Cooling fan relays
05-12-2012, 11:22 PM
#1
Instructor
Thread Starter
Cooling fan relays
Aloha gang,
Noticed my fans arent coming on when the car is cold and i turn the ac on. I changed the 2 relays that are interchangable, i think it was 43 and 44, the 4 pin relays, still the same problem. Is it the 5 pin relay that controls the ac on fans? All fuses are good as the fans do come on when the car reaches temp, for me its on at 186* and off at 175*. Custom tune.
Noticed my fans arent coming on when the car is cold and i turn the ac on. I changed the 2 relays that are interchangable, i think it was 43 and 44, the 4 pin relays, still the same problem. Is it the 5 pin relay that controls the ac on fans? All fuses are good as the fans do come on when the car reaches temp, for me its on at 186* and off at 175*. Custom tune.
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Willard Beard (05-25-2016)
05-13-2012, 01:06 AM
#2
Team Owner
Aloha gang,
Noticed my fans arent coming on when the car is cold and i turn the ac on. I changed the 2 relays that are interchangable, i think it was 43 and 44, the 4 pin relays, still the same problem. Is it the 5 pin relay that controls the ac on fans? All fuses are good as the fans do come on when the car reaches temp, for me its on at 186* and off at 175*. Custom tune.
Noticed my fans arent coming on when the car is cold and i turn the ac on. I changed the 2 relays that are interchangable, i think it was 43 and 44, the 4 pin relays, still the same problem. Is it the 5 pin relay that controls the ac on fans? All fuses are good as the fans do come on when the car reaches temp, for me its on at 186* and off at 175*. Custom tune.
It sounds like your relays are working properly due tothe fact that they do come on when at temp -
Do a few more test - you might need to look at the Helms Manual schematic to see how the AC triggers the fans and which relay that one is -
Thanks,Matt
05-24-2016, 10:25 PM
#3
Heel & Toe
I have a similar problem but different. Both of my fans run at high speed with the AC on but neither run with the AC off. I have removed the fans and they both will run on the bench in high and low speed. i replaced all 3 relays. i ran the engine and let it get up to 205 degrees and neither fan came on in either high or low speeds. I even checked the wires from the fans to the fuses with an ohm meter and they all have continuity. I am at a loss for what is causing this problem. Your suggestions and recommendations will be greatly appreciated.
What sensor triggers the cooling fans to come on? Where is it located? Should I change it next? My temperature gauge works normally (both the analog gauge and the digital gauge in the DIC)
What sensor triggers the cooling fans to come on? Where is it located? Should I change it next? My temperature gauge works normally (both the analog gauge and the digital gauge in the DIC)
05-24-2016, 11:47 PM
#4
Pro
I have a similar problem but different. Both of my fans run at high speed with the AC on but neither run with the AC off. I have removed the fans and they both will run on the bench in high and low speed. i replaced all 3 relays. i ran the engine and let it get up to 205 degrees and neither fan came on in either high or low speeds. I even checked the wires from the fans to the fuses with an ohm meter and they all have continuity. I am at a loss for what is causing this problem. Your suggestions and recommendations will be greatly appreciated.
What sensor triggers the cooling fans to come on? Where is it located? Should I change it next? My temperature gauge works normally (both the analog gauge and the digital gauge in the DIC)
What sensor triggers the cooling fans to come on? Where is it located? Should I change it next? My temperature gauge works normally (both the analog gauge and the digital gauge in the DIC)
Factory settings to turn on the cooling fans is ON at 226 degrees in low speed mode (both fans run but are electrically configured in series so that each fan has about 1/2 of battery volts across each motor so at slower than rated speed). Fans go off at 219 degrees or once the vehicle speed exceeds 35mph. If the coolant temp kept going up the fans go into high speed mode at 235 degrees. In high speed mode the electrical configuratio is changed from series to parallel. In parallel mode both fans have the full battery voltage across each fan motor so they run at full rated speed. They revert to low speed mode once the coolant temp reaches 226 degrees..
If you want the fans to come on sooner, turn on the AC and the low speed operation begins at coolant temp of about 185 degrees. High speed operation with AC on remains at 235 degrees.
