Cooling fan question...
03-09-2019, 06:02 PM
#1
Heel & Toe
Thread Starter
Cooling fan question...
Sooo here's my question: I have an 85 Corvette with HD cooling. When the temp hits an indicated 232, only the aux (pusher fan in front of the condenser/rad) fan cycles, the main fan under the hood does not. Going thru the repair manual (chart C-12B-coolant fan inop) everything functions as designed. If I jump the ALDL, it kicks on, if I disconnect the ac press switch, it runs....When I bought the car in November, I noticed the relay had been replaced with an aftermkt one. I've since replaced the pigtail & relay with the correct type, verifying that the wires were routed correctly. Is it normal for the aux to run first? The manual's description of the circuit operation is vague to me regarding the sequence...HELP!!!
03-09-2019, 07:31 PM
#3
Drifting
aux fan has a coolant temp sensor on the driver's side bank....not associated with main fan.....main fan should come on with a/c.....or when the ecm says so.....
03-10-2019, 05:47 AM
#7
Heel & Toe
Thread Starter
Because the main fan runs with the ALDL jumpered, the ECM is capable of controlling the fan, and the circuit is intact. So it's the programming of the ECM (the "chip"), or the coolant temp input to the ECM. I'd check the resistance of the CTS vs the chart in the FSM. Or just change it. A Delco CTS should be less than $20 pretty much anywhere. Otherwise, something is fubar in the chip.
03-10-2019, 11:52 AM
#8
Drifting
I had a different problem where the CTS not telling the ECM to lean out as car warmed up causing it to stall. It was throwing a 15 code pointing to the CTS. I unplugged the CTS to confirm it was causing the problem.
After unplugging it I found that the fan would run continuous regardless of coolant temp. You may want to experiment by unplugging yours to see if it changes anything. Of course if it is a problem with the fan itself nothing will change for you.
After unplugging it I found that the fan would run continuous regardless of coolant temp. You may want to experiment by unplugging yours to see if it changes anything. Of course if it is a problem with the fan itself nothing will change for you.
03-10-2019, 02:11 PM
#9
Drifting
03-10-2019, 06:56 PM
#10
Heel & Toe
Thread Starter
The parameters for 14 and 15 are generally only met with an open or shorted sensor circuit. Skewed resistance conditions generally won't set 14 or 15, because the sensor voltage is still within the acceptable range, but "wrong". I have a Lot of miles (750,000+) in GM vehicles with this sensor and I have yet to replace one for "out of range", or for any other reason than mechanical damage by breaking it while working on something else. I don't think it's going to be the sensor.
What PROM is in it?
What PROM is in it?
03-11-2019, 05:52 AM
#11
Safety Car
The main fan should come on before the aux fan. The main fan is programmed for 228 degrees and the aux fan is 238 degrees. You need a scanner to determine what the computer is seeing. It is possible that the computer which is being sent temperature information from a separate sensor does not indicate 228 degrees when the aux fan kicks in. The main fan nay be coming on late and the aux early, both are run from separate sensors. It is also possible that somone programed the main fan to come on latter but I doubt it.
A scanner would really help with this issue.
A scanner would really help with this issue.
03-11-2019, 07:49 AM
#12
Heel & Toe
Thread Starter
The main fan should come on before the aux fan. The main fan is programmed for 228 degrees and the aux fan is 238 degrees. You need a scanner to determine what the computer is seeing. It is possible that the computer which is being sent temperature information from a separate sensor does not indicate 228 degrees when the aux fan kicks in. The main fan nay be coming on late and the aux early, both are run from separate sensors. It is also possible that somone programed the main fan to come on latter but I doubt it.
A scanner would really help with this issue.
A scanner would really help with this issue.
03-12-2019, 08:03 AM
#13
Heel & Toe
Thread Starter
Problem solved....took a deep financial risk (all of 16.00), replaced the CTS with a Delco, at 228 the fan kicked on, so I guess the original was getting lazy....
03-12-2019, 09:35 AM
#14
Drifting
I still have to replace my CTS, but I've been lazy because my 91 runs fine with it unplugged (except for fan running constant). Where did you pick yours at and what was the part number?
03-12-2019, 11:08 AM
#15
Heel & Toe
Thread Starter
The following users liked this post:
CorvetteRules (03-12-2019)
03-12-2019, 11:09 AM
#16
Heel & Toe
Thread Starter
03-12-2019, 02:15 PM
#17
Safety Car