Probably a dumb question, but would that mean that it would only turn on if the AC compressor is engaged?


Another dumb question: I flushed the original radiator out of the car and stupidly left the nipples for the trans cooler uncovered allowing water in. I just had the trans rebuilt, definitely not willing to risk that $3k job over a $200 rad. Could I flush the trans cooler with some DEXIII before hooking the part back up while I wait for the new unit?

The compressor would have to be on long enough for the refrigerant temp to reach the point needed to trigger the fan switch. (The fan will continue to operate if the compressor is switched off, provided the refrigerant is hot enough.)

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I see. So assuming the ambient temp isn't requisite of using the AC (just cool air blowing has been sufficient so far this year) then the engine shouldn't have any need to use the aux fan... Am I thinking this correctly? Furthermore, there would be no signal for the fan to ever turn on without the AC compressor engaging, right? Does anyone ever bypass and add in a manual on/off switch for it?

If that's the case, then I'd definitely have something wrong as I can't imagine I should be dealing with escalating temps when we're still in windows-down weather.

It's clear to me that the aux fan was intended to benefit the A/C condenser, not the radiator.

I drive an '82 300D in Augusta. I haven't seen a coolant temp over 85º C since last August. Under the most adverse summer conditions, I never see much over 95º. A serious uphill grade on a 102ºF humid day might approach 100º C.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

A manual switch can be installed in parallel with the refrigerant temperature switch located on the receiver/dryer. It is easy to attach because the switch has 1/4" spade connectors and there are adapters.

The compressor would have to be on long enough for the refrigerant temp to reach the point needed to trigger the fan switch. (The fan will continue to operate if the compressor is switched off, provided the refrigerant is hot enough.)

That's no major issue. I would stand the radiator on end and let it drain overnight, then blow some low pressure air through to dry out the cooler.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

The compressor on and refrigerant temp (receiver/drier metal, actually) above 62 C. If you are using R-134a then that is too high for good cooling. Lower temperature switches are available. These can be swapped with out refrigerant loss. The fan will run after the compressor is turned off until metal of the receiver/drier where the switch is mounted drops below approx 62 C.