mean8t

I have finally fixed the cooling fans on the Vette. The relay wasn't getting power from the ignition, now that the fans work, they run all the time that the engine is running.

What would make them run all the time?

Thanks for your help.

scorp508

Is your SES light on?

Is your fan switch wire shorted to ground somewhere?

mean8t

I will check the fan switch wire today, I don't have a SES light yet, I am in the process of installing an ALDL and SES light in my 80 vette.

skateparkdave

Does your AC work??? The fans are activated by the high pressure switch and will run while AC is on or when an AC has been disabled and doesn't work, but the switch and wire are left intact. Often the high pressure switch just needs to be unplugged from high side line if AC doesn't work or is disabled.

Wait, are we talking about a C3 here??? Could be different...not sure. Try posting in C3 tech..

65Z01

Since you are tunning TPI on your '80 I assume you have an ECM from a TPI car.

In which case the commentary about the A/C pressure switch is quite valid. Check to see that the line into your ECM is grounded as the ECM wants to see a ground signal there.

Also check the coolant temp sensor under the front of the TB in the intake base. It should read in the 100k Ohm range when cold and in the 1k Ohm range when hot. So if the ECM is seeing a low resistance on that line it will bring the fans on.

The other possibility is a short on the command line into the fan relays.

mean8t

No the AC doesn't work. Will it in a few weeks when I recharge it, yes. Where does the high pressure switch go exactly???? Can one of you guys post a picture??? I am assuming that I will need one when I get that system up and running.

SunCr

For a TPI, there are two switches on the a/c high pressure line. One is the high pressure switch which will open the clutch circuit if the high side exceeds 425psi. The other is a fan switch which is wired to the ECM. Normally closed, it opens at 230 psi which signals the ECM to ground the main fan relay. It will close again when the pressure drops to about 170 psi, and the ECM then turns off the fan (assuming the engine temp is below 226 degrees). Below 80 degrees, the fan will cycle on and off, at idle, as the pressure rises and then falls with the cooler air across the condensor. Above 80, the high side generally doesn't get low enough for the switch contacts to close, so the fan will stay on. In any event, if you're using a TPI ECM to control your fan relay, then you need a ground at Pin D11 (a/c fan switch signal). With that, the ECM will only ground the fan relay when the Engine Coolant Temp Switch indicates 226 degrees. Absent a/c, that's how it was designed. With a/c, you'll want the switch or some other means to make sure the fan comes on at idle. The condensor has to be cooler than the radiator for good vent temps. I believe there are kits available that place a thermostat like device on the condensor which you could probably wire directly to the relay or you could use the switch. Given that your setup is a C3, you'll probably need to fabricate custom lines. You will also need a wire from the a/c clutch circuit to ECM Pin B8. That will signal the ECM to increase IAC counts for the load of the compressor. Without the signal, it isn't going to idle or the idle will surge. Unfortunately, that might be a bit tricky as with the manual air option, the signal is 12 volts - for electronic air, the signal is 5 volts. I believe that either option uses the same ECM with the difference burned into the PROM, but you might want to to check with your supplier and make sure you've got the right ECM or Chip.

skateparkdave

Again, mine is a 1990 but here's some pics of me pointing to the high pressure fan switch. It's the smaller oval switch on smaller high pressure line down low. It's kind of hard to get a good pic of but I tried.
Hope it's helpful.

runner140*

If you run your A/C, that will trigger your fans on. Try turning off your A/C and see it the fans go off.

AGENT 86

Maybe your wiring is incorrect. Hereis some info you find usefull
http://members.shaw.ca/corvette86/Co...%20Control.pdf

mean8t

Thanks for all your help guys.

One more thing does anyone have a wiring diagram that has all the pinouts for the ecm??

SunCr

Depends on the TPI setup you're using. A/C cooling fan operation is different for the '90 - '91 then the one I described. It uses 3 wire single pressure switch that receives a 5 volt reference from the ECM. The return voltage indicates system pressure (each volt is about 100 psi) and this signal is used to ground the main and aux fan relays. It is also used to shutdown the a/c system if the pressure is too high or too low (it will set a trouble code if it is too low). Unlike the '85 - '89 setup, an open on this circuit would not turn on the fans - the ECM ignores the signal unless an a/c request is sent on another circuit. You might want to talk to the guys at Street & Performance, www.hotrodlane.cc - they do a lot of TPI conversions.

mean8t

It is an 85 setup.

I will email the guys at S&P

65Z01

For an '85 ECM;
-The A/C pressure sensor feeds into pin C9.
-Coolant temp sensor in on C10.
-Fan relay is out on D2.

Robbie964

my cooling fans are running when the engine is turned off and it drained my battery. Replaced all cooling fan relays and it is still doing it. Any suggestions