billschroeder5842

Can anyone shed some light on how this little guy functions on my 89?

I read through the FSM and found only a few references to the auxiliary fan mounted on the front of the condenser. It has 5 blades with no shroud. From limited reading, apparently there is a block sensor between #1,#3 spark plug that grounds at a certain (yet undetermined) temperature, but I have no idea.

I've never seen it work and don't even know if it does?

My main fan works as it should; it comes on at 226 w/o AC and runs continuously with the AC on.

Thanks!

v8vette84

Here is a link to a thread with a little bit of info.

https://www.corvetteforum.com/forums...corvettes.html

whitemj1948

In a nut shell, I removed my aux fan, I found that with out it the car runs cooler. The aux fan just blocks air from coming in, a GM fix (that did nothing) for owners complaining about the high operating temps. These temps were designed to meet emission standards at the time. PM me and I will explain what I did to keep the car running cooler. I have an 89 pushing 350 rwh.

billschroeder5842

Thanks, This is what I'm reading too...

I just shot you a PM

BlowerWorks

Yes - a stat on side of engine. Typically stat goes on around 240F. Replacing it with a 200 to 220 will help. The biggest problem with the C4 is at a standstill. If the front air dam has been damaged then the airflow is a short circuit. The AUX fan will help if set to come on earlier. I still have several stats for sale: $30 ea.

ex-x-fire

One issue I had was on a hot day stuck in Chicago traffic jam, the a/c would stop cooling. There's simply not enough air flow through the condenser & radiator with the single fan. I don't know if the aux fan would help in that extreme situation. Once I got over 30 mph the a/c started working.

mako41

This how it works for an '89. The main fan is controlled by the ECM it comes on when the coolant temp sensor hits ~228*F and off @ ~210*F. The Coolant Temp Sensor can be found below the thermostat housing.

If you have an auxiliary pusher fan in front of the AC condenser it is controlled by coolant temp switch found between cylinders 1 & 3 in the drivers side cylinder head. It comes on @ ~238*F and off @220*F. The auxiliary fan really helps cool down the condenser in hot summer months when the A/C is running full blast. The aux fan temp switch between cylinders 1 and 3 shorts to ground at 238 F, you can buy a temp. switch that turns this fan on at a lower temp (215*F) helping to keep coolant temps much lower than the factory 238*F parameter. Other lower coolant fan temp. switches are also available. When this switch is grounded the aux fan relay coil is energized which turns the aux fan on. If you remove this switch plug and short it to ground your aux fan should begin to run if everything is in working order. I wouldn't remove it if you run your vett in the summer with the A/C blasting!

As indicated above the ECM will turn the main fan on at 228 F and off at about 210 F. The main fan is turned on by the ECM based on inputs from the coolant temp sensor, vehicle speed sensor, and the A/C coolant fan switch. This ECM controlled main fan can also be programmed to turn on at a lower coolant temperature with either a tune or a eprom (chip) that plugs into your ECM. If you decide to alter the main fan temp. turn on point you should also consider installing a lower temperature opening thermostat to compliment the lower temp fan operating temps. 165*, 170*, 180* and 195* thermostats are available to do this.

mako41

Yes the aux pusher fan mounted in front of the condenser will do just that, as it pushes more air thru the condenser in hot summer months keeping it cooler so the A/C runs more efficiently. This extra air will also help the main puller fan suck more air thru the radiator to keep the engine cool. I don't agree with the poster above who removed his aux fan.... if you have one keep it in there and use it! Especially when blasting the A/C in the summer! In short the aux pusher fan cools the condenser helping your factory A/C cool much better than without it while the main ECM controlled fan cools your engine.

What I would recommend is installing a lower temp coolant switch found between cylinders 1 & 3 to get this aux fan spinning at a lower temperature to keep things much cooler, and thus avoiding heat soaking the entire engine compartment!

