Can the on/off settings be gotten to through the DIC? I know it can be done with a programming device but is there a hack for doing so without one? I know that there are secondary functions accessible by combination sequences with the DIC buttons (such as recalling diagnosis codes)...

I'd like to get the fans blowing a little sooner when driving in bumper to bumper, the coolant goes up to 210-215 degrees in stop and go.

 

I have never heard of the way to set the settings via the DIC. The fans are set to come on at 225 from the factory, temps of 215 are not out of the normal. Only was to change the setting is by programming the computer. Most tuners can do it. Did not look at your profile, so do not know if you have enough mods to require a dyno and tune.

 

Purely stock set-up. I know that I'm still well within design tolerances but the heat build-up in the ****-pit is noticeable. I'm hoping someone knows a hack, otherwise I'll just have to get it done next time the care requires a mechanic. I can't see buying a predator, etc. just to change the on/off points for the fan. I don't want to mess with my set-up otherwise; if it ain't broke, don't fix it.

 

And if the fans aren't broke ... don't fix it.

The heat build-up in the cabin will not be affected by the fans. Most of that heat comes fronm the exhaust system under the car. If you do a search for "tunnel plate" and/or "insulation" you should find several topics about things that can be done to change this.

 

That's not going to fix the heat build-up; that's due to no air flow under the car and the exhaust heat migrating into the cabin.

Best thing to do is turn the AC on and direct it to your feet.

HTH, and have a good one,
Mike

 

Your points are well taken. I was hoping to make this smaller modification to reduce, even a little, the heat-sinking effects, be they exhaust gas temp or engine block temp in origin. My thought was: Drop the operating temperature, drop the radiant heat.

BTW, wouldn't running the A/C in bumper to bumper traffic increase the load on the engine and raise temperatures even more?

 

No. Just the opposite. Turning on the A/C (Why would you ever want it off?) reprograms the fans to turn on at a lower temp.

 

If the following conditions are met ...

* Coolant temp over 185 F
* A/C compressor is ON
* Vehicle speed LESS than 35 MPH

Then the PCM commands the cooling fans to the LOW speed setting. This helps air flow through the A/C condensor, and also keeps coolant temps down. If the above conditions aren't met, the PCM will let the coolant temp rise to 226 F before commanding the fans to LOW speed. Coolant will have to reach 235 F before th3e PCM commands HIGH speed operation.

GM Powertrain spent millions of dollars and thousands of engineering hours determining the best operating temperature for your engine, based on issues such as power, fuel mileage, and emissions. If you know better than they do, go play with the cooling fan settings.

 

OK, so if I run the AC when travelling at low speeds, I'll actually get the advantage of lowering the threshold for cycling on the fan. That's cool and makes sense when I think about it- GM took a counter-measure to off-set the increased load.

Now the $100,000 question: Would I be stressing either the HVAC or the cooling system by running the AC in bumper to bumper WITH THE TOP DOWN? I don't but I might if it made a positive difference. Most of the time, if I'm driving the 'Vette it's because we're having convertible weather.

Thanks to everyone. If I knew better than the GM engineers, I wouldn't be asking any questions, I'd already have my answers! But, I do know that engineers try to work compromises into their solutions, there's always room for change.

 

Just my .02, but.... your post about... "turning on the A/C makes the the fans turn on at a lower temperature" is...... totally incorrect. When the A/C is turned on, IN ANY VEHICLE EQUIPPED WITH AN ELECTRIC FAN(S), not just a C5, at least one of the two fans (If the vehicle, like our C5's, has two separate fans.), or the single fan, if so equipped, is virtually IMMEDIATELY engaged. Why? Because the compressor, while acting as the "heat pump", also increases the pressure in the system. This pressure rise is EXTREMELY rapid if there is no airflow through the condensor-I have seen some A/C lines rupture within 30 seconds on a vehicle where there was no engagement of the fan while at idle. When you start your car, even in the desert at 120 degrees ambient temperature outside, it still takes the motor several minutes/miles to reach 200 degrees in the coolant deptartment- the A/C would not have time to wait for the coolant temps to signal the fan to operate!! While in Las Vegas last year, the reading on my C5 HVAC readout showing outside temps showed 120 in the downtown area around 3:00 PM. In stop and go driving, my A/C would start shutting off and on, due to the high pressure switch protecting the system from impending doom, EVEN WITH BOTH FANS RUNNING!!

