99 s10 taurus fan

[rodder55]

okay i got a 99 s10 with the popular taurus fan swap. low speed works great but when i have my defrost setting on in my truck it triggers the ac high side of the fan. any idea on what might be the problem. i have the ac feed wire dioded and its feed off green one in back of compressor.

[MikeInCtown]

That would be normal. In an effort to extend longevity of compressors, GM and possibly others made it so that the compressor would cycle on when you turn on the defrost. (even when the setting was for heat) I suspect that you had the setting more towards cool, which would mean the car needs to manually cool the vent air, hence the need for A/C.

[Yogi]

It runs the compressor during defrost to dehumidify the air, which gives better defrosting results. As ambient temp. gets lower (50*F., I think) the comp. no longer comes on as the moisture content of the air is low enough that the dehumidification is no longer needed. However, the comp. will run anytime that you use defrost, regardless of temp. setting, as long as ambient is above 50*F.

[rodder55]

okay understandable how can i wire it to just come on when the ac is on only?

[MikeInCtown]

You can't. The defrost setting makes the compressor come on and the wire is the same. The computer is telling it to. If the compressor didn't come on, then you would get warm humid air steaming up your windshield when you turned on the defroster.

[rodder55]

okay will this pose a problem in the winter when i am defrosting my truck in the winter?

[MikeInCtown]

No, because the heat will be on. Even if the fans kicked on, it would be no different than if the stock cooling fan was pushing cold air at the engine. Are you just worries about the fans running, or that the compressor kicked on?