Z06Vette.com - Corvette Z06 Forum

rbartick · 07-05-2002, 11:18 AM

I wanted to see what was going on with the stock fan programming so I started my Z06 in my garage, left the A/C off, and opened the hood. My garage door was open and the temp in my garage was close to 100 degrees F. The car was sitting for at least 2 days before this test so it was “cold”.

I first pulled the COOLFAN1 fuse. That disabled the entire low-speed circuit, as well as the driver side high-speed circuit. The car warmed up to 234 degrees and then the passenger fan came on in high-speed mode. It brought the car down to 226 degrees and then shut off. I let the cycle continue about 5 times. Each time the high-speed fan control came on at 234, and then turned off at 226.

I put the COOLFAN1 fuse back in. The low-speed fans came on at 226 degrees and then turned off when the car cooled down to 219 degrees. I let the cycle continue about 5 times. Each time the low-speed fan control came on at 226, and then turned off at 219. During this test the high-speed fans did not come on because the car did not get hot enough.

I put the AC on. The high-speed fans came on and stayed on for as long as I used the AC. They brought the car down to about 198 degrees in a few minutes. The car may have eventually gotten a few degrees cooler, but I turned the car off after about 5 minutes.

C5alive · 07-05-2002, 12:56 PM

That's interesting. Good test, thanks for the info.

Dave T · 07-05-2002, 01:01 PM

Thanks for the info.

sigung86 · 07-05-2002, 01:36 PM

I was having a a bit of a problem running hot in traffic the other day... 97 degrees and 2000 percent humidity. I turned on the air conditioner, and it took it down to operating normal. I remember a post from last year aabout running the AC between hard runs at the strip to cool your engine down much more efficiently....

Thanks for the information... like to be able to back up the old wives tales with scientific fact.

Now ... How to get rid of those warts on my hand ...

And see!!! Frank thinks I never pay attention!

Dan

rbartick · 07-05-2002, 05:11 PM

I just started the car while it was bone cold and I immediately turned on the AC in full auto mode and closed the doors and windows. The coolant gauge said 86 degrees F and the car turned on the low speed fans and it kept them on. I guess the car can command low-speed fans while running the AC. Sorry about the confusion.

The low-speed fans stayed on and the car got up to about 200 degrees. At that point I opened the doors and windows and put the AC on full blast, recirculation mode. Doing this raises the temperature across the AC evaporator. The increased evaporator temperature raises the low-side AC pressure. A higher low-side pressure will result in more AC clutch energized time and higher high-side AC pressures. The high-speed fans came on soon afterwards. The fans then cycled between low and high-speed at various temps in the 200-215 range.

I think when we run the AC the PCM chooses either low or high-speed fan control based on the reading from the AC high-side pressure sensor. A higher high-side pressure means the condensor is very hot and needs a high fan speed to exchange the heat and cool down. When I tested yesterday the ambient temperature in my garage was at least 100 degrees F. Today my garage was about 75 degrees F. The higher ambient temperatures yesterday were probably causing higher AC pressure. That would explain why the PCM requested constant high-speed fan when I turned on the AC yesterday.

PowerShifter · 07-05-2002, 05:37 PM

rb, I know there are more elobrate way's to control the fans but my method is quick and simple. Since you only need to run them in trafic or the stageing lanes at the track, what's the down side to doing the switch in the center compartment to energize pin 87 on realy 43? No codes or problems doing it that way on my last three C5's. Ric

rbartick · 07-05-2002, 08:31 PM

Quote:

Originally posted by PowerShifter
rb, I know there are more elobrate way's to control the fans but my method is quick and simple. Since you only need to run them in trafic or the stageing lanes at the track, what's the down side to doing the switch in the center compartment to energize pin 87 on realy 43? No codes or problems doing it that way on my last three C5's. Ric

I never really said that there is a down side to what you are doing. If it works for you then you should continue to do it.

The only thing I said was that I doubt you are running both fans in high speed mode when you hit the switch. Look under the car when you are in the 190-230 degree range and your switch is on (and AC off). I bet you find your passenger side fan is running high-speed, but the driver side fan is sitting still. Sending 12V to pin 87 on Relay 43 causes no difference in voltage potential across the driver side fan, thus no current flow. Check it out and let us know. You would probably have to look from underneath the car since I can't see the driver side fan blades from under the hood.