 

No, you will not stress the system. I seldom have the top on and use the A/C only in heavy traffic. It keeps the engine cooler and if conditions are right keeps me a little cooler. I have been doing this since 1998 with no problems.

 

Grinder11 ... I'm afraid you're the one who is incorrect ..... direct quote from the GM Service Manual for the C5 ....

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).

You can prove this to yourself ... go out to your car and start the engine. If the coolant is below 185 and the A/C is ON ... the cooling fans WILL NOT RUN. Watch your temp gauge and when the coolant reaches 185 ... voila ... you'll see the cooling fans start.

You may want to have someone check your A/C system. GM has a test facility outside Phoenix that tests cars for hot weather performance. Your A/C system should have been OK, even in those brutal conditions.

 

Thanks for all the info. I'm going to try running the AC when I'm creeping at rush hour and see what difference it makes. I know the old trick for bleeding heat off the engine by running the heater, but that WON'T do. If running the AC with top down isn't taxing anything (other than my wallet), I'm game.

 

My only contention to the point about GM engineers knowing more is that their mission was to find a happy medium of performance and still pass emissions testing. This is contradictory to many of us performance-minded guys. Bottom line, a cooler engine with cold air induction will perform better in terms of HP/TQ, not in terms of emissions!

Let's not get into oil viscocity and breakdown! LOL

 

Actually, a hot engine with cool intake air is the best setup for HP/TQ. Want proof ?? Take a look at the engine temperatures used in race cars today. Most engines run 230 degrees on the track for max HP and Torque, with Formula1 engines (and their special fuels) running even hotter than that.

When you burn a fuel in an internal combustion engine, you are converrting the energy stored in the fuel into 2 kinds of energy. About 1/3 of the energy produced is lost as heat energy out the exhaust system. About 1/3 of the energy is lost as heat energy radiated into the engine itself (pistons, cylinder walls, heads, valves, etc.) and the remaining energy is mechanical energy that drives the piston in the power stroke. By keeping the engine parts as hot as possible, less energy is lost to heating the engine, and therefore more is available as mechanical energy.

In an "ideal" internal combustion engine the engine itself would be at the temperature of the burning fuel, which would mean you would get even more mechanical energy out of it, but with gasoline as the fuel, the engine has to be cool enough not to pre-ignite the fuel during the compression stroke.

The GM engineers (and race engine engineers) have tried to maximize the engine temp not just for emissions, but because they understand what generates power.

Hope this helps,

 

If only our blocks and pistons were made out of space shuttle tiles (the ones that didnt fall off ) we would be making a lot more power and better fuel mileage.

To the op, just get a tune or a handheld tuner to lower the fan on temps.
Also for the AC question. Even with a stone cold enging, if you start the car with the AC on, the fans will come on when the head pressure is high enough to activate them........driving or not. Usually the fan wont come on right away until you start removing heat from the cabin via compressing the freon and circulating it, or high rpms with high blower speeds.

 

Nope, the A/C system has a Refrigerent Pressure Sensor monitored by the PCM. If refrigerant pressure is higher than 410 PSI, or less than 30 PSI, the PCM will dis-engage the A/C compressor clutch.

The PCM controls the fans based on engine coolant temp .... nothing else. If refrigerent pressure gets too high, the PCM shuts off the compressor until line pressure is back within the "normal" range.

The PCM is "all powerful" over the A/C compressor .... an interesting side note .... when the compressor is requested to ON by the HVAC controller, the PCM actually increases throttle on the engine to overcome the "drag" of the compressor when it first is clutched to on. That's why yoou don't feel (or feel very little) the classic "hesitation" in engine power as the A/C compressor comes on line. Pretty clever, huh ???

 

I can't think of the company name (VINCI?) that sells a plug and play product for limited fan on/off adjustments w/o a professional tune.
I've recall some members who've said they use it successfully.

 

That is just plain stupid. What if I want to start up my car on a 90 degree day and go 40 mph with the ac on high but there is a 40 mph tail wind? Whoever designed that is a moron. That means that until the engine temp reaches 185 I will have no ac since the system would shut down the compressor as the head pressure gets high with no airflow? Almost every other car around has the fan come on at a certain high head pressure.

 

I just went out to my car at lunch in the parking garage and started it and turned on the ac to max. Kept it at 2000 rpms and the fans came on before 138 degrees on the DIC for coolant temp.