05-25-2016, 08:32 AM
#5
Heel & Toe
The PCM is what actually turns the fans on/off and it does so based on input from the engine temp sensor (drivers side head just behind the alternator) and then compares it to the turn on/off values stored in the PCM. With a tuning tool the on/off values in the PCM can be set to something other than the factory values.
As the previous post spells out the factory settings for those values are relatively high and apparently your car is not reaching the set values hence the fans are not coming on other than when the AC is running and the ON point for that condition is exceeded.
As the previous post spells out the factory settings for those values are relatively high and apparently your car is not reaching the set values hence the fans are not coming on other than when the AC is running and the ON point for that condition is exceeded.
Thanks for the information. I have two more questions. Where is the PCM located and what type of tuning tool is required to reset the on / off values? I guess I have a third question, where can I get the needed tuning tool.
I am grateful for any and all information. Thanks
05-25-2016, 08:48 AM
#6
Pro
Thanks for the information. I have two more questions. Where is the PCM located and what type of tuning tool is required to reset the on / off values? I guess I have a third question, where can I get the needed tuning tool.
I am grateful for any and all information. Thanks
I am grateful for any and all information. Thanks
05-25-2016, 08:53 AM
#7
Heel & Toe
I will do that this morning. I usually don't like my car to run that hot but I need to know that my cooling system is working as it should. Any information you can offer on the "Tuning Tool' would be appreciated. Thanks
05-25-2016, 10:43 PM
#8
Heel & Toe
First I agree with the advise of Ducati Guy........ 
The PCM is located under the battery. You need to remove the battery and the battery shelf to see it. No need to physically get to the PCM unless your car has had the battery leak acid and damage the items below the battery. The PCM is programmed through the OBDII port.
I have heard that there are some hand held programming tools that can reset the turn on/off temps but I do not know the brand names that can do that. The ones I have heard about cost $300 and up.
There are programming software tha run on a PC that can do that as well as change other parameters in the PCM. Two well known ones are HP Tuners and EFI Live. Both are pretty expensive and require more than a little knowledge to use. Many tuners will charge you around $100 to change parameters like the fan turn on temps, CAGS elimination if you have a manual trans, reset column lock fuel shutoff speed, etc. That cost is largely due to the cost of the software license since they are licensed per VIN. Their time to do simple things is small. Before I had my car tuned (had a Maggie installed) I did have the CAGS eliminated, fuel shutoff speed set high and the fan turn on temps changed lower and the tuner spent less than 5 minutes and charged $100. I think it took more time for his laptop to boot up than the actual changes.
The PCM is located under the battery. You need to remove the battery and the battery shelf to see it. No need to physically get to the PCM unless your car has had the battery leak acid and damage the items below the battery. The PCM is programmed through the OBDII port.
I have heard that there are some hand held programming tools that can reset the turn on/off temps but I do not know the brand names that can do that. The ones I have heard about cost $300 and up.
There are programming software tha run on a PC that can do that as well as change other parameters in the PCM. Two well known ones are HP Tuners and EFI Live. Both are pretty expensive and require more than a little knowledge to use. Many tuners will charge you around $100 to change parameters like the fan turn on temps, CAGS elimination if you have a manual trans, reset column lock fuel shutoff speed, etc. That cost is largely due to the cost of the software license since they are licensed per VIN. Their time to do simple things is small. Before I had my car tuned (had a Maggie installed) I did have the CAGS eliminated, fuel shutoff speed set high and the fan turn on temps changed lower and the tuner spent less than 5 minutes and charged $100. I think it took more time for his laptop to boot up than the actual changes.
Well I finally had time to check out the fan operation. The information provided was most helpful. I didn't know the fan on / off setting was so high. I ran the engine and let it reach 226 degrees and both fans came on in low speed and stayed on until the temp dropped to 217 degrees. I let it cycle several times and it was consistent. I then turned on the AC and the fans came on in high speed and brought the temp down to 195 degrees. They stayed on while the AC was on.
It seems that the fan relay #44 was not working properly which was causing my problem plus my lack of understanding of the on / off limits. I replaced relay #44 and that seems to have corrected the problem.
Now, I need to find someone that can reprogram the cooling fan On / Off limits. I don't like to run my engine much above 200 degrees.
