Nitro Junkie

My coolant temp usually runs about 198 F. Lately it has been cool, so I turned my AC off. Now the temps run aboout 230F, and the fans don't seem to come on. Is this normal?

Silvervettes

I have learned from this forum that the cooling fans will both run when tempurature reaches about 230 degrees per GM specifications. I was also concerned when the temp kept climbing on my C5 this summer while idling.

Read threads on this topic on this forum and you will find severals comments that I think you will find helpful.

Hope this helps.

C5-BRUCE

Here's some good information that I've archived. It should answer most of your questions.........

Both fans run in low speed and high speed. The fans are activated in low speed by the PCM when the coolant temperature reaches 226 F and switches them to high speed at 235 F. The high speed mode goes off at 219 F and the fans continue to run at low speed until the temperature goes below 217 F.

The way they do this is neat. The fans are connected in series with relay #2 between them. When the coolant get to 217, relay #1 supplies power to fan #1 and relay #2 passes it through to fan #2 and they run slow because of the high resistance of the two in series. When high speed is required, relay #2 switches it's output to ground, thus taking fan #2 out of the circuit and giving fan #1 full power. Relay #3 is activated to provide full power to fan #2. This is a lot simpler (and cheaper) than have two speed fans.

I found a wiring diagram that explains it a bit differently than the text version. Both fans run together under all modes. There are three relays wired to allow the two fans to run in series or parallel. When they are in series they have one power supply and their combined impedance causes them to run at low speed. When in parallel they each have their own power supply and run at high speed. The PCM monitors the pressure in the A/C system and turns on the high speed mode in which both fans run at high speed. There is no wiring scheme that allows only one fan to run. If only one fan is running then the other is broke!! (and the system should throw a DTC and not work at all).

Lovin It!!! - C5

Wow, good info.

rwj383

Fan 1 = ON @ 226, OFF @ 219.
Fan 2 = ON @ 235, OFF @ 227

robert
www.gen3motorsports.com

edensknight

Nitro Junkie

So I guess everything is working normally. With the AC on, the fans are running all of the time, so it runs cooler, eh? Makes sense.

Evil-Twin

Depends on the model year...
For later model years:2000 +
The low speed cooling fan is commanded on when the coolant temperature reaches 108°C (226°F). It is turned off if the coolant temperature lowers to 104°C (219°F). The high speed cooling fan is commanded on when the coolant temperature reaches 113°C (235°F). It is turned off if the coolant temperature lowers to 108°C (226°F). When the A/C is on and the coolant temperature reaches 85°C (185°F), the low speed cooling fan will be turned on at vehicle speeds less than 56 kPh (35 mph).

For early model years:
Low speed fans come on at 219,high speed fans come on at 228,low speed with a/c on...

both fans have high and low speeds...with the a/c on,the low speed fans will always be on regardless of coolant temps.Also,the high speed fans will also come on periodicly with the a/c on regardless of coolant temps particurly when sitting still.This is to lower a/c line pressures caused by no air passing through the condensor when sitting still.

0vetteshop