I wanted to title this: Outside unit running, but thermostat is off but I'm 99% sure its the contactor unless someone here says otherwise.

Thus my real question: which contactor should I buy? I typed in the part no. on Amazon but I'm experiencing death by choices. No where on my current contactor can I find the words 1 pole or the amperage. The variety of contactor choices I have are making me nervous. Heres the pic of my current one enter image description here

One last question, does manufacturer matter? Do I buy Siemens only?

Everything works fine by the way the fan just runs non-stop. Just fyi I've replaced the capacitor and a fuse on the control board this week.

  • That looks to me like it is a 1-pole contactor. Is your unit at 240 V or 120 V? I am pretty sure my 240 V condensing unit has a 2-pole contactor Commented Jul 27, 2019 at 15:37
  • So the outside fan is running continuously. Is the compressor running continuously too? Is the larger refrigerant line always cold. Is the air coming out of the vents inside always colder than the room? Commented Jul 27, 2019 at 16:18
  • Does the contactor operate the inside fan, outside fan, or the A/C compressor? Commented Jul 27, 2019 at 16:22
  • Also, don't buy the junk on Amazon. 99% of it is the "Amazon Marketplace" flea market, which is straightlined from Chinese counterfeiters or the QA reject line of the legitimate parts. Do not buy electrical parts that say "Sold by some-name-here and fulfilled by Amazon" (under the Buy button), that is Amazon Marketplace. Ditto eBay, ditto alibaba/aliexpress. That's the reason you're experiencing death by choices, you are including that trash. Commented Jul 27, 2019 at 16:25
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    Is it possible that you switched L1 and L2 when you changed the capacitor? So the compressor works as before, but if the fan was supposed to be on L1 it is now on L2 to neutral and running continuously. This is just a though and may not be possible. Commented Jul 27, 2019 at 16:29

2 Answers 2


If the condensing unit fan is 120 V (L2 to neutral), then the fan would run continuously. But unless someone changed wires in the unit it should be connected to L1. You may be able to unstick the contactor by tapping on it with a (non conducting) rod or other object.

If the current contactor is original, you should be able to get a correct replacement by cross referencing the Siemens number.

The info on the sticker "CONT1P025024V" presumably means 1-pole ("1P").

EDIT When you changed the capacitor did you possibly switch L1 and L2? The contactor may be OK.

  • I have never touch the contactor and when I replaced capacitor I hooked up the wires exactly as they were. I'll try taping it... Commented Jul 27, 2019 at 17:40
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    You are going to waste money and time by concluding without proper testing that the contactor is at fault. Commented Jul 27, 2019 at 19:45
  • Thank you Jim! You were right I would have wasted my money and time, come to find out I wired the ac wrong to the control board. I did red wire to R so it was getting constant power! Instead that red wire need to go to Y alongside a yellow Rosenthal goes to the thermostat so hopefully my ignorance is understandable... Thank you again and you saved me from a pointless purchase! Commented Jul 28, 2019 at 0:35

The L1 and L2 designates the two feeds. The contactor is a one pole contactor with a shunt. The voltage rating is 277volts. The FLA designates full load amps, 25 Amps, which is the max rating for the contactor with inductive load. The LRA designates locked rotor amps, 150 amps, which is the max rating for motor startup, and the res amps, 35amps, is the max amp rating for resistive load like lighting. The coil voltage is 24v and is fed from a transformer in the air handler. Your compressor would be considered inductive load.

You don't have to go with Siemens but get a good one... remember, you get what you pay for.

Also, your fan in the compressor, should not be running all the time, only when the compressor is running. Good luck.

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    OK I see the L1 and L2 connections but it looks to me like the L2 is just straight through which I would think would be called a one pole contactor. If both the compressor and the condensing fan are both 240 V, then there would be no need to interrupt both L1 and L2 to shut them off. There is presumably a 2-pole switch on the wall next to the unit to disconnect both L1 and L2 to allow safe work on the unit. Commented Jul 27, 2019 at 16:00
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    See the info on the sticker "CONT1P025024V". Presumably the "1P" means 1-pole. Commented Jul 27, 2019 at 16:06
  • I see contactors that say "30 amp" and "40 amp" but not 35? Should i round up Commented Jul 27, 2019 at 16:21
  • The 35 amp is for resistive load..... 25 fla is what you're looking for. If it's not available you can go with a 30 fla. Your compressor should have #10 awg cu wiring.
    – JACK
    Commented Jul 27, 2019 at 16:30

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