A burned contactor

This one shows a contactor that may have caused a compressor failure diagnosis. This video is part of the heating and cooling series of training videos made to accompany my websites: www.graycoolingman.com and www.grayfurnaceman.com to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages can be lethal, the fuels are highly flammable and high pressures are used. Know your limits.

[@StephenRardon]

Always enjoy your point of view.

[@kurtwm2010]

I replaced my capacitor today, because my house fuse for the A/C kept tripping every about 24 hours. However after replacing the capacitor the unit would not come on. I watched as the contactor kicked in and immediately released. Mine looked exactly like the one in your video. Of course, I replaced it because of the blackened contacts and not the discoloration. In any case all is well, the house is cool again and my wife let me move out of the dog house.

[@DOLRED]

If you are careful with the spring, the tips can be removed and reset for inspection. If the contact surfaces are badly pitted and carbonized (Black), it is toast. I have sanded these down with light sandpaper (400), etc. If enough silver is present on the head, they should be OK as long as the surface is somewhat flat/even. I replaced contacts as a maintenance guy years ago, sometimes the electrical energy picks a spot on a contact surface and literally eats away at the same location over and over--usually on the edges (Probably because the contact points are not even when closed). I have believed contactors are likely responsible for most single phase damage but I know little about that side of the subject to make a public statement.

[@RobHVAC]

Great info Gray.

[@dcrickerson9775]

Thanks for sharing GFM.

[@Fresh123472]

Nice video keep it up.

[@vanessaa583]

That's amazing... Someone could easily replace a unit for thousands of dollars for a part that is worth $10 bucks...

[@56rmax]

Thanks

[@starlite528]

I have a single connection contactor like this in my compressor at home. I was surprised to see it only breaks one leg of the circuit. Would it be a good idea to replace it with a contactor that is a double pole? My compressor starts up with a big thunk. I was looking in to maybe getting a soft starter for it.

[@samacochan]

I have exactly the same contactor which caused the air conditioner failing to start up. Can't figure out the model and spes. Please help me.

[@grayfurnaceman]

You need amp draw found on the side of the contractor. Number of contacts. Coil voltage (usually 24 volts). GFM

[@samacochan]

Thanks. Just figure out that it is a Honeywell 8242A 1255. No longer in production.

[@grayfurnaceman]

Any brand will do with the right configuration. GFM

[@rigel4379]

Im going to check out the compressor today after work. It is single phase. Im going to make sure the resistance values add up. What else should i check?

[@hvacrjunky6119]

I have had comp that were not showing a ground but the contactor was welded shut and the breaker tripped. When I replaced the contactor it would weld shut and trip the breaker as soon as power was applied. Do you have any idea why this is happening?? I believe that the comp windings are bad but not ground and carry such a large current upon start that it welds the contactor points closed and overloads the breaker.....???? But I don't really know, I have seen this multiple times. Thanks for the vids?😎

[@grayfurnaceman]

+HVAC/R Junky It is possible to have a dead short in the windings and not be grounded. Even though the breaker kicks off, the amp draw could be in the thousands. GFM

[@hvacrjunky6119]

+grayfurnaceman A dead short, I will have to look it up. Interesting. Thanks

[@rigel4379]

My contactor was visibly burnt. I replaced it. It worked great for a day. Then it stopped working with same symptoms (wont start). Any ideas anybody?

[@grayfurnaceman]

Will need much more. Does the new one close? Is power available? GFM

[@rigel4379]

its got a cover on it so I cant see if it closes. but I can remove it and check. It is arcing at the terminal that goes to the compressor. This is the same terminal that was burnt on the last contactor. It is getting 240V coming into the contactor.

[@grayfurnaceman]

Could the compressor be locked rotor? GFM

[@nkhvnkhv7763]

Ah! Foolish !!!😂😂😂😂

[@rigel4379]

Im going to check out the compressor today after work. It is single phase. Im going to make sure the resistance values add up. What else should i check?

[@grayfurnaceman]

You need to check amp draw upon startup. Should be with in the RLA on the model plate. GFM

[@rigel4379]

I checked the amp draw and it was drawing no amps so I took off the cover to the contactor to see what it was doing while the thermostat was calling for cooling. The contactor was stuttering and arcing--it was trying to pull in but did not. I pushed the contactor in with my screwdriver and viola! Unit runs fine: the amp draw is around 10 (the unit specs for 14) ; the fan is running and the unit is blowing cold air into the house. Problem is, as soon as I release the contactor plunger the unit shuts off. I am beginning to suspect the new contactor I bought. Not all the specs on my old contactor match the specs on the new one. Old specs are FLA: 25; LRA: 150, 50, 40 RES: 30. The new specs are FLA:30 LRA:150, 75, 50 RES: 40. You think the new contactor might be the cause?... by the way the resistance values on the compressor add up properly.

[@grayfurnaceman]

The contactor could be bad. Check the voltage at the contactor coil. If it is below 24, the control voltage is the issue. GFM

[@rigel4379]

there is no voltage across the coil were it should read 24. there is 240 v coming in and 240 v coming out but strangely there is no voltage through the switch when I have it pushed in with a screwdriver... While I was testing the contactor the unit started working for a minute without me holding the contactor in with a screwdriver. During this time I noticed that there was 24v across the coil

[@rigel4379]

+Sam Fry yeah. I tried jumping my time delay and fried my transformer. Im going to replace the transformer and the time delay this week. I can see nothing visibly wrong with the time delay and im not sure how to test it