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I replaced the contactor and the unit still doesn't work

I have a 2 pole 24 volt, 30 AMP contactor. I am receving 23 volts when the unit is switched on at the termostat. I have 120 volts at both poles entering the contactor. I have replaced the contactor with a new one but it still doesn't work. When I manual depress the contactor the compressor and fan both turn on. Is it possible the new contactor is defective as well.

Many thanks in advance.

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  • Zeeshan Alam Jul 14, 2009

    More Details on my Problem: my new 2-Pole Contactor ... I have 120V on each pole coming from the fuse box into the Contactor. When the thermostat is set to "AC ON", the coil is receiving 23 volts on each of the two sides of the coil. However, the contactor is not "pulling" automatically. If I press the "pull" switch manually with my finger, the FAN and COMPRESSOR turn on ... if I remove my finger the "pull" switch comes back out and the FAN and COMPRESSOR are turned off. ... MY OLD CONTACTOR was doing the same thing and I was thinking that my CONTACTOR was bad ... so I changed it. ... but the new one does the same thing. ... now what

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Are you getting 24 volts at the contactor coil? If not check your control voltage wiring to the unit. If all is good check refrigerant charge, you will need gauges for this, compressor can be held out due to low pressure, also unit can be out by the high pressure safety switch which is normally reset manually.

Posted on Jul 14, 2009

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No but you could check to make sure your common has a good connection to the transformer. if you think the contactor is bad put a ohm meter across the coil to see if you have continuity.

Posted on Jul 14, 2009

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Magnetic relays commonly known as definite purpose contactors are used in a variety of different applications throughout the HVAC and Appliance world. They can have anywhere from 1 pole or up to 4 poles or more. The coils on them can be 24 volt 120 volt 240 volt or even 440volt and better.02c6373.jpg Their main job is to power compressors and fan motors on various equipment. On a home unit the contactor is almost always a 24 volt, 2 pole, 30 amp one. Some smaller units have what is known as a pole and a half. or 1.5 poles. The coil pulls down only one side of the contactor, while the common leg has a straight bar across it. On home units smaller thermostat wires connect to the 24 volt coil powered by a transformer.When the temp rises the thermostat calls for the contactor to yank down and power up the compressor and fan outside. If those small wires are chewed up by an animal or a weed eater then power to the coil cannot do its job. Very often the 24 volt coil on the base of the contactor just dies. A couple videos I found on line will give an idea of various types used in home units. A guy had a unit which would not shut down because of fried welded together contacts. He did an autopsy of the old part. I thought it was cool.

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on Aug 21, 2010 | Heating & Cooling

1 Answer

Contactor diagram ruud ac


The 030 model is a 2.5 ton system, so it is not going to utilize a very big contactor. If you're not that familiar with wiring, take a picture of the contactor, turn the power off to the outdoor AC, make notes on where all the wires are attatched & remove all the wires. (Note, you also need to turn off the indoor unit which supplies 24 volt control voltage to the outdoor unit...in other words, turn off you furnace power). Remove the contactor, take it to a local electrical supply house & they will match it. Replace it by reversing the above steps. If you are deadest on ordering online, look @ the white sticker on the side of the contactor in your AC for the ratings. Really the only thing you need to find is the VA rating. On a 2.5 ton system, it is probably only about a 20VA. Get a double pole contactor (brand doesn't matter), 24 volt coil, with the rating on the existing contactor (if you are not sure, a 30VA contactor will do) When it comes in, plug & play.

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Butters


Based on your description there should be 2 contactors. One is the contactor that controls power to the welder primary winding, this one should be quite large compared to the other one, the other controls the 24 volt (most common) supply to the wire feed speed control board and gas solenoid. If you do have 2 of these contactors, the 24 volt contactor may supply the control current to the larger contactor..

If blowing out the cabinet has not helped, and at this point it is not likely, the 24 volt contactor should be replaced. If a sealed one is available I would upgrade to that style. The ratings should be embossed on the contactor somewhere, otherwise your control voltage should be 24 volts, use a meter just make sure you are in that range, US, UK and Euro standard share some common specs. You may have a 2 pole or 3 pole type- it depends if the gas solenoid is powered off the same pole as the motor control board, or if it is powered by it's own pole. These would be the "N/O" contacts, and all would have current supplied by the 24 volt supply/control supply. The larger contact coil winding would be on it's own pole. Contacts should be rated at 15 Amps minimum

Replacing both contactors at the same time if so equipped is a cost effective bit of maintanence.

