Radiator Fans only working with A/C on

[MrsMcNastys]

Hi Guys,

You guys have been a great help on maintaining 2 low mile ZR-1's with fixing the secondaries, injectors, thermostat etc.

Need some help on this one - 1990 ZR-1, 15,000 mile original car in the shop with customer complaint of overheating at idle/traffic.

Thermostat appears to be working correctly, with A/C off reached operating temp and no fans activate, temp hovered at mid gauge range at idle then slowly crept up higher.

Turn on A/C - both fans kick on, quickly brings temp down below half way, cycles on and off - can idle for hours no problem.

Turn A/C off - no fans, let the temp climb quite a bit one time to see if fan activation was delayed - still nothing.

Have verified both fans operating with A/C, relays good etc.

I am thinking ECM temp sensor? But, this same sensor is telling the fans to cycle on/off with A/C on also?

Found the ECM pins here:

http://www.zr1.net/forum/showthread.php?t=12004&page=2

Identified:

C2 A/C Request

C6 Primary Fan

C8 Fan Request

D11 Secondary Fan

So C6 and D11 would be the ECM grounds to activate relays?

C8 would be to the ECM temp Sensor, does the A/C request just activate the ECM grounds based on compressor pressure? It would seem to use the temp sensor to cycle.

In any case I cannot identify the other pin for the ECM temp sensor as it is a two-prong item. Once identified can I ohm it out before I pull the plenum?

We are a old-school speed shop and primarily work on pre-72 muscle cars. The same customer has a 375 HP 69 Nova SS he bought new and he was so happy with our work on that he brings us everything now.

Any suggestions would be greatly appreciated.

Ed

[Franke]

The primary fan turns on when:
AC request signal indicated yes, or Engine speed has been < 3500 rpm for 12 secs and Engine oil temp > 226 degree F, or Engine speed has been > 3500 rpm for 12 secs and engine oil temp is > 217 degrees F, or AC request indicated yes and vehicle speed < 12 mph and coolant temp > 226 degrees or AC request not indicated and vehicle speed >12 mph and coolant temp > 234 Degrees. So it would appear to me that the request for fans on AC are independent of the CTS or can be a combination of vehicle speed, oil temp, coolant temp and AC request. The secondary fan will not turn on if the primary doesn't run for at least 2 seconds. I would check the Coolant temp sensor first. Do you have a scan tool?

[c4koh]

The primary fan turns on when:
AC request signal indicated yes, or Engine speed has been < 3500 rpm for 12 secs and Engine oil temp > 226 degree F, or Engine speed has been > 3500 rpm for 12 secs and engine oil temp is > 217 degrees F, or AC request indicated yes and vehicle speed < 12 mph and coolant temp > 226 degrees or AC request not indicated and vehicle speed >12 mph and coolant temp > 234 Degrees. So it would appear to me that the request for fans on AC are independent of the CTS or can be a combination of vehicle speed, oil temp, coolant temp and AC request. The secondary fan will not turn on if the primary doesn't run for at least 2 seconds. I would check the Coolant temp sensor first. Do you have a scan tool?

Interesting to read that.
I had a situation a few days ago where the engine was hot (very hot) and both the analog gauge and the digital gauge read hot (260), albeit for only a few minutes. Neither primary nor secondary fan would come on when I was stopped. Car was at idle.

In the various scenarios above, I didn't see what would happen if coolant temp > 234, AC request off, vehicle speed <12 mph (in my case, stopped). Is it only if oil temp >226F will the fans go on at vehicle stopped and AC is off?

In any case, what I did learn is that in case I see this again, switching the AC on will put the fans on if coolant is hot, and car is slow (<12 mph).

Learning all the time :)

Steve

[Franke]

I would check the CTS for proper resistance since it is a thermistor. It could go out of calibration. Interestingly the chart in the FSM indicates the max temp for the CTS at 212 degrees F and the low temp at -40 degrees F. Resistance at 212 degrees is 177 ohms.

[XfireZ51]

If the fans are coming on w A/C request then it's probably not the relays or the ECM. It's why maintaining good grounds is important to proper engine controls. ECM turns things on and off by grounding circuits.

[Jim Nolan]

I'll add on to the importance of the grounds. When I went to Gordon's school many years ago he placed a heavy emphasis on grounds by grinding them into the frame and not repacing the star washer with flat ones.

