SoAlVette

Is it correct for the high speed fan to cycle while the a/c is running? I've read many posts here that state the fans run while the a/c is running, and to use that to keep the water temps down while sitting in traffic. Seems to work for me, but I noticed that my high speed fan will cycle, thus allowing the water temp on the digital gauge to go from 198 to 205 and back down in traffic, with the outside temp at 75 degrees. I am looking at adding either the 190 or 200 degree low temp fan kit which should eliminate the need for using the a/c for fan control. Will the high speed fan cycle with the fan kits also? Probably been covered here, but I can't seem to find any posts in search.
Here in Mobile, 90 plus degree outside temps are common in the summer, so I am trying to get prepared. Flushed and cleaned the radiator, made a huge difference, but I still would like to be able to stay in the 190 to 210 range in the heat of the summer

gerardvg

The cooling fan is operated independently to control temperature or gas pressure, the fan is activated by the ECM via a pressure switch on the refrigerant liquid line to control the pressures. Otherwise the ECM will try to keep the coolant temperature at around 230f the temperature where the engine burns fuel more efficiently.

The only way around it is a custom ecm chip or an aftermarket temperature operated fan cycling switch.

Paul Workman

It's a "C4" thing... The fans are ulitmately controlled by the ECM, and the ECM for the ZR-1/LT5 was initially an adaptation of the L98 ECM. So, for all things C4 ECM related, many of us ZR-1 pilots depend on Marc Haibeck or Cory Henderson, or Aron Scott to tweak the ECMs.

Marc Haibeck modified my 90 ECM so BOTH fans come on at ≈ 205ºF and turn off at about 200º (if memory serves), OR when the AC is turned on. I really like that.

For what you're going to spend on a temp sensor/fans switch, you could have the ECM program modified - a simple and elegant and reliable solution and avoid the kludged approach.

Anywayz... give Marc a call. Here is his BBB report and contact information (C-LINK).

P.

SunCr

a/c operation has nothing, but then everything, to do with Coolant Temp. When the Compressor is running, it's pushes out a high pressure gas that needs to be cooled into a liquid (in the Condenser) and that liquid needs to be around 100 to 150 degrees so that downstream, it can be pushed through a restriction into the actual cooling device, or Evaporator, at around freezing. In order to make that happen, the Main Fan has to run whenever the pressure or Temp gets too high; or turn off when it gets so low that it's making ice and plugging up the Evaporator (though there's a switch on the Low or cold side that will turn the compressor off if it is too low; the downside being that once it's off, you don't make cold air).

The pressure/temp of a compressed gas is instantaneous - there's no warm up necessary - so the Fan comes on sooner and to maintain the desired operating range, it stays on longer, then if it were off. Coolant needs to warm up (so there's a thermostat) and then maintain a range that keeps the engine from melting into a mass of molten metal and for emissions control, that's generally around 220 to 230 degrees. Absent a/c, which is exempt from Emissions, the fan is delayed until it gets these numbers, and runs for a much shorter time.

Difficult to beat the design built into Fan operation for a/c. The ECM relies on a device that tells it the exact pressure/temp of the gas and controls the Fan accordingly. Running the fan full time can chill the charge to the point that the compressor is off. Don't run it at all and it can blow a hole in the hood of your Vette.

At speed or around 35 mph, the fan or fans isn't necessary for anything and is usually disabled in the ECM.