Troubleshooting and testing the HVAC contactor Part 7

Describing the different failures related to contactors used in heat pumps and air conditioners
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.

[@natashamarie4134]

You just saved me a service call to an ac repair place. I cleaned the contactor and now I have ac again. Thank you

[@grayfurnaceman]

Welcome GFM

[@defroyh]

Thanks for this video. I had a contactor that was welded closed so my unit never stopped and was all iced over. Thanks to your video i was able to diagnose the problem, procure a replacement, install it, test it, and save a buck. I really appreciate it!

[@ogpa6536]

Well you saved me a butt load of cash!!!!! Thank you for taking the time to educate others. Not only was I able to determine the cause (a bug) I was able to learn about a trade I had not idea about. Thank you so much sir!!!!!

[@kellihunter4791]

Your video was perfect! I didn't even know what a connector looked like, but your video was clear and to the point, thank you! Tonight we'll be warm 😊

[@grayfurnaceman]

Welcome GFM

[@stevehenderson9074]

Excellent video, short and straight to the point. Thanks again GFM

[@danielearnhart8598]

Worked for me! Ended up having a bug stuck in the contactor just like you said! Thanks a lot!

[@mikeraphone9317]

Great video, the pain you relieve in the summer time can't be underestimated, thank you.

[@grayfurnaceman]

No one has ever given me that compliment. Thanks GFM

[@ivansilva9267]

You are a genius! Ant was crushed under contacts. Cleaned with a qtip and alcohol, started back up again. Surviving Texas weather. Thanks!!!

[@grayfurnaceman]

Not genius. Just seen a lot of failures. Glad it helped. GFM

[@Jizle05]

So informative and you explained everything very well and clearly. Thank you!

[@r.d.ontheroad-1094]

You just saved me a lot of money! Thanks, I do appreciate your help! Mine , I just tapped it a few times, it wasn't welded, but it took off! Thanks!

[@skatershaner]

Thank you for this great video. Very thorough.

[@drewkroeker1454]

Very amazing video. Thanks for really going over most everything!!!

[@Bub61fd]

Plain and simple to understand, excellent presentation for a 70 rear old wannabe, never to old to learn, Thanks

[@grayfurnaceman]

Welcome GFM

[@michaelgramling8069]

Thanks for the vid, I had been checking voltage using chassis ground all along (newbie). Turns out it was just a fuse, what a relief, thanks!

[@grayfurnaceman]

Michael Gramling That chassis ground will get you in trouble with 240v. Glad you got it.GFM

[@intelin123]

How does it get you in trouble

[@lakai1131]

Thanks for the video. Probably saved me a few hundred. I had the bug stuck in the contacts.

[@stuartmorris1967]

thank you so much for the diagnostic steps... mine was just a dirty contractor and it started right up.

[@grayfurnaceman]

Glad you got it. GFM

[@noahpuckett4851]

You make a very good video. I learned a lot from this video, please make some more on tracing electrical through heat pump system thank you very much, very helpful.

[@rolandvz71]

It was the breaker outside that feeds the unit...getting 240V incoming and w/breaker closed getting 120V. Replaced breaker w/one from a big box store and she is now off and running! THX for all the good advice!

[@backyardtoolreviews9179]

awesome video love how you set up senerios my buddies had the last issue open coil thank you!!

[@grayfurnaceman]

Welcome GFM

[@timcartwright5442]

The video was a great help. Had ants in my connector. Cleared them out and it was good to go

[@derricksmith307]

AMAZING VIDEO!!! I wish I would have taken a picture because I did have a little bug in the contactor! Thank you so much I was able to cancel the $80 service call!

[@grayfurnaceman]

Glad you got it going. GFM

[@simplyjunk9775]

Fantastic video - just saved me a lot of grief/money. Thank you!!!

[@grayfurnaceman]

Welcome GFM

[@viktortsoi3994]

Thanks furnaceman! Your videos are very helpful. Especially for hvac apprentices like myself!

[@grayfurnaceman]

Welcome GFM

[@omarimordechai8589]

i guess I am kind of randomly asking but do anybody know of a good place to stream newly released movies online ?

[@reidtommy7352]

@Omari Mordechai flixportal =)

[@omarimordechai8589]

@Reid Tommy Thank you, I signed up and it seems to work :) I appreciate it !!

[@workingshlub8861]

your videos are a lifesaver thanks.

[@JeffLifeInReview]

Always find these videos so helpful

[@grayfurnaceman]

Thanks for the support. GFM

[@Cotten55]

I love you're videos and voice! Excellent videos!

[@frontiermarvin71]

yes! yes!yes! grammy award to you! exelent video!! love it ! learning a lot and also the questions are graet ! thak you also for anwser them!!