Jim

[MrsMcNastys]

We have an Actron CP9145 with an OBDII connector. Would that support with the correct connector?

Ditto on the grounding, we redundantly ground all builds especially our LS1 swaps.

Does the FSM list a procedure for checking the CTS? We only have the supplement.

Ed

[LGAFF]

First statement in FSM ....if the engine is actually overheating and the gage indicates overheating, but the cooling fan is not coming on the coolant temp sensor has fell out of calibration and should be replaced.

[LGAFF]

http://i134.photobucket.com/albums/q115/lgaff/DSCN5871.jpg (http://s134.photobucket.com/user/lgaff/media/DSCN5871.jpg.html)

http://i134.photobucket.com/albums/q115/lgaff/DSCN5870.jpg (http://s134.photobucket.com/user/lgaff/media/DSCN5870.jpg.html)

http://i134.photobucket.com/albums/q115/lgaff/DSCN5873.jpg (http://s134.photobucket.com/user/lgaff/media/DSCN5873.jpg.html)

http://i134.photobucket.com/albums/q115/lgaff/DSCN5872.jpg (http://s134.photobucket.com/user/lgaff/media/DSCN5872.jpg.html)

[MrsMcNastys]

Thanks LGAFF,

Ordered the necessities from Jerry on Sunday and they arrived today so we are pulling the plenum!

Ed

[MrsMcNastys]

OK so we have done the ECM coolant sensor swap with no change in problem.

Went back and verified fans, relays wiring again everything as it should be.

Fans only activate with A/C operating or pressure switch connector unplugged.

Was able to figure out engine data from A/C system control screen to verify ECM knows engine temp to activate and it does know correct engine temps.

Soooo ... we are back to square 1. Having a second ZR-1 available is a great resource as we will be swapping chips and ECU to determine if that is the problem.

Special thanks to Marc Haibeck who took the time to help on the phone, this one is a head scratcher for him also.

Ed

[c4koh]

Interesting to read. Since my analog gauge and my digital gauge do seem to both be working, and my fans weren't turning on, I also suspect that even if I did swap the Coolant Temp Sensor, then I'd still have had the issue.

If the digital guage reads 235, then I'd like to presume that the ECM thinks it's 235 too... and if so, if it's not switching on the fan, then there must be some other reason...

Of the replies so far, my hunch would be with a loss of grounding. In other words, assuming that the 235 reads true, the ECM flags 'ON', perhaps something between there and the fans isn't tripping... whereas the AC switch does trip to switch it on...

I wonder if it's feasible to test the ECM 'ON' (without a Tech 1, isn't there a way to ask it to test it too??) to see if that's the issue? (lack of good ground)???

Steve

[Franke]

The grounds are important for the ECM to command the cooling fan relays. I would also verify the wiring from the CTS back to the ecm just to make sure its not bad. You should also be able to read the CTS resistance at the ecm plug looking back to the CTS to help verify continuity.

[MrsMcNastys]

Thanks guys,

Haibeck confirmed what we already figured - that the relays, wiring, fans etc all work off the same circuit from the ECM from E6 and D11 wether they are activated by the engine temp or the A/C request.

Seems like all that can be eliminated as the problem. The fans ground fine and work great under A/C request, the computer "grounds" E6 and D11 to activate the relays under A/C request. Disconnecting the A/C request switch immediately activated the fans.

ECM knows coolant tempurature as demonstrated on the A/C parameters check so CTS (new from Jerry's) has not "shifted out of calibration" as stated in FSM.

We might have a bad cooling chip or the ECM may also be going - but that is really down to less than 1% probability.

Ed

[XfireZ51]

'How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?'

Sherlock Holmes Quote

I'll look at the chip if you want.

[LGAFF]

Gordon Kilibrew?

[c4koh]

Thanks guys,

Haibeck confirmed what we already figured - that the relays, wiring, fans etc all work off the same circuit from the ECM from E6 and D11 wether they are activated by the engine temp or the A/C request.

Seems like all that can be eliminated as the problem. The fans ground fine and work great under A/C request, the computer "grounds" E6 and D11 to activate the relays under A/C request. Disconnecting the A/C request switch immediately activated the fans.

