This 2006 Chevrolet Cobalt came in with the complaint that the a/c would not cool very well. Particularity in city traffic. The compressor comes on sometimes. More so when a cold engine is first cranked. The system seemed to work okay if it was turned on after achieving a speed of 50+ mph. I had the benefit of looking at engine data on my scan tool so I could determine the base problem from the driver’s seat. The refrigerant system high side pressure was too high. Data also indicated that the cooling fan had been tuned on. I never heard it come on from the driver’s seat. Looking under the hood I could see that the fan was not on even though scan data showed that it should be. A quick check with bidirectional controls and physically checking the related fuses and relays did not find a problem. This Cobalt has the 2.4 liter VIN “F” engine.
I disconnected the fan motor’s harness connector and pulled it up for better testing. I also slid the split loom back slightly so that I could identify the wire colors. The black wire is ground for both speeds of the engine cooling fan motor.
That wire should have a constant ground on it. I clamped my test light to battery positive and lightly touched the exposed end of the terminal attached to the black wire. No light indicated a complete lack of ground on that terminal. If the light had illuminated, it would indicate some sort of ground being present but the testlight would not be able to indicate the current strength. More testing would have been needed.
Opening the split loom a little bit more revealed an in line diode. The diode is installed to protect the low speed relay contacts from arcing damage when the low speed winding cycles off as the high speed winding is cycled on. The motor has high and low speed windings. Basically two motors in one housing. When the high speed winding is activated the low speed winding will work in reverse and act as an ac generator. That ac voltage will damage the low speed relay contacts during the time they are trying to open. It has nothing to do with the actual operation of the fan motor. It just protects the relay.
I searched through component locators in order to find the physical location of the ground terminal end. It is listed as ground connection G111. The locators state that the G111 terminal should be “At the front of the engine compartment, attached to the front of the engine block, directly behind the cooling fan”. I could not find a wire attached to ground that matched the size and color of this wire. I did notice a wire that matched the look of the wire I was looking for attached to the starter battery post.
I am pointing to it in the picture below with a long screwdriver.
I removed that wire from the starter battery post and pulled it up towards the top of the engine. There is a ground stud in that area that has multiple ground wires attached to it. The cooling fan ground wire would not reach to that location. I used my multimeter to confirm that it was the correct wire that I had been looking for.
I found a threaded hole on the side of the block between the starter and the a/c compressor. I attached the ground wire to the block with a new bolt.
I also noticed two empty bolt holes on the bottom of the oil pan among other small details that pointed to an engine swap.
What happened was the original engine failed and a used one was installed. Since the cooling fan ground wire has the same sized ring terminal as other wires that attach to the starter battery post and it actually looked like it should go there, that is where the engine installer placed it. The PCM and relays were working correctly supplying power to the fan motor. The fan motor was good but would not work due to a lack of ground. I am very surprised that the vehicle owner had not been complaining about the engine running hot.