[@hero2006]

Great video. Thank for sharing the knowledge. 👍

[@billdance6711]

nice videos bud. Straight and to the point. thanks

[@rafiekjhaw8594]

Yes man that was the best troubleshooting video

[@RyanWilliams-xz6ye]

I had a bug in the contactor. Your video saved my ass. Thanks.

[@grayfurnaceman]

Welcome GFM

[@kazuma_gaming9165]

wow thanks a million. I actually have a funny predicment which caused this problem. Now I pinpointed the issue you're awesome!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[@Diabolical05]

Old video, but i really appreciate the upload.

[@270billycraven]

This is very well explained thank you sir

[@sietafak]

Great video! Just tested my contactor and 0 volts on the out side. When I first opened the box there were quite a few dead ants on there. Blew it with compressed air but no change. Got a $20 replacement, hopefully we'll be up and running soon.

[@grayfurnaceman]

Mr. Rat Good luck. GFM

[@RJP7093]

Did new contactor work?

[@somap8380]

Thank you Gary.

[@grayfurnaceman]

If you have 24 volts at the coil and the bar is not pulled down, the coil is bad. If you do not have 24 volts, the problem is elsewhere. Such as: no 24 volt power, thermostat not closed, a possible low pressure control open, a loose wire. What you must do is measure for 24 volts at the source, then continue though the circuit until the voltage stops. Remember, there is lethal voltage here. Hope this helps. GFM

[@grayfurnaceman]

The contactor could be stuck closed. If the power is off to the low voltage, such as turning off the power to the furnace, the contactor is probably stuck. You can shut off the power to the outdoor unit, then manually break the contactor loose. The contactor then needs to be replaced. Hope this helps. GFM

[@richardshoemaker1096]

You said one thing in this video, "don't use the ground to check voltage" I was and after viewing this I went back and and did check just like you showed and there it was. Turned out the contacts was burnt so I used a small file and touched them up. Fixed for 0 dollars!!! woohoo! TY

[@grayfurnaceman]

Welcome GFM

[@edsmith6504]

As a pinball guy, clean your contacts and look for a new switch in the meantime. ;)

[@PBS-nm1uu]

this is the best presentation i have seen thanks !!!!

[@grayfurnaceman]

Welcome GFM

[@grayfurnaceman]

Yes. Feed back thru loads are common. Also, when using 240v you may always get 120v to chassis. Hope this helps. GFM

[@benjiedelossantos9001]

Excellent video!!!!

[@donshaver5405]

thanks that was informative answered a question i had again thanks

[@JakeB7734]

Over 9 years later and still helpful -- Fire ants really do ruin everything. I've got cool air again but I've ordered a replacement contactor because I didn't like how fouled the old one had gotten inside.

[@DavidLee-ts7xe]

great video

[@jonesacnaples]

Very good explanation. Thanks

[@tjross1313]

Thanks for the great video. We've been without our air conditioner through the hottest part of the summer and with elderly house guests coming by often, it's been really hard on them. I put in a new capacitor and hoped that would start the thing up (the other one was confirmed dead with my multimeter), but that wasn't enough to get it going again. I've played around a little more and using a tester can see that all my wiring is live, so no problems there. I previously didn't look at the contactor in any way, but just tried to push in the switch and voila, it all started up which is a huge relief (I hope) because I was thinking it might be a bad control board, or my fan motor was shot, or maybe the float switch in my condensate pump was fried, or something worse. Anyhow, I guess I'm going to order another contactor and put it in there, hopefully that'll make the difference. I did use compressed air to see if perhaps I could clear some dead bugs from inside, but to no avail - it's still not doing anything.

[@grayfurnaceman]

Before changing the contactor, I would want to test voltage at the coil of the contactor. Voltage on a call for cool, bad contactor. No voltage, some other problem. You could have low charge which could shut down power to the contactor coil if the unit has a low pressure switch. GFM

[@Mark622111]

One of the best videos I've watched so far....simple and straight to the point. I'll follow these tips but what if I don't have 24 volts to the contact?

[@grayfurnaceman]

Mark Gaarz Then you need to look for a control problem. Thermostat not passing power, pressure switch open in outdoor unit. Hope this helps. GFM

[@antoniokristler6973]

Check your safety switches my dude. Low pressure, float switch, high pressure. Anything in series with your low voltage from your board out to your contactor.

[@grayfurnaceman]

What happens when you go to gnd, you can get feedback through the components if only one side of line has an open. GFM

[@sourkraus1]

You probably don't need another "bug in contactor" tale, but that was my issue! I really can't believe it. My wife and kids weren't as impressed as I was, but that's OK. ;) Thanks again!!!!

[@grayfurnaceman]

Common response from family members. Such fools! lol GFM

[@airconditioningrepairatlan2438]

Good video Thanks! , I learned something new!!!

[@grayfurnaceman]

+Air Conditioning Repair Atlanta Welcome GFM

[@chrisvis9]

Thank you! Saved me an expensive HVAC service call. Ended up having an earwig caught under the contactor as you described.

[@grayfurnaceman]

Glad I could help GFM

[@teddyle7820]

+grayfurnaceman should the contactor always closed?

[@grayfurnaceman]

Only when the unit is calling for cool. GFM

[@Kaibil66]

Thanks for the tips

[@COcraig75]

Great video! Thanks.

[@grayfurnaceman]

Welcome GFM

[@naeemmaqboolmaqboolmasih73]

can we touch 24 volt of the contactor and they are might be dc voltage.

[@corruptedbrain6]

side note: When you checked from L1 to T1 you had 240v only because your contactor was stuck Open BUT if the contactor was engaged and you checked from L1 to T1 you should receive 0 volts only cause its the same leg with no voltage drops confirming that switch is functional :) Just extra information.

[@grayfurnaceman]

Sounds like no power to the contactor coil. A voltmeter on a/c volts with probes on the low voltage terminals on the contactor should tell. If no 24 volts at the coil, the problem is in low voltage controls. Does indoor fan run?

[@danplays5556]

Hi it was helping Thank you

[@professorkiwi]

Good video. I encountered a failed contactor that was welded shut. Nothing I could do but replace it.

[@grayfurnaceman]

The 24v control voltage usually comes from the inside air handler. The 12v you are getting is probably a ghost voltage. You can jump from R to Y at the air handler to see if it works then. If so, the remove the stat and again jump from R to Y. If so, the stat has failed. Hope this helps. GFM

[@rolandvz71]

ok....starting to sink in--thx for the info! I will update my findings...

[@marconator3896]

nice job

[@mjshuja1948]

I watched your whole video 👍👍👍👍👍👍I HAD SAME PROBLEM IN MY CONTACTOR 😡😡😡😡MY AIR CONDITIONER KEEP RUNNING😡😡😡😡I HAD FROST ALL OVER MY UNIT😱😱😱😱😱😱I DID A LOT REACH 👍👍👍👍👍I TOOK OUT MY SINGLE POLE CONTACTOR👍👍👍👍REPLACED BY DOUBLE POLE👊👊👊👊👊✌️✌️✌️✌️👍👍👍

[@grayfurnaceman]

Ok. You have a refrigerant leak. The power is coming from the thermostat and when it comes to the board outside, the board looks at the low pressure switch, sees it is open and cuts power to the contactor. It is a safety switch to keep the unit from running if the refrigerant charge is too low. Look for oil slicks, especially around service valves. Hope this helps. GFM

[@jrr1016]

Great video. I understand the voltage across the open switch as it’s the difference of potential. If it was closed it would be millivolts or zero. I don’t understand the 240 across one side either. I would have expected 120 as well.

[@grayfurnaceman]

120 volts to ground or neutral and 240 volts from one line to the other. L1 120 volts, L2 120 volts. Add them together. GFM

[@jrr1016]

@@grayfurnaceman I gotcha. Single pole contactor vs a 2 pole contacted. The shunted side was what was screwing me up.

[@grayfurnaceman]

On most units the power comes from the thermostat to the outdoor unit. The board is not involved. If your indoor fan is on then the thermostat is calling. Assuming the color code of the stat wire is "normal", the yellow wire at the wire nuts at the outdoor unit should have power to common. If so and there is a board in outdoor unit, high or low pressure sw may be off due to charge problem. If not check yellow at furnace. GFM

[@genekerr8064]

Awesome! Thank you.

[@grayfurnaceman]

Welcome GFM

[@grayfurnaceman]

Sorry, your comment was in spam. That sounds like the fan is drawing too much power and the overload is kicking off. Did you replace like for like? You might also check to see if you wired it right. After it shuts off, check the motor for overheat. If you have an ammeter, clamp one of the fan wires (not the capacitor wire) and compare to the rating on the motor. Hope this helps. GFM

[@killerdungbeetle]

I just used your video to troubleshoot and fix my a/c unit...but I'm not sure what happened. As I was checking the voltage across the two input terminals, the fan and compressor magically turned on and now everything seems to be working fine. The contactor had been pulled in all morning, but the fan and compressor had been dormant. Any idea how simply checking the voltage started things back up? I've since turned the unit off and on, and it's still working fine.

[@TrevorBurrell1]

Iam Getting no power to the contacts in and out wat should I do next??

[@MsFishingdog]

great vid.

[@grayfurnaceman]

Thanks for the support. GFM

[@puma733]

I'm having an issue where I turn the ac on and it works for a few cycles but eventually when it kicks on the contactor doesnt kick on unless I manually push it in then it will work. I replaced the capacitor and contactor. Any suggestions

[@Jjiihhhgges]

quick question: is it possible to place another contactor with same rating in parellel with this contactor and add a transistor to amplify current and add a therimstor so that when original contactor heats up the spare contactor starts working and when it cools down the resistsnce of the thermistor decreases and the original contactor starts working? Thank you sir

[@imbroken73]

thanks for that info

[@grayfurnaceman]

Welcome GFM

[@dannymoreno03]

Excelente 👌👌

[@MrBollivar]

Best video I have ever seen on troubleshooting HVAC. I had high voltage come through my house caused by the electric cable being damaged for a storm. The central air stopped working. A tech came out to check the central air unit and told me I needed a new compressor. Both capacitors were shot and were replaced. There was no electricity coming out of the contractor back to the house (furnace). The tech didn't check the contactor. Any ideas?

[@laothakao]

What if you had 28V across the coil to ground. Both side to ground?

[@bob559ek]

ok no volts on the contactor 24 volt side and the indoor fan does run and i also checked the thrmostat and i get 24volts there i also notice that the ondoor fan never turns off do u think it could possibly be the control borad

[@BrettBMW1]

thank you

[@grayfurnaceman]

If you are concerned about the voltage being too high at the coil, 28 is not excessively high with these low voltage transformers. If you read 28 volts to ground, that is normal on one side of the coil. Virtually all low voltage t-formers are grounded on the common side. The common side should not read voltage to ground. If so, there may be a no chassis ground at the A/C. One side of high voltage to chassis should read 120v if ground is ok.

[@AmericanOutdoors1]

Thank you! Saved me a 300 dollar service call. I had burnt contacts.

[@grayfurnaceman]

Welcome GFM

[@Shadygrady1]

Excellent video thank you for sharing! 40$ for a new contactor and I am back in cold air :)

[@marksilliven5121]

Thank you

[@grayfurnaceman]

Welcome GFM

[@CharlesHaveoneakaInsanePatient]

I have a question? I have a Trane xl 1000 I replaced the capacitor and the fan motor, (( i thought the fan was bad it was about 17 yrs old ands was making a bad noise)) now the fan runs for about 3 minutes and shuts off and the compressor still runs. could this be a bad capacitor? or could it be the contactors?

[@ScottDLR]

Great video! Is there ever a concern with contact resistance building up in an old contactor?

[@grayfurnaceman]

Yes. If there is even a small resistance, the contacts will burn up. GFM

[@grayfurnaceman]

Generally, if the bar is not down, there is no control voltage. So look for a problem with thermostat etc. Hope it helps. GFM

[@grayfurnaceman]

If you are getting 240v on the power side of the contactor, but 0v on the compressor side, with the contactor pulled in, the problem is in the contactor. Could be a bug in the contactor contacts. I did a vid on this. It is in the contactors playlist. GFM

[@bob559ek]

ok when i push the contactor button in the a/c work find but as soon as i let if out it turns off help me out

[@hectorguerrero2582]

GREAT !!!! THANKS

[@rolandvz71]

OK here is my deal....w/the contractor energized L1 & L2 @ the bottom of contractor 120v to GND. @ the top of the contact w/it still energized 120v to GND, but phase to phase I get 0v on both top and bottom? So I think I have a problem w/my FLUKE....Soooo I checked the voltage @ the panel 120v to ground and 220v phase to phase. Fan and Compressor still not working.....need help getting hotter here in South East Texas!

[@eddiesepictouch]

OK when I turn unit on indoor blower comes on but compressor and fan not kicking on unless I manually push contactor.

[@grayfurnaceman]

+eddie z (eddiesepictouch) You could have problem with the wiring to the outdoor unit or a safety switch in the outdoor unit is open. Hope this helps. GFM

[@cabralboy91w]

Awesome video for a layman like me. Ended up spending $15 instead of $250. Of course though I know common sense of safety with electrical work as well.

[@grayfurnaceman]

Glad it helped. GFM

[@basilboolis7708]

hi Sir, Thanks for the great video !! at 2.22 time this is reading 240 volts across the two wires. I understand one side of contactor is supply 120 volts, but what about the other one across, where is it coming from or connected to ? and how come it has another 120 volts ??

[@grayfurnaceman]

This is difficult to answer in just a comment section. You will need an understanding of the 120-240 volt system. You can try my playlist: Electric in the panel grounding and bonding. GFM

[@bobbybenn8822]

thanks for video. I have one question, since I'm a novice. I had capacitor tested, by service personnel and it was bad, so was condenser fan. outside unit want come on until I depress button on contact. everything inside runs. should I replace contacts? it's a Tappan heat pump. thanks

[@grayfurnaceman]

You are not getting low voltage to the contactor. Check voltage to the coil of the contactor. Should read 24 volts. GFM

[@grayfurnaