When it comes to viscous clutches why is a thermal clutch best for A/C car?

Is the heat coming off the a/c condenser enough to engage the thermal clutch? I would think if you did an R134A conversion with an original condenser a clutch fan could be counter productive to low speed a/c cooling.

A/C puts more heat load on the radiator so the thermal clutch decreases the slippage to increase fan speed when a higher temp is sensed. A non-thermal clutch slippage stays the same regardless of temperature.

And don't store an OEM A/C clutch fan horizontally... at least not one for a 1965... keep it vertical or the fluid will leak out. DAMHIK.
- Art

Hmm, I think you had a bad clutch that had nothing to do with how it was stored. After all, how is is stored in the vehicle when not in use? Horizontally.

What position is the clutch in when you open a new box with the printing up?

Not just thermal but also Heavy duty is the correct one

um, i hate to bring this up, but when on the car, the fan and clutch are "vertical" [up and down]. horizontal is "side to side", like the horizon. unless, of course, you have the assembly off and tossed into the trunk [for storage] horizontally.

You see Nacho's post right above yours? That clutch is vertical. That is NOT how it's installed in the car. Rotate the centerline 90 degrees and that is how it's installed, horizontally.

please show a pic of one installed, then we can continue.
natcho's pic shows the clutch spring retainer and opposite side in the horizontal/side to side position. rotated 90* puts it at the vertical/up and down position, as is the assembly positioned on the car.

I'm just showing the front face of the correct clutch for AC cars, without any brass plate in front ( with or without thermal spring setup ), but the full aluminium disipation setup.

About the rest, I think this is going far out of any logic LOL. The horizontal position requirement is just while is storaged, not mounted. Once is mounted, the clutch is vertical no matter what!

Once is mounted that's not valid anymore. Spring will spin, thermal system will spin with fan and pump ( faster or slower, dragging less or more due the temp, doesn't matter ), so I'm not getting the deal of what you are talking about the spring "indexing"... or whatever else you are talking about! LOL

How do you think the clutch is mounted vertically? It's center line is horizontal not vertical, The mounting surface for the fan is vertical, but the clutch isn't.

Funny thing but I was also taught by my auto shop teacher in high school to always keep the thermal clutch fan in the vertical position just as it is installed on the car. We were also taught it will leak if not and I also believe I read it in a Mopar manual sometime over the 24 plus years I worked at a Dodge dealer. Will it leak if you lay it down ?? I don't know because I usually sit them in the same position as on the car only because I was taught that in 1972 in auto shop. Am I right ?? Good question but I can say they never leaked on me. Ron

On a side note...
Not sure if anyone experienced the same, but that Hayden clutch pictured did not work on a stock ('70 440) engine with A/C. The overall height of the clutch is very similar to the original "short shaft" clutches, however the distance between the fan mating surface and the water pump mating surface is less. This ends up placing the fan closer to the engine, nearly hitting the idler pulley. There was less than 1/8" of clearance, and this is with stock components.
I switched to a "456" repro clutch from Tony's. Sure, it's a lot more expensive, but at least it has the correct dimensions.

I didn't say that's the correct PN for the application, just posted the pic to show how does look the heavy duty unit for AC.

I remember have read on one or more of the clutches instructions sheets or packages I have bought about storage it horizontally. On the original package perspective is laying up or down, not the axis.

now I got what you meant, but still I don't think is about the axis/centerline.

So why after all this confusing discussion why do the EATON brand clutch fans I have in long term storage are clearly stamped 'STORE WITH THIS FACE DOWN' In other words the flat or thermal face down, I think I will follow the instructions from the manufacturer.

i most certainly agree with this, as is the center line of the crank shaft, alternator, water pump, and power steering pump. however, just like a flywheel and clutch/pressure assembly, the mounting position of these components are/is considered to be on the vertical plane. the center line of these components, however, is still in the HORIZONTAL plane, which is different than the mounting position.