Mine has come on at 228 since it left the Dealer showroom back in '89. GM issued plenty of Service Bulletins correcting Manual mistakes - hopefully you've got them since one corrects intake gasket installation - but there's nothing on the temp specs.

They did issue a Bulletin in '85 about the Aux Fan announcing it as a Dealer installed option following complaints from Autocrossers and High Altitude users. That's all it was meant for, though making it a Factory option added an additional $100 to the Sticker price and I'll presume $90 of that was profit. Notably, more Vettes left the Factory with the HD radiator option and without the Aux Fan. Guess some Dealers valued volume over airflow.

Unless the harness is new, I'd be inclined to suspect there's excessive resistance in 22 year old wiring, particularly in the engine compartment, as opposed to some misprint. But, these discussions should be more about why the system, with one fan, isn't performing at Factory specs. For an '89, that often means a mucked up system, often because the head gasket is weeping/leaking, but there are plenty of other reasons.

 

Are you saying your auxiliary fan comes on at 228* F?
What temp does your main fan come on? It's supposed to come on at 226* F. If your auxillary fan is coming on at or near the same temp something is not right, they should't both be coming at the same temp!

I realize the ECM controls the main fan using temp. input from the CTS sensor below the thermostat housing and the auxiliary fan temp. switch between the no. 1 & 3 cylinders controls the auxillary fan and that these temps are probably different but both fans should not come on at the same temp.

The OEM auxiliary fan temp. switch GM part no. 14043276 is rated to close at 238* F always has, always will!

 

Fixed.

On mine, the temp is usually about 10-deg difference. When the dash says 238, the ECM might be showing/seeing 228.

For the main fan, a turn-on around 225-225 might not happen until the display shows in the 235 range. That's because it would be lower at the CTS sensor.

 

My Main is on at 226. Aux is 228 and never comes on. When the Main comes on, the Temperature drops (as it should with any cooling system). To test the Aux, I put the nose up against the garage wall to block air flow and turn the a/c off. It's been that way since it was new and it bugged me that there was this fan sitting there which didn't seem to be doing much of anything.

Since '94, cars with Aux fans use them to cool the a/c charge (R134) which because if it's smaller molecule, can make incredible pressure at ambients above 90 degrees. Before then - like in '90, the engineers began to ramp up for the change over and the C4 got a second fan controlled by the ECM with same coolant temp parameters (226/228), but primarily uses that 2nd fan when the compressor is engaged. Pressure is temperature and the bogey for the liquid in the Condensor is a range of 100 to maybe 140 degrees under all conditions. Let the temperature/pressure spiral out of control and it'll blow a hole in the hood long before the coolant overheats.

Late model C4's use two speeds - some of the Asian vehicles, like Toyota, use 3 fans - but all will only be cranking with the a/c on.

We're 30 plus years now into electronic fuel injection and catalytic converters and at least half that much with these a/c systems. Cats are most efficient with idle/low speed coolant temps in the 220's. A/c operation is exempt from Federal and State Emissions and the primary function of the cooling fans is to keep the a/c working safely when it's cranking. To do that, the fans come on sooner and stay on longer with the resulting benefit being lower coolant temps.

 

Seems like you sent me a PM on this topic in early 2010. IIRC, your advice was to run my car w/o having the AUX fan hooked up. (Maybe I had also indicated I'd purchased a lower fan switch and built a 383?)

At the time, I couldn't understand why you'd made that suggestion. Now, I think I understand. Because my AUX fan turns on too low, it runs all the time. That means it's blowing across the condenser coils all the time. When, I turn on the A/C, the condenser gets hot and that hot air adds to the load on the radiator. This has to be a problem.

I wonder why they didn't wire the AUX fan to turn on when the high pressure switch was activated?

Because the compression with my 383 dictates the need for lower coolant temps, I now see why having the main fan run -- W/O the aux fan adding add'l heat load -- is the best approach.

If my coolant temps never went above 210 on a hot day, would it be possible for the condensor overheat (per se)? If I understand you correctly, the pressure would get too high first and the high pressure switch would take care of any A/C overheating issue.

Am I on track? Should I unplug the aux fan relay and see what happens?

 

Whaddya know! I still have that PM in my inbox....

On 6/11/2010, my question to you (while still thinking you might be a GM technician) was....What should I do with the AUX fan after building a 383 w/higher compression, higher flow water pump, 180 stat, and the ability to program the ECM? I asked if MAYBE I should buy a 200-deg AUX fan switch.

Here's what you said...

But, I wasn't sure this reply made sense. First of all, I couldn't understand how you could "overcool" the charge too much -- on a day hot enough to run the A/C!

I also didn't understand the comment about soaking up heat in a parking lot. Again, how could a fan hurt? If the condenser got hot from parking lot heat, why wouldn't you want the AUX fan to run (even though it wouldn't run until the engine got hot enough). By the middle of your reply, I was thinking..."Hmmmm....Maybe this GM tech doesn't get performance questions much." LOL

By the end of your reply, I wondered....Does cooling fan mean "Main fan"? If so, what could "blow up" if I guessed wrong?

At the time, I thought about getting clarification on the questions above. But I thought I might find the answer before my engine was complete. In the mean time, I never deleted that reply. Turns out I never figured it out....except that I'm starting to think your recommendation to "start by leaving the AUX off" was the right one.

Hence, the reason for post#25.

 

 

Damn devil-weed will do it to ya every time!

BTW...If something's freakin' you out here, feel free to say who, what, when, where, or why!

 

Basic a/c - Meter a liquid into the Evaporator around freezing by starting with a high pressure/temperature liquid and then using a restriction to drop it's pressure/temperature. Pressure/temperature is determined/fixed by volume (size of the lines and component parts and air temperature. To maintain consistency over a wide range of ambients, cool/heat the liquid by regulating air flow across the Condensor; ie, with the Fan or Fans or force feeding it while driving by exposing it directly to the air mass. Not enough air flow and the liquid will get too hot (pressure too high) to meter at a temperature/pressure close to freezing. Get it real high and it will blow up. Get it too low, and it will make ice cubes with the latter being prevented by a low pressure cutout for lower ambients (generally below 50 degrees).

Compressor is no different than an engine and what's going on in the Condensor is only different from a radiator in that it's receiving a high pressure gas and the air flow cools or condenses it into a high pressure liquid.

Basic automotive R12 design is engineered to maintain average high side pressures of around 200 psi (138 degrees, though more like 120 with subcooling) and keeping it there pushes 28 to 30 psi (29 to 32 degrees; 36 to 40 degrees with superheat) liquid into the Evaporator, though realistically, you will only hit this design spec for a temperature range of 70 to maybe 95 degrees. Above or below these ambients, you'll get less/more, but it's the target number and it works quite well for anything down to 0 or over 100.

Since the Condensor operates at a lower temperature than the Coolant, it's in front of the Radiator and a thermostat is used to control Engine Coolant temps.