ECM knows coolant tempurature as demonstrated on the A/C parameters check so CTS (new from Jerry's) has not "shifted out of calibration" as stated in FSM.

We might have a bad cooling chip or the ECM may also be going - but that is really down to less than 1% probability.

Ed

I'm not so sure this reasoning is 100%. As the diagram shown in the FSM (and posted by LGAFF), the ECM controls the fans to be on with the AC request from the pin C8, and in this case everything appears to be working. C8 does make ground according to that diagram.

The ECM would seem to therefore be working: its programming logic working in so far as switching AC on triggers the pin C8. I would doubt that the logic is only working in some places... and the ECM surely needs to be working for the other two fan relay pins (C6 and D11), otherwise likely it wouldn't work at all. So my opinion would not be a bad ECM, though of course it's not impossible.

My hunch does remain that of grounds: perhaps there is a good ground created when the AC is switched on [being the ground from the AC switch on circuit 450 Black]... and this works, clearly. This being said, I can't see (though will look more later) how that circuit affects the fan relays... but still.

But perhaps when the control to the cooling fans is only via the ECM (i.e. absent the control of the AC] then here there are insufficient grounds, and therefore lack of power to the fans.

The ground to check would seem to be the circuit 151 Black in any case...

Does that sound plausible??

Steve

[WVZR-1]

I would think you could maybe pin down the problem by just grounding the primary fan relay. If the fan runs then it would indicate there's a problem internally either to the PROM or the ECM. It's nice to have the luxury of the second ECM/PROM but how similar are the PROMS? Same source? Who knows. I think the grounding of the primary relay to start the fan would be certainly the easiest diagnostics to start with. Just thinkin'

I don't see anywhere it's mentioned that it's been confirmed. I only see the operation confirmed by the AC. Maybe I've overlooked something here.

[XfireZ51]

After re-reading this,by any chance did you ground the A/B terminals(as for reading codes) of the ALDL port and then turn ignition "ON"? Fans will come on then and that would be going thru the ECM and grounds.

[Franke]

OK so we have done the ECM coolant sensor swap with no change in problem.

Went back and verified fans, relays wiring again everything as it should be.

Fans only activate with A/C operating or pressure switch connector unplugged.

Was able to figure out engine data from A/C system control screen to verify ECM knows engine temp to activate and it does know correct engine temps.

Soooo ... we are back to square 1. Having a second ZR-1 available is a great resource as we will be swapping chips and ECU to determine if that is the problem.

Special thanks to Marc Haibeck who took the time to help on the phone, this one is a head scratcher for him also.

Ed

Is there really a problem here? Based on what I read in the FSM, it looks like the primary fan should come on at 234 degrees F + if AC is off. Engine oil temp also factors into the fan request as well so if the temps are not as high as the FSM indicates there would be no fans request from ECM.
You indicate the you were able to figure out engine data from A/C system control screen to verify ECM knows engine temp to activate and it does know correct engine temps. Just curious if it met these FSM parameters?

[Dynomite]

Is there really a problem here? Based on what I read in the FSM, it looks like the primary fan should come on at 234 degrees F + if AC is off. Engine oil temp also factors into the fan request as well so if the temps are not as high as the FSM indicates there would be no fans request from ECM.
You indicate the you were able to figure out engine data from A/C system control screen to verify ECM knows engine temp to activate and it does know correct engine temps. Just curious if it met these FSM parameters?

Good question :cheers:

Hi Guys,
Thermostat appears to be working correctly, with A/C off reached operating temp and no fans activate, temp hovered at mid gauge range at idle then slowly crept up higher.
Turn on A/C - both fans kick on, quickly brings temp down below half way, cycles on and off - can idle for hours no problem.
Turn A/C off - no fans, let the temp climb quite a bit one time to see if fan activation was delayed - still nothing.
Any suggestions would be greatly appreciated.
Ed

It is not known from the description exactly what the coolant temperature was in degrees F during the testing.

As an aside......... Marc Haibeck's Calibration AYBKG (1990) (http://www.zr1specialist.com/HAT%20Web/products/Calibration%20AYBKG.htm) Turns both of the cooling fans on at 205 degrees F. Both turn off at 200 degrees F.

[XfireZ51]

I 'm looking at a stock 90 bin file AYBK, and it shows Fan 1 ON at 112C which sounds awful high for me. Fan 2 ON at 114C.

A stock 92 calibration w fans (see attached)

107C/112 under 12mph

112/114 over 12mph

If the cal is stock, you may be waiting a while for fans to turn on. The gauge at the middle is 100C and its non-linear

[WVZR-1]

A stock 92 calibration w fans (see attached)

107C/112 under 12mph

112/114 over 12mph

If the cal is stock, you may be waiting a while for fans to turn on. The gauge at the middle is 100C and its non-linear


See if you have any information on the '92 PROM BATL (16175910) - just acknowledge I'd like the thread to continue with the OP's problem but since you mentioned '92 I thought I'd ask.

[Dynomite]

I 'm looking at a stock 90 bin file AYBK, and it shows Fan 1 ON at 112C which sounds awful high for me. Fan 2 ON at 114C.



That IS high at 234 degrees F.....that is why a lot of us install Marc Haibeck's Calibration AYBKG (1990) (http://www.zr1specialist.com/HAT%20Web/products/Calibration%20AYBKG.htm") Turns both of the cooling fans on at 205 degrees F. Both turn off at 200 degrees F.

I am thinking (and analog gauges are estimates) that 234 deg F is way up close to the cross hatch area.

The trouble of using the AC Fans ON to cool down the engine is simply that with AC on (unless you set the interior temperature low) the AC condenser increases the heat through the radiator (additional HOT air through the radiator raising coolant temperatures).

[XfireZ51]

See if you have any information on the '92 PROM BATL (16175910) - just acknowledge I'd like the thread to continue with the OP's problem but since you mentioned '92 I thought I'd ask.

I know that the 2 broadcast codes for 92 were AZZC and BPPA. Had not heard of a BATL.

[XfireZ51]

OK. Actually 3 bins for 92 AYWT, AZZC, and BPPA. All w the same values as the stock 92 bin I previously posted. 107/112, 112/114C

[WVZR-1]

I know that the 2 broadcast codes for 92 were AZZC and BPPA. Had not heard of a BATL.

BATL was a '92 only EXPORT PROM. I've got a few NOS and I was just curious. Thanks!

[XfireZ51]

BATL was a '92 only EXPORT PROM. I've got a few NOS and I was just curious. Thanks!

Ah! If you want to send it over I can do a compare.

[Franke]

Interesting info XfireZ51. 112Centi is 233 degrees farenheit and 114Centi is 237. I'm trying to understand why so high before fan request without AC. Is it possible maybe these bin values are modified somewhere else by other ECM inputs to lower the fan turn on request?

I have Marcs chip in my ECM and did see that the fans acted just as Dynomite says.

[WVZR-1]

So ideally if you had access to the CTS you would ground the primary fan relay to confirm operation and then supply the ECM with values from the CTS connector to match the Delphi published specifications.

Fan runs w/relay grounded (fan is OK), fan doesn't run when supplied the required resistance the assumed problem is internal to the ECM?

Here's Delphi specs for the GM 12146312 CTS:

http://www.pe-ltd.com/joomla/images/downloads/coolant_temp.pdf

[XfireZ51]

So take the pin for the ECM ground to the fans and ground it. See if the fans turn on. Basically, grounding the A/B ALDL pins will tell you the same thing.

[XfireZ51]

Interesting info XfireZ51. 112Centi is 233 degrees farenheit and 114Centi is 237. I'm trying to understand why so high before fan request without AC. Is it possible maybe these bin values are modified somewhere else by other ECM inputs to lower the fan turn on request?

I have Marcs chip in my ECM and did see that the fans acted just as Dynomite says.

No. Likely this was done to keep exhaust hot for cats. I just installed a Fluidyne rad. If I don't raise the fan request temps, CTS drops below temp where ECM LEARNS for updating BLMs.

[WVZR-1]

So take the pin for the ECM ground to the fans and ground it. See if the fans turn on. Basically, grounding the A/B ALDL pins will tell you the same thing.

No I believe you would ground the relay directly to confirm fan operation, return everything to correct wired scheme and then supply required resistance to the CTS connector to confirm that the ECM ground is being switched when the correct resistance is being seen by the ECM.