factory system. It's been several years since I last worked on the system, but I beileve it uses a thermostat at the evaporator to control the comperssor.

Ideally, I would like it to turn off at speeds of 35 MPH or so higher, or at least when the system does not require condenser airflow, (maybe by monitoring pressures?). I've seen various electronic fan controllers on the market but I'm not sure if they take into account the system pressures.

Would a trinary switch perform this function for me? If yes, can I find a wiring diagram anywhere? It seems like I remember the RVs I used to work on had trinary switches. The only problem I see is if the switch waits untill the pressure changes enough to indicate condenser air flow is required, it's already struggling to get the temps back down.


Edited: Fri June 01, 2012 at 1:58 PM by 69-er

emsvitil on Fri June 01, 2012 7:29 PM User is offlineView users profile

I just trigger the fan with a relay when the AC compressor is on.


NickD on Sat June 02, 2012 5:11 AM User is offline

Does that 1966 have a fan clutch? Was mostly an option back then and a piece of crap. Even my 82 454 has a fixed fan, beside the radiator, condenser, has a huge oil, tranmission, and a PS coolers in front of it. I don't have any cooling problems with it.

Really doubt if your stock alternator has the power to run an electrical fan, then between the engine and that fan, its only 30% efficient, a fixed fan is 100% efficient. Need the most cooling at idle, when your alternator is least capable at those low speeds of producing that power. At highway speeds, a fixed fan uses very little engine power due to the windmilling effect. Besides a fixed fan, also need a radiator shroud to put all that air through the radiator. Without a shroud, just kicking air in circles.

When FWD's came along, we had to make an alternator that could handle it cheaper than the old conservative designs, overheating was a major problem, and 50 amp alternators were out, had to be 100 amp alternators, then all that control circuitry that caused even more problems. A major step backwards. You will not see any increases in fuel economy with an electric fan, if anything, a decrease in fuel economy and performance.

Why go backwards?

GM Tech on Sat June 02, 2012 7:58 AM User is offline

Originally posted by: emsvitil
I just trigger the fan with a relay when the AC compressor is on.

Yeah Dawoo tried that on a Mitsubishi Delica SUV in Taiwan...then whenever the system shut down for high pressure cut-outs-(90+ temps)- the fan quits too-- just when you need it most!!

And with no diode in the circuit, the fan will hold the compressor clutch (as it slows) in until 6 volts or so-- and you get to listen to that hissing/slipping sound everytime you shut off the engine.

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Sat June 02, 2012 at 8:00 AM by GM Tech

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