If you have only the single 24 volt contactor, the tip will be live at all times and it will only be the gas and the wire feed control board that would be switched by the contactor.

Again, based on description, I would replace the 24 volt contactor. Contacts should be rated at 15 Amps minimum

I would also just check the gas solenoid with a jumper wire to make sure it opened and closed as it should.

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1 Answer

I have a 1991 model gmn100-4 furnace and air con power supply 115 volts 1ph60hz less than 12 amps my problem is when fan moter kicks in the air unit does not i checked and theres power from breaker box to...


Hi Jimmy, yes, I bet it is hot with that high humidity. From what you are saying, it sounds to me like this pusher switch is the contactor at the out door unit. It has the power lines going into it, and out the other side. It will have contacts on it that you can push down, is this what you are talking about when you say pusher switch? The indoor unit is 115 volts, you are right about that, but the outdoor unit contactor/pusher switch is 230 volts. You should have a box mounted by the outdoor unit for high voltage. Most all of the disconnect boxes have 2- 30 to 35 amp fuses inside them. You may not see them, so pull the plug and the plastic cover in the box to see if you have them. If you do, you may have blown a fuse. Replace both of them. This box is powered by a breaker at your main panel also. You will have a double pole breaker and make sure its not tripped. This contactor has a 24 volt coil on the bottom of it and is energized by the thermostat which closes the contacts to send power through to start the unit. You have to have 230 volts there. Turn the stat on cooling and go out to see if the pusher/contactor switch is energized. If so and the unit is not on, you have no high voltage there to run it, so check for fuses and the main breaker. You have power to the indoor unit, but not the out door unit. Start here and do these checks. Keep me posted on this Jimmy, and get back to me if this does not start the unit or if you trip a breaker. I will be watching for you. We will get it going. If this does the trick, be sure and rate me kindly as I know you will. Keep me updated by my user name below.
Sincerely,
Shastalaker7
A/C, Heating, & Refrigeration Contractor.

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You need 24 volts going to the coil of the contactor. If you do not have 24 volts, you will need to trace the wiring back to see where you are losing it from. Try placing your voltmeter at C & Y coming from your air handler. If not, go to your air handler and test for 24 volts ac at C & Y coming from your thermostat. If you do not have 24 volts coming from your thermostat, there is either a problem with the thermostat or there is a problem with the wiring between the thermostat and the air handler. If you have 24 volts at the air handler coming from the thermostat but you do not have 24 volts at the outdoor unit coming from the air handler, then you have a problem with the wires between the air handler and the outdoor unit.

I hope you find this information to be very helpful to you moving forward. Please leave a rating. :-)

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I would replace the contactor if you are getting 24 volts to the contactor and it isn't engaging therefore the magneto on the contactor is out and the contactor will need replacement. If you don't have 24 volts at the contactor then the transformer that sends the 24 volts is bad and will need replacing

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Usually when you replace the contactor, you do it by the number of poles and the amp rating on the contactor and the coil voltage,
for instance most AC contactors are 2 pole, 25 to 50 amp and 24 volt coil.
If you look on the contactor you have it should have the amp rating on the side and coil voltage is usually there also and you can look at the contactor to see how many poles.

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I don’t believe changing the contactor to a double pole contactor will solve this problem. It appears by your description that bugs are being attracted to the contact points on the contactor. Changing to a double pole contactor will not eliminate that problem but only provide another contact point for the bugs to be attracted to. The most effective solution would be to replace the current contactor with a sealed design where the contact points are totally enclosed. Enclosed contactors are completely enclosed protecting it from bugs and dirt. These type of contactors are available in the single pole design so no further wiring modifications are needed. You can consult a professional A/C service company like mine for more information and assistance.

Hope this helps. Let me know if there's anything I can do for you!

Sam, The Service Expert
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