"A/C electric fan on when A/C Clutch on"

Scorpio / Scorpio Cosworth Discussions - Questions, problem resolution, general talk, technical tips and modifications.
john keefe
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Re: "A/C electric fan on when A/C Clutch on"

Post by john keefe » Sat May 04, 2019 2:49 am

RockAuto has both, but they're back up to the high $30's. Still a good deal, just wondering if they were worth it, but I guess they're better than the OEM

taylor0987
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Re: "A/C electric fan on when A/C Clutch on"

Post by taylor0987 » Mon May 06, 2019 10:40 am

To keep on the tangent about the engine cooling, I just replaced my fan clutch. There sure is a lot more air flowing!
I got the Hayden which was the cheapest on Rockauto at the time I ordered.

Ed Lijewski
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Re: "A/C electric fan on when A/C Clutch on"

Post by Ed Lijewski » Mon May 06, 2019 12:56 pm

FWIW: I just decided to look into GMB a bit. Their Social Responsibility caught my attention. I'll buy GMB again.

https://www.gmb.net/about/

YMMV
Descartes: "Cogito Ergo Sum"
Lijewski: "Sum Ergo Drive-O. Mucho!

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Re: "A/C electric fan on when A/C Clutch on"

Post by brokencase » Wed May 08, 2019 10:44 pm

taylor0987 wrote:
Mon May 06, 2019 10:40 am
To keep on the tangent about the engine cooling, I just replaced my fan clutch. There sure is a lot more air flowing!
A new fan clutch can howl the fan a bit as it first breaks in.

More interesting is the subtle interplay between the set point of the thermostatic clutch and the thermostat in the cooling system.

For example...If I install a 185F thermostat in the cooling system - What happens to the behavior of the thermostatic clutch fan?

Take your time...think it through...

john keefe
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Re: "A/C electric fan on when A/C Clutch on"

Post by john keefe » Sat May 18, 2019 2:03 am

OK... I'm gonna' guess it will depend on the temp activation point of the thermostatic clutch (TSC). E.g., if it's 185 and the original A/C thermostat generally activates the fan at a higher temp (sans special activation modes for icing, etc.), then the TSC is engaging until the A/C drops the post-radiator temp below 185. So, unless it's boiling hot outside, a lower temp A/C thermostat would keep the post-rad temp at or below 185 more often, proportionally reducing the time the TSC is engaged for temps above 185. I'm sure there's a more succinct way of expressing it, but that's out of my wheelhouse at the end of a long week of construction.

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Re: "A/C electric fan on when A/C Clutch on"

Post by brokencase » Mon May 20, 2019 12:03 am

In this instance I was not referring to the A/C system. Just the cooling system.

So what happens is the clutch fan engages more often because the radiator must reject more heat to keep the engine at 185F.

When it is cooler ambient its not an issue, but when it gets warm out I can hear the fan howling and I can feel the loss in power.
Of course it's even worse when you turn on the A/C.

But the "A/C electric fan on when A/C clutch on" mod helps this situation.

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Re: "A/C electric fan on when A/C Clutch on"

Post by john keefe » Tue May 21, 2019 2:54 am

Ahh... I gotta' think that through a little more, or I've got my perception of the system a little off.

In the Scorpio, the TSC operates independently from the A/C and the thermostat. The thermostat and other calculated variables determine when the A/C fan comes on. Doesn't matter what the engine temp is, or the temp in front of the radiator, it's what the TSC "sees" around it (convected engine bay heat) and post-rad air temp that it will react to.

Say the TSC engages at 193 degrees post-rad temp, and the "stock" thermostat switches on at 195 degree, the engine temp is 185 degree, and the convected engine bay and post-rad air temp is at 190 degree. Again, and just for this example, doesn't matter if the engine itself is 185 - 196 deg, the TSC is not engaging until the convected bay and post-rad air temp reaches 193 degree.

But, if the A/C fan switches on at a lower temp (185), you suddenly have a larger mass of heated air passing through the radiator at a velocity. The coolant temp is radiated/convected to the air mass, reducing the coolant temp but proportionally increasing the temp of the air mass. So, the post-rad temp is now increased, probably to over 193 deg., and the TSC engages when it otherwise would not.

So, that's how you unintentionally reduce the life of your TSC. That what you're seeing/thinking? Do I get a prize? :D

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Re: "A/C electric fan on when A/C Clutch on"

Post by Ed Lijewski » Tue May 21, 2019 8:24 am

The bi-metal spiral actuator in the fan clutch couldn't have a precise on/off point but rather an actuation range of e.g. 10*-12*, just as the XR coolant fan sensor does (it works via an internal bi-metal disc which changes shape from convex to concave to establish a ground circuit). Same holds true for the internal fan clutch fluid.

YMMV
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john keefe
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Re: "A/C electric fan on when A/C Clutch on"

Post by john keefe » Wed May 22, 2019 12:42 pm

Good stuff, Ed. But, do I still get a prize? :D

Ed Lijewski
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Re: "A/C electric fan on when A/C Clutch on"

Post by Ed Lijewski » Wed May 22, 2019 6:03 pm

You've always been a winner in my book, John.🎯 👏

YMMV
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john keefe
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Re: "A/C electric fan on when A/C Clutch on"

Post by john keefe » Thu May 23, 2019 4:07 am

I'll take all the compliments I can get. Grazie

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