Ok i have read and read about cooling fans but i guess im gonna double check myself.. i have a 89 l98 6 speed... the problem is when the A/C is on teh car gets hot.. i have a super chip in it which kicks the fans on early.. the main fan teh one in front of teh water pumps operates as it should.. its teh auxil fan that doesnt.. i jumped teh relay on teh fan shroud and it comes on... i unplug the single green wire with white tracer from the temp sensor on left head between cyl 1& 3 and ground it .. its comes on.. WTH !! i have replaced teh sensor with 2 diff new ones.. still the same result . it was my understanding that the main fan with the relay on teh fenderwell is ecm controlled and the aux fan is the temp sensor on teh head controlled.. am i missing something or am i just getting bad sensors ??

thanks in advance

 

Aux fan has nothing to do with a/c and isn't needed for much of anything anyway if the system is right. A/c uses a switch on the high line that signals the ECM to ground the Main Relay. It does this by opening at 230 psi. You can simulate the open by disconnecting it which should turn on the fan. You'll need a Manifold Gage Set to see if it's working right. Assuming it is, the system is plugged up - you'll see extremely high pressure on your gages (like 300 psi or more) - Or, air flow is restricted - Or the Radiator and cooling system is plugged up and the load of the a/c system puts it over the edge. When it's right, Coolant Temps will be 10 to 12 degrees lower with the a/c on as the Main is on sooner and stays on longer to maintain the correct pressure (and the gas has a temperature well below the thermostat) and cold air flowing out of the vents. Running the fan too long or with the Aux fan can push the Pressure too low and the compressor will cycle more frequently which creates unnecessary wear (and sometimes a crappier idle because until '90, it's not controlled by the ECM). Best to leave it at the Factory Limits, but you've got to get it back to that first. Get a gage set and check it out.

 

IIRC Aux fan runs @ 238F
Is engine getting this hot without Aux fan run?

 

engine is getting hot as in 240 and the aux fan does not come on.. i understand the a/c not controlling the aux fan .. but when its 80+ out the a/c running will make the cooling system work harder.. this is while sitting in traffic .. if i jump the aux fan switch and it comes on it cools back down as it should be and runs around 225

 

also... regardless of if the a/c is on or not.. as it doesnt control the aux fan .. the aux fan SHOULD come on when the ehgine temp reaches the set temp.. a/c on or a/c off it doesnt know it just knows a temp seting ?? right ?

 

According to what I'm seeing in print the aux. fan switch in the left cyl. head closes and becomes a ground for the relay at 228*. You've proven the circuit/relay and fan are good. Assuming the sensor you're buying is the correct sensor for your application--then it's possible your temp gauge may not be accurate. A infared laser thermometer would be useful because you could see what the temp actually is at the aux fan switch. You could also check temp. at radiator and water pump etc. As i said you may not be running as "hot" as you think you are. Your statement above is correct the aux. fan switch is the only thing which turns the aux. fan on/off.

 

The aux fan switch between cyl 1 and 3 shorts to ground at 238 F! This grounds the aux fan relay coil and turns the aux fan on. The ECM turns 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.
You have to expect higher coolant temps with the A/C on because the condenser ahead of the car radiator warms the air before it gets to the car radiator. It is a good idea to clean all debris stuck in the condenser AND the car radiator. C4's pull air in from the bottom front and pick up all kinds of fine road debris which sticks in the radiator fins near the bottom and decrease the radiator area.

 

there is NO debris issues.. so im leaning towards bad sensors.... i plan on taking it to my buddies shop and hooking it up to the scanner to verify the temps.. but owning the car 12 years now,, i dont think the gauge is off.. the car runs VERY strong between 160 and 180.. still does.. after 180 you notice a decrease in power.. and usually the car runs around 178 - 185 so i can only assume the sesnsors are not right .. i mean after all you ground out the wire and the aux fan comes on and the car cools off..

 

The specs I'm seeing online are 226* ECM controlled (primary) fan on.
The auxillary fan temp. switch closes at 228* and turns on the aux. fan.
I didn't write these specs, I'm just relaying what I see online.
"jfb" and "vetteoz" very well may be correct at the 238* for the aux. fan on a '89 and the specs I'm looking at are incorrect--- 236*-238*-- IS correct for the secondary fan on later C4s where both fans are controlled by the ECM.

