Contactor Replacement

ContactorsAir Conditioner or Heat pump Contactor Replacement

Description: This is the procedure and information for replacing a contactor on an air conditioner. The specific unit in this example is a Carrier brand ground level, split straight cool system. This procedure applies to almost every air conditioning and heat pump system on the market.

What does a repair like this cost: This is a tough question to answer accurately. A lot depends on the area you live in, the company, flat rate vs. time and material and many other factors. I have seen prices as low as $150 and as high as $300. The parts for this repair are pretty inexpensive. It is a great candidate for a do it yourself person or someone just looking to save a little cash.

ContactorsWhy do I need this repair? The typical reason for replacing a contactor when the system is still running but the contacts are badly burned and pitted. They will start sticking. This means the compressor will not shut off when told to by the thermostat. The word bad is subjective. What is bad to one person is not bad to another. I personally have seen contactors burned and pitted to a point where anyone would agree it needs to be replaced. I have seen them continue to operate for another two years. Then finally one day they unexpectedly stick on. This is not particularly bad if only left on for a short period. But left on long enough it can allow refrigerant in a liquid state get into the compressor. Compressors are vapor pumps. Refrigerant in a liquid state does not compress. This can damage a compressor as it will try and compress liquid. I personally have seen this scenario come to pass, this system's contactor is replaced and a short while later the compressor dies. More than likely, the compressor was damaged when the contactor stuck. "Compressors don't die. They are killed!". A dead compressor is the symptom of another failure or problem with the system. The is not always true but is true a majority of the time.

Estimated Repair Time: 20 minutes

  • Nut Drivers/Screw Driver like this one
    nut driver
  • Wire Stripper/Crimpers
  • Not required! Gloves I prefer mechanic gloves.
  • Not required! Volt Meter

Volt Meters


  • Contactor

Single Pole Contactor.Click on the Contactor Link to learn what type of contactor you need.

  • Not always Required! Connectors...nice to have just in case.

Repair Process:

  • condenser at side of house Locate your condenser aka the out door unit. Here is the one we are working on today. It's about 10 years old. It is the one the builder put in so we can be sure it is not top of the line.
  • disconnect location Turn off off the disconnect. It is a good idea to check and make sure their is no power to the condenser with a voltage tester or meter. Here is our disconnect. It is a breaker type you may have the pull out type.
  • Breaker Panel Breakers Locate your Panel and turn off the air handler and condenser breakers. This house has two air conditioners. I am not going to assume the panel is scheduled (labeled) correctly. I will shut them both off. Also shut of the air handlers (other part of a split system located in the attic, garage or closet). That is for breakers for this house. You may only have two or one if you are performing this repair on a package system.
  • disconnect location Find and open the access panel. A good clue is if your air conditioning system has more than one cover. It is the one with the electrical warning sticker on it. Here is the one for this unit. It is held on by two screws but a trick to easy removal is loosening this the top two screws too.
  • Contactor Location Here is our contactor. This particular one is a single pole, 24 volt coil, 35 amp @ 277V contactor. Learn how to identify yours! Now if the one you have doesn't match or for some odd reason is too big. Lets stop here and get a different one. But please keep in mind it doesn't have to look exactly the same and rarely does. As long as the it is the right type, the connecting and mounting challenges are easy to overcome.
  • burned contactorsThe contacts on this contactor look bad but I have seen much worse.
  • Here is the most challenging. It is really not that challenging. How do I get all the wires from the old contactor to the new one?
    • disconnect locationFirst rule is make sure you know where they are coming from before you remove them. Now you can always use the schematic on the back of the access panel but that is too time consuming and you have to know how to read schematics. Sometimes they have worn off or rotted away. We are not going to attempt to cover this large topic here. I will tell you a little secret. A lot of air conditioning technicians cannot read schematics very well if at all. Shhhhh, don't tell anyone. Oh I am sorry if I offended someone in the trade but I know this to be true. You can learn more about verifying you have a competent technician standing at your door here!
    • The most common sense way is to draw a picture and mark them. If there are a lot of wires, I tape them together and just push them off the direction they must go back. But if you look at the one we have here. Top right all the yellow wires. Top left all the black wires. Bottom two black wires. Blue wire on the left side and a brown wire on the right side. Not a whole lot to remember but I still make a diagram out of habit. I usually write in on the inside cover with a pen.
  • Contactor mounting Remove the old unit. Typically held by one or two screws. This one is held by two on the same side. You can't see the bottom one. Now a quick side bar. You should note if the contactor being installed needs mounted different. This rarely is a problem. Usually you can get one screw in to mount the new one. I would argue this is enough if it is nice and snug. With that said, a couple of self tapping screws and your in business. I don't have these as part of the repair since most of the time it is not necessary.
New installed contactor
  • Connect all the wires. Note: It is important to make sure all the connections are tight. Loose connections will not always cause failures today but will in the future.
  • We are done now, but some of the best advice I ever received was to measure twice and cut once. This applies here too. Double check all the wires and their connections are in the right place. Verify against your diagram once more they are connected where they are suppose to be connected. Verify all the connections are tight. I like to give each wire a little tug at the base of the connection to verify this. All connections tight. Quick tip: If the your spade connectors are loose, pull them off, pinch them down just a little with your crimpers and reconnect them. This tip alone can save numerous failures. Loose connections cause failures
  • It is now time to turn on the breakers at the electrical panel. Note the disconnect is still turn off.
  • Thermostat Proceed to the the thermostat and turn it on so it calls for cooling. It is the same process you go through when you find your house too hot and you want it cooler.
  • Pulled In Contactor If all has gone well, the contactor should be pulled in. If your contactor is open, it would look like this. It is usually accompanied with a slight hum or buzz but not always. Most systems have a delay before turning the condenser on so be patient.
  • Put the condenser cover back on air conditioning condenser.
  • With the contactor pull in, turn the disconnect back on. The air conditioner will come on and run.

You just saved big bucks and extended the life of you air conditioning system!