Thanks for all of your ideal and information which helped me understand and solve this problem. Now, on to the next problem the dreaded ABS Active Handling warning on the DIC.
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c5007Alvarado (10-02-2023)
05-26-2016, 04:44 PM
#10
Heel & Toe
try this link http://www.rangeracceleration.com/C5_Fan_Trick.html also saw a variation with a switch put inline
Thanks for the information on the C5 fan trick. That might come in very handy. Now, I need to get the codes to see what I need to look at with the ABS AH. There aren't enough hours in the day for MY stuff.
05-26-2016, 04:58 PM
#12
Heel & Toe
I think what I will do is split the wire and add a toggle switch and mount it next to the fuse / relay box. That way, all I have to do is raise the hood and flick my switch. Thanks, that was a great and easy and useful trick.
05-26-2016, 09:55 PM
#14
Pro
before messing with the fans on / off settings which will have an effect on the engimes operating temps I would carefully read the info posted by Evil Twin. I go with what ever he says. And he says these engines are designed to run on the warm side of things.
Always remember that unless something is not working as designed.............millions of dollars were spent by very smart engineers in the R&D of every aspect of these cars. I choose to defer to that gang and let the car be as they deemed best. Now of course if you think you know more or better than them.....have at it. Make some changes.
Always remember that unless something is not working as designed.............millions of dollars were spent by very smart engineers in the R&D of every aspect of these cars. I choose to defer to that gang and let the car be as they deemed best. Now of course if you think you know more or better than them.....have at it. Make some changes.
06-16-2018, 09:39 PM
#15
This should help::
Factory settings to turn on the cooling fans is ON at 226 degrees in low speed mode (both fans run but are electrically configured in series so that each fan has about 1/2 of battery volts across each motor so at slower than rated speed). Fans go off at 219 degrees or once the vehicle speed exceeds 35mph. If the coolant temp kept going up the fans go into high speed mode at 235 degrees. In high speed mode the electrical configuratio is changed from series to parallel. In parallel mode both fans have the full battery voltage across each fan motor so they run at full rated speed. They revert to low speed mode once the coolant temp reaches 226 degrees..
If you want the fans to come on sooner, turn on the AC and the low speed operation begins at coolant temp of about 185 degrees. High speed operation with AC on remains at 235 degrees.
Factory settings to turn on the cooling fans is ON at 226 degrees in low speed mode (both fans run but are electrically configured in series so that each fan has about 1/2 of battery volts across each motor so at slower than rated speed). Fans go off at 219 degrees or once the vehicle speed exceeds 35mph. If the coolant temp kept going up the fans go into high speed mode at 235 degrees. In high speed mode the electrical configuratio is changed from series to parallel. In parallel mode both fans have the full battery voltage across each fan motor so they run at full rated speed. They revert to low speed mode once the coolant temp reaches 226 degrees..
If you want the fans to come on sooner, turn on the AC and the low speed operation begins at coolant temp of about 185 degrees. High speed operation with AC on remains at 235 degrees.
06-16-2018, 11:55 PM
#16
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06-21-2018, 09:05 PM
#17
Can you say for absolute certain that BOTH fans are running in high speed mode???
If both fans are operating in high speed mode then relay 45 CANNOT be a problem. It is requires for the drivers side fan to be able to operate in high speed mode. If you know how to read electrical diagrams then look at the one in post # 3 above and you will see that.
Here is a link to another thread that I posted some diagrams that shows power flow through the circuits for the C5 cooling for both lo and hi speed fan operation:
https://www.corvetteforum.com/forums...post1597237631
You need to double check that the drivers side fan is in fact running when the fans are in high speed mode.......
If the left side fan is not operating it could be because of relay 45, fuse #49 or the left side fan itself may have failed. It could also be a problem in the PCM where the PCM fails to provide electrical ground for the coil side of relay #45.
If both fans are operating in high speed mode then relay 45 CANNOT be a problem. It is requires for the drivers side fan to be able to operate in high speed mode. If you know how to read electrical diagrams then look at the one in post # 3 above and you will see that.