Regardless of which spec is correct the coolant in the cyl head between #1 and #3 is not getting hot enough to close the fan switch IMO-- Since you're SURE because you've owned the car for 12 years your gauge is accurate and you're "leaning towards bad sensors" (switch) it sounds to me like you were just looking for confirmation from the members. So keep replacing the sensor (switch)--maybe you'll get lucky.

Since the radiator is clean outside maybe-just maybe it's partially plugged internally causing poor flow and hot and cold spots in the cooling system. Once again a infared laser thermometer would be useful. When you find your problem--post up the fix--don't just let the thread drift off into oblivion--like so many threads here do

 

does anyone know if BWD part #TFS5 is the correct switch ?? does anyone have the correct part number in gm or standard ect ?? something i can cross reference ??

 

Aux.fan temp switch OE p/n--14043276

coolant temp. sensor OE p/n--15326386

 

An idle/low speed temp of 205 to 212 is more typical for a/c any ambient; any car including your Vette. There's always the possibility that you Display is inaccurate. Compare it to the Coolant Temp Sensor with a scanner. If it is accurate, you need to look into it further. 89 non a/c specs are 226 primary; 228 aux. When the Main Fan comes on, it's suppose to drop the temp - if it doesn't, it ain't right. Lot's of Vette's left the factory with only 1 Fan and had no problems with coolant temps.

 

OK sorry its been awhile between posts here .. This is what i have figured out on this issue and also a nice fix for it !! i recvd MULTIPLE bad bwd temp swithces... from a parts supplier.. these were not turning on the aux fan as i had said above til well over 240 !! did some research and found that BWD makes a TFS4 .. bought it online and installed.. tfs4 turns on at 215 and off at 205 .. Much nicer car now runs max 220-225 in traffic super hot day with ac on .. not sure of the application but its a nice fix and works great !!! i bought mine off ebay for under 15 bucks.. i believe autozone can special order the switch but doesnt stock it ..

hope this helps some other folks on here

 

I see this is an older thread butif anyone is interested, I wired both fans to come on with the key. They stay on ntil the key is turned off with relays that keep them running about 5 seconds after the engine is off. Car never runs over 200 degrees, I live in Florida so it is always mad hot and the A/C is always on.Get about 19mpg on my 89.

 

The infomation in post#2 (above) doesn't compute.

A) If the aux fan doesn't have anything to do with the A/C system, why go into detail discussion about it?

B) The HP switch for the A/C triggers at 240PSI. From the schematic, it appears the ECM monitors the pressure switch. It does not appear to create a ground FOR the fan relay. (It is, however, grounded to the same junction block.) I would assume the pressure switch provides independent operation of a fan to cool the A/C system. (IOW, I'm guessing it can trigger the aux fan when PSI gets too high.) Since the ECM controls the main fan, I'd expect the main fan to also run with the pressure switch is high enough to close (at 240PSI).

C) I purchased a lower temp aux fan switch (located in the DS cylinder head). It is designed to trigger the aux fan at lower temps. As described, mine triggers the aux fan by 200-degrees. The HP switch does not have to close for this trigger to occur. My aux fan runs most of the time now. And, A/C is cold, cold, cold.

 

My 89 FSM says 228F.

 

GM part # for the OEM auxillary fan switch mounted between the 1 & 3 cylinders is 14043276 (AC Delco # D1852B) This switch closes at 238*F and opens at 220*F

GM part # for a lower temp switch that closes at 215*F and opens at 200*F is 14043275 (AC Delco # D1855B)

Mid America sells an even lower auxillary fan switch that closes at 200*F and opens at 185*F, part # 609-106

 

I believe the ECM closes the main fan relay at 228*F. The auxillary fan temp. switch found between the 1 & 3 cylinders closes at 238*F. This is for an '89 L98 right from my service manual.

 

Interesting....According to my '89 FSM, it says 228 on the schematic for the AUX fan. Maybe that's a misprint. Were you looking in the service portion of the manual?

According to the APYP bin (dowloadable from TunerPro), the factory settings for the MAIN fan are 225 (on) and 220 (off). Because the ECM picks up it's temp readings from the CTS vs the DASH sensor, people might assume turn-on temps are higher.

As I mentioned in another thread, the DASH temp is higher than the CTS reading....by about 10-deg.

 

Yes I see on the schematic section page 8A-31-1 shows the auxillary cooling fan temp. switch closes at 228*F. That is incorrect and a misprint, the switchs are rated to close at 238*F The main engine fan which is controlled by the ECM is stated to close at 226*F according to my FSM.