Both fans would run continuosly from time I turned key on.

-Sender in pass side head is new
-CTS is new
-Hypertech 160 fan switch and chip new
-I might add fans ran continuosly with the stock chip/fan switch also.

Replaced both relays (one on inner D.S. fender, other on fan shroud)
Autozone, GP Sorensen #MR44 fwiw, $10 ea.

Turned key to "on", coolant temp 168 on dash, aux. fan is on.
Turned on and let it idle for a bit, at approx 180 the main fan came on.

Is this corect?
I thought the main fan comes on early and the aux. later. ???

Noticed one of the terminals in the harness for (Main fan?) on D.S. fenderwell looked a little dark, anything to worry about, Im assuming its due to a bad relay?

BTW, Autozone sells seafoam, shes soaking in it right now. Smoke show to come soon ....

 

NO. However it is impossible to know the correct on and off temps.
That IS correct. But again, it is impossible to know the correct on and off temps with your non-stock parts.

You said that the fans came on immediately and simultaneously, both before and after the parts changes. I suspect some wiring problems that preexisted your changes remain. What are your A/C controls set to through all this testing?

RACE ON!!!

 

AC controls are off.

After I changed the relays and restarted the car the main fan was off, the aux. was running. At about 180 the main came on.
Ill let the car cool off completely and start from scratch..Ill post when the fans come on and at what temp, probably in the AM, gotta get the oil changed in a bit. .I dont mind if they come on at 160 and 180, just as long as they dont run 100% from startup.

The fact that the aux. comes on before the main confuses me.

 

Ya bumped the manual fan switch!

 

Manual fan switch is off, Im going to unplug the AC pressure switch and see what happens, wonder if its no good

 

They are 100% independent of one another. Your aux fan switch MAY be for a cooler temp than the prom has programmed for the main fan. My '84 has one fan and it operates off of a switch, like your aux fan. It is set to come on at 205° (now) but it never runs unless I get stuck in traffic.

RACE ON!!!

 

If both fans are running, someone has tied the grounds together. OEM is 226 for the main; 228 for the aux unless the a/c is on - then 230 psi (about 135 degrees) on the high side will ground the main fan relay until it drops to 170 psi (about 115 degrees). Doubt a custom burn did anything to change the a/c signal - but who knows? It may well have changed the threshold for main fan operation absent the a/c signal, but it should still be at a higher temp than what the a/c needs to operate correctly.

I would verify the temp sensor input. The last time my ECM went bad, it was toggling between 228 and 250 even when cold. The main fan was on at startup and there was no fast idle, so that gave me some clues about where to look. If you don't have a scanner, you can throw 9 bucks at another sensor and compare how many ohms it has across it's terminals with the one installed on your Vette after it's sat overnight. They should be close. You can also just plug it in to the harness and see if anything changes when you start it up. Otherwise you can check the pinout from ECM C10. It's a 5 volt reference and with the sensor unplugged, you should see the 5 volts. With it plugged in and on a cold engine (really depends on ambient), it will be somewhat less, but on a hot engine, a really big difference (resistance decreases as it warms up so the voltage drop is greater).

The a/c fan switch is normally closed and opens when the pressure gets to about 230psi. The ECM then senses the voltage and drives or grounds the main fan relay. Once the pressure drops to about 170, the switch closes, the voltage at the ECM drops to 0 and ground is removed from the main relay. SO, if you disconnect it, the fan will (should) come on and stay on. Easy to troubleshoot with a scanner, but if you suspect the switch, put your DVM across it's terminals with the engine cold. It should read closed. Then read the voltage and verify the circuit at the ECM, Pin D11. With the key on and everything hooked up, should be 0. Then with a/c running and when the pressure hits 230, voltage should rise to battery, drop back to 0 when it hits
170. Whatever you get should point you in the right direction - open ground or signal wire, faulty switch or faulty ECM - assuming of course this circuit is the problem.

 

PS - you won't pass emissions at the temps you're running or if you do, let the OEM's know - you'll be a rich man.