If you go that route these are your options;

AC Delco switch part # D1855B which crosses to GM part #14043275 can be ordered thru any Chevy dealer. It is a low temp grounding switch turning the fan on at ~ 215* F and off at 200* F (Much better choice for summertime A/C operation)

Not to be confused with the OEM switch AC Delco part# D1852B witch crosses to a GM part #14043276. This is the OEM Temp grounding switch that turns the fan on ~ 238* F and off at ~220*F (This is OEM & what you have now)

If your looking for more cooling MAM (Mid America Autoworks) does sell an even lower Temp switch which will turn on at at 200* F and off at 185* F, part #609-106

billschroeder5842

Thanks- this is exactly what I will do!

billschroeder5842

*update*

I ordered the AC Delco D1855B and it arrived over the weekend. I tested the Aux fan by grounding the pigtail--- it worked just fine.

I popped in the new sender with no real issues. I fired up the car and let the temp creep up. There was no leaks but the aux fan did not go on at 215. I watched the gauge climb to 226 and then the main fan went on as normal and cooled it down quickly.

Huh?

Did I get a defective unit? Is there a way to test the unit while still on the car like putting an ohm meter on the sending unit (the inside contact and the outside) and seeing if it is within specs?

BTW...The "sending shaft" that goes into the water jacket was about a 1/3 of the diameter of factory one, so clearly it is a different unit.

Any suggestions?

mako41

You sure you got the right part??
Did the Aux fan kick on at all? At what temp??

D1855B which crosses to GM part #14043275, which turns the Aux fan on at ~ 215* F and off at 200* F

Or did they give you an OEM part # D1852B witch crosses to a GM part #14043276. This is the OEM Temp grounding switch that turns the fan on ~ 238* F and off at ~220*F

Check your receipt and the actual part numbers on the switch.

billschroeder5842

The box said D1855B and the 14043275B. There were no stamps on the part.

No, the AUX fan did not come on at all. I double double checked the AUX fan and it popped right on when grounded. Since the only thing between the pigtail and a ground is the sending unit, I can only surmise that I got a defective unit or a mis marked one.

The photo on the AZ web showed that I got the correct piece for the lower temp. I ordered another one and will give it a shot.

billschroeder5842

Yes, that is an idea, but the factory AUX comes on at 238- YIKES!

I'm not sure I'm that brave

A Peter C4

Maco41 are you saying that if sensor wire is grounded that the relay will make the fan run ? This is something I would like to know. If this did work then I could ground it with a toggle switch, correct ?

mako41

Yes if you disconnect the single OEM wire running to the temp sensor switch found between the # 1 and #3 cylinders and ground it to any nearby grounding point the Aux fan motor should begin to spin. If it doesn't you have some other problem most likely the aux. fan relay is no good. On an '89 that relay is mounted on the drivers side of the radiator shroud. And yes you could also manually ground the relay with a switch to activate the aux fan any time you want.

mako41

Not sure what you issue might be, but keep in mind the ECM turns on the main fan with temp inputs from the coolant temp sensor found below the thermostat housing, temps in the drivers side head may not be exactly the same (I think they tend to run hotter), as these two fans operate independent of each other.

You must determine what temp the aux fan is being activated, the poster's above idea to disable the main fan until the aux turns on is a good idea. I would try it.

Let us know what you find.

billschroeder5842

Dumb *** question as I have no idea on how the sensor works in practice...

I'm about to swap my AC Delco D1855B for a Duralast SW505 that is supposed to be the same interchange with the AC version. As I mentioned earlier, I think the AC is bad.

So... I notice that the AC Delco version came with Teflon tape wrapping the threads while the Duralast that I picked up today had none and the factory one did not have tape either.

Could the Teflon tape effect grounding and make the sensor not read? Again I'm not sure how these damn things work.

Tod Stiles

No. the sealant won't affect the grounding of the switch. All that switch does is ground the terminal above 215 and then opens at 205 (or thereabouts) to turn the fan off.

WVZR-1

I believe the 215° is a very optimistic thought - original GM/ACD tolerances were quite close but that was 20+ years ago. I believe that the current packaged part is likely just a third party re-boxed and the most popular after-market that's likely in the box has a 221° +/- 8°

I doubt any of the "re-sellers" are paying for closer to OE design specifications.

JrRifleCoach

I added an aux fan on my 86 with little success. Not sure why it didn't help. Even tried moving it closer to the condenser which didn't help either.

Switching to the later two fan system might provide better cooling.