Battery Draining – Found Relay Closing At Key Off

[Rusty]

Hi guys (and gals),

I have a 2001 Honda Civic and the battery keeps draining every day to few days. The battery is new, recently replaced, and the alternator is charging and was tested good by AutoZone.

I found the relay that controls the AC Compressor will hang closed with the key off/engine off. This makes the compressor engage, and is what I believe is causing my battery to drain. Would you agree? I would have thought this relay, which is located in the under hood fuse box, would have not had any battery power if the key is off and/or removed. Is there some other problem going on here? I don’t believe I’m having trouble with any other relay.

I appreciate your thoughts. It would be great if I could get out of this one with just a replacement of the relay.

Topic

[Its me]

Try doing this to confirm…

[Rusty]

Thanks, ToyotaKarl. I actually did try that previously, but got no real results. I was not able to get the relay to switch on while doing this test. I can try again, but it seems to be intermittent. If 12 volts is supposed to be supplied to that relay even with the key off, then I can go ahead and replace the relay. Does anyone know if 12 volts should be present at the AC compressor relay at all times?

[college man]

With the key off. there should be know power to the compressor
relay.If power is present.I would suspect the ignition switch.

[twiggy]

Here is a partial wiring diagram. As you can see, there should be no power to that relay with the ignition switch off. I would measure incoming power with a meter to verify the anomaly that you suspect.

Attachments:

• wiring2001civic.png

[Tom]

I am a sticker for details, especially when we are talking about electronics.

I don’t recall the OP mentioning anything about WHICH PIN on that relay was getting power with the key off.

OP, where did you measure that 12V with the key off? Was it at the clutch hub, or at one of the pins in the relay socket?

Unless you all are reading that wiring diagram differently than I am, pin #2 on the compressor clutch relay is getting a constant 12V via fuse 1(20A)in the under hood fuse box. That 12V will be present with the key off. Pin #3 gets a 12V signal with the key in the on position via fuse #14 (10A) in the under dash fuse box. Though it doesn’t show the rest of the diagram here, I will assume that pin #4 is grounded when the AC switch is on. Pin #1 is 12V out to the compressor clutch. If there is 12V at pin #4 with the key off, then there is a problem. 12V at pin #2 with the key off is normal though.

[twiggy]

Sorry, here is the whole diagram:

If the relay was physically sticking, 12V would be present on pin 1 of the relay which would quickly drain the battery, because, as pointed out, pin 2 should always have power (12V).

Attachments:

• civicHVAC.png

[Daniel]

The easiest way to hunt down a parasitic draw is with a test light or multimeter.
With a multimeter:
-disconnect the negative terminal from the battery
-connect the black multimeter lead to the negative battery cable from the car (that you just disconnected)
-connect the red multimeter lead to the negative terminal on the battery
-(with the key off) it is normal to see a draw of two or three milivolts. If you see more than that then pull the fuse for the compressor. If you see no change in your draw voltage, put the fuse back and continue these steps with every fuse until you see your voltage drop.

With a light tester the procedure is the same, you just don’t have the black and red leads on the light tester.
-disconnect the negative terminal from the battery
-connect the metal tip of the tester to the negative battery cable
-connect the lead wire from the tester to the negative battery terminal
-the light on the tester will (most likely)turn on but should be very dim. If the light is bright then you go through the fuse pulling process until the light goes dim.

If you don’t have either of these tools, the light tester is the cheaper of the two, but the multimeter will be slightly more useful and accurate for this job and future jobs.

[Rusty]

Thank you all for this info. I think I have enough to go on for now.

I have not measured any voltage directly from the relay or the pins in the fuse box. I have only noticed that the relay is closing and the compressor clutch is engaging when the key is out and car is off. It does seem to happen mostly when the car/relay is warm.

If you’re like me, when you are trying to help someone you want to know the outcome. I won’t be able to get back to you until later in the week or possibly this weekend, but I thank you for this information.

Thanks!

[Author]

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