 

Yeah, Ill need to disconnect the aux. fan and get it warm. Ran some seafoam through it a little while ago, hardly any smoke, figurd it was clean. Reset the timing, install a new IAC (old one jumps a bit)and hold my breath .
FWIW, the test only centers use those giant fans directly in front of the car to "blow fumes out of the station" and have a tendency to cool the car off a little too much

 

Disconnected the AC press switch by suitcase after it cooled down (133 deg.) with key "on", no fan, or with it connected either. Guess that ones Ok

 

As CFI said your fans are independent of each other. It looks like they are coming on at different times.

Unplug the sensor on the DRIVERS head to see if your AUX fan shuts down. You may have a low temp sensor in that hole.

What chip is in that car? If it is a chip with a low temp setting it will make your MAIN fan will come on early.

 

with everyone.
Ditch the hypertech fan switch. Thats more for someone that has a stock chip and is looking to tie the lower temp fan switch into the main fan relay.
I picked up a 200* fan switch for my aux fan and will have my new chip programmed to match my 170* stat.
I crossed some numbers i found here and got a Niehoff TS25691 fan switch. I believed i crossed a nappa number to get this one local.

 

you didn't tell me about that
Checking as suggested by sun cr is a good idea.

I know you said it did the same with the stock parts. I still think it would be good to eliminate the aftermarket parts (switch and chip)to be able to find or eliminate that as the possible source of the problem (since no scanner, who knows where those are programmed to kick fans on).

 

It does sound like someone has replaced the aux. fan temp switch, the one in the drivers side head with a lower temp switch. When I wanted the fans to come on earlier I replaced the temp switch there and wired it so both fans come on earlier-at the same time, of course if I sold it I'd have to let the buyer know-or They'd always wonder WTH.

 

The fan should be on when it's disconnected - sounds like you unplugged the high pressure switch or low pressure switch at the evaporator housing. You want the one on the smaller line from the condensor to the Evaporator next to the high pressure switch. Harness is dk green black and the high pressure switch is light green black.

 

Or save the nine bucks and look in your FSM. The Ohms are listed for different temperatures, in my Helms.


"With it plugged in and on a cold engine (really depends on ambient), it will be somewhat less" No. It will be a lot less. "but on a hot engine, a really big difference" A much smaller difference. "resistance decreases as it warms up" Is correct, but "so the voltage drop is greater" is wrong. As the resistance DECREASES, the voltage rises, it doesn't drop.

RACE ON!!!

 

You're right! More coffee! More Coffee!

 

I've had my coffee now. At the ECM side it drops. At the ground it will rise. Try it and see or better yet, review the Code 14 and 15 Charts: "As the engine coolant warms, the sensor resistance becomes less, and the voltage drops." The reference is to what the ECM is seeing.

 

My trouble shooting chart says:
"Engine at normal operating temperature.
Disconnect coolant sensor.
Ignition "on", engine stopped.
Check voltage between harness connector terminals. CKT 410 and 452.

Over 4 volts:

Check Resistance across coolant sensor terminals. Should be over 100 Ohms."

To me, that means that hot (operating temperature) the voltage is high 4 volts vs 5) while the hot sensor ohms are low (210° water = 185 Ohms).

What do you mean by "At the ECM side it drops"? Circuit 452 is grounded inside of the ECM.

RACE ON!!!

 

FSM's have charts for the range of the Thermistors used by GM. ECM reference is 5 volts. Starting at the ECM Pin and with the sensor disconnected you will (should) see this voltage. Hook it up and check again (at the pin). Depending on the resistance in the sensor, that voltage will drop. Higher the temp - lower the resistance - higher the drop. I like to start at the ECM to verify the reference with the harness disconnected and then make the same measurement with it all hooked up. If everything thing checks out there, you know that the wiring and sensor are good leaving the possibility that the ECM is bad (and a scanner is the best way to see that). You can measure both sides at the sensor too. Disconnected, you will only verify the reference. Otherwise, you'll need to backprobe the harness or pierce the insulation or find the ground splice which is shared with the MAT and TPS (on allmost all GM's through at least '95) and travels back to Pin D2 at the ECM - I'd hate to try any of that to say nothing of the extra resistance you might put in the wiring by sticking a hole in it. Yes, it's a pain to lay on your back and then hope your probe is touching the correct pin - but it's the best way as far I'm concerned - unforturnately, Cuisinart just blew a head gasket so he'll be taking quite a bit more apart.