Here is a link to another thread that I posted some diagrams that shows power flow through the circuits for the C5 cooling for both lo and hi speed fan operation:
https://www.corvetteforum.com/forums...post1597237631
You need to double check that the drivers side fan is in fact running when the fans are in high speed mode.......
If the left side fan is not operating it could be because of relay 45, fuse #49 or the left side fan itself may have failed. It could also be a problem in the PCM where the PCM fails to provide electrical ground for the coil side of relay #45.
Last edited by 98-corvette; 06-21-2018 at 09:07 PM.
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c5007Alvarado (10-02-2023)
06-23-2018, 06:39 PM
#18
Disconnected fans and powered up individually with 12 volts and both fans operated on high speed, all wiring looks good.
07-03-2018, 11:59 AM
#19
Only two possibilities left.
1) Relay 44 does NOT work in its normally closed position. If you look at the diagrams I posted a link to on how the current flows in both high and low speed modes (post #21), you will see that for the fans to operate in low speed mode (fans are configured in electrical parallel), relay #44 has to provide a path to the right side fan. If the contacts in the relay are bad this could be an open circuit. You can try replacing relay #44. It is a different relay from the other two in the fan circuits. A SPDT vs the other two being a SPST.
2) The PCM is failing to provide a ground path for relay 45 so that the fans can come on in low speed mode. This could be either a PCM issue or an issue inside the fuse box. Lets hope the cause of your problem is #1 above as this one is a difficult to correct problem if it is either the PCM or the fuse box....
1) Relay 44 does NOT work in its normally closed position. If you look at the diagrams I posted a link to on how the current flows in both high and low speed modes (post #21), you will see that for the fans to operate in low speed mode (fans are configured in electrical parallel), relay #44 has to provide a path to the right side fan. If the contacts in the relay are bad this could be an open circuit. You can try replacing relay #44. It is a different relay from the other two in the fan circuits. A SPDT vs the other two being a SPST.
2) The PCM is failing to provide a ground path for relay 45 so that the fans can come on in low speed mode. This could be either a PCM issue or an issue inside the fuse box. Lets hope the cause of your problem is #1 above as this one is a difficult to correct problem if it is either the PCM or the fuse box....
07-03-2018, 10:21 PM
#20
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Only two possibilities left.
1) Relay 44 does NOT work in its normally closed position. If you look at the diagrams I posted a link to on how the current flows in both high and low speed modes (post #21), you will see that for the fans to operate in low speed mode (fans are configured in electrical parallel THIS SHOULD BE SERIAL CONFIGURATION FOR LOW SPEED), relay #44 has to provide a path to the right side fan. If the contacts in the relay are bad this could be an open circuit. You can try replacing relay #44. It is a different relay from the other two in the fan circuits. A SPDT vs the other two being a SPST.
2) The PCM is failing to provide a ground path for relay 45 so that the fans can come on in low speed mode. This could be either a PCM issue or an issue inside the fuse box. Lets hope the cause of your problem is #1 above as this one is a difficult to correct problem if it is either the PCM or the fuse box....
1) Relay 44 does NOT work in its normally closed position. If you look at the diagrams I posted a link to on how the current flows in both high and low speed modes (post #21), you will see that for the fans to operate in low speed mode (fans are configured in electrical parallel THIS SHOULD BE SERIAL CONFIGURATION FOR LOW SPEED), relay #44 has to provide a path to the right side fan. If the contacts in the relay are bad this could be an open circuit. You can try replacing relay #44. It is a different relay from the other two in the fan circuits. A SPDT vs the other two being a SPST.
2) The PCM is failing to provide a ground path for relay 45 so that the fans can come on in low speed mode. This could be either a PCM issue or an issue inside the fuse box. Lets hope the cause of your problem is #1 above as this one is a difficult to correct problem if it is either the PCM or the fuse box....
Parallel Operation:
Both fans are attached to +12V in parallel.
Low Speed Operation:
TheT
The left side in the schematic is attached to +12V while the right side fan is attached through the relays to the outlet of the left side fan and then to ground. They are connected one after the other (serial) with the voltage drop across the complete circuit at 12V with 6 volts of it being dropped across each motor since they both have the same resistance.
Bill
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wroughtiron65 (05-21-2021)