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Car Overheating -- troubleshooting cooling fan

OK, so I'm trying to track down this cooling fan problem. When I turn the a/c on, only the passenger side fan comes on.(People assure me the driver's fan is supposed to come on to. Can somebody confirm this is true? I have a 96' Honda accord LX)

Here's what I've done so far:

1. Direct power to cooling fan(driver's side) works
2. Swapped relays(both turn on a/c clutch)
3. Tested relay wires with test light(Bright as battery, 12v I assume)
4. Tested thermostat sensor A/B. The one behind the engine is so dim I thought it wasn't getting any power and the thermostat in front of the engine(top radiator hose. Green bulbous connector) was dim yet slightly brighter.
5. Tested the wire that runs from atop the compressor to the fan with test light. Looks like it's receiving no volts.(but I'll double-check)

Where do I go from here? Pictured is my multimeter that I'm not 100% confident I'm using right.(I tested the battery and got 12 volts)

*Also, there was some green corrosion on both the brass pieces of the thermostats. Does that mean the wire before the connector is the culprit?
Equus 3320 Auto-Ranging Digital Multimeter.jpg
220 x 220 - 12K


  • Both fans should come on with the a/c running. The temp sensors are by-passed when the a/c is on, so the circuit problem is somewhere else. Start at the fan relays and check that the circuit to the driver's side fan is working. Check to see if the a/c circuit is activating the relay. Let us know.
  • The circuit? Are you talking about the fuses? I checked all those and they are all good.

    Since there is low voltage on the connector wires to the thermostat I'm probably looking for some corrosion somewhere, right? Popular mechanics said that's the most likely cause.
  • Possible corrosion. But, by checking the circuit, I mean check the impedance between the relay and the cooling fan connector. This checks the wiring and the connection ends for possible open circuit issues. If the ohm reading is less than infinity, there is a circuit problem.
  • edited March 2012
    ok, I now what know the ohms sign is, I have that on my multimeter-----------Ω -- ohm's symbol

    Ok, I tested the connector by placing the positive inside the connector going to fan and grounding it. That's just a voltage check, right?

    Which connectors do I need to put which side in to test the circuit? (Also should I do this with the car on accessories II?)
  • edited March 2012
    Ok, good news I'm not an idiot. My voltage check wasn't reading right because the main ground off the battery cable to below the engine was corroded as all get out and the wire insulation was exposed and fraying!. I did the laborious task of getting it off, cleaning off the corrosion with a wire brush, snipping of the extra wire, wrapping it in half of a lb of electrical tape, bolting it back on to the ground point and now I'm picking up DC voltage on the thermostat sensors, instead of just the light. Infinitely more helpful!

    Well, the lights speak to the voltage. Thermostat A(behind engine) had a whooping .4 volts at first and at second test it came all the way up to .8 something(Woot.) Thermostat B(in front of engine) was testing at 10.58 volts...not too bad but still low.

    The positive battery terminal is in okay condition. I'll probably clean off the wires that bolt to the clamp on the battery. I thought about replacing it, that one looks tough to replace and I don't really feel like paying the dealer $70 for new battery cables. I probably won't replace it unless I can get it used.

    Updated: I tested the connector that go's to the driver's side fan. Seems now that I have a proper ground from the battery it's reading at a steady .4 volts, the same as the thermostat A, which I think if I'm not mistaken controls both fans. I shorted this days earlier and the passenger side fan came on, but the driver's side didn't.

    The wires to the relays both read 12 volts, but the connector to the fan is getting .4 volts. Am I missing something?
  • edited March 2012
  • This is why you need to check the circuit. There is a problem between the relay and the fan connector if the voltage drop is that much. Did you try running the 12V power through the relay connector with a jumper wire? You may need to run a new wire from the relay to the fan if you cannot isolate the circuit issue. This is assuming the relay is not the culprit.
  • Most likely the problem is with the fan itself. I had this same problem a few years ago with our 97 Accord and it was the fan motor. The passenger side fan is the radiator fan and is supposed to come on both by coolant temp and AC on. The drivers side fan is the condenser fan and come on only with AC.
  • The radiator fan relay is in the underhood relay panel. On the drivers side of the radiator, on the frame near the top are two relays, the relay towards the rear of the car is the compressor relay, the one towards the front is the condenser fan relay. Remove the plug.
  • Look for a blue/yellow wire and white wire. Short the two pins together and the fan should run, even with the ignition switch in the off position. If it does not, the fan is bad. Be careful, there is a yellow/white wire, do not mix this one up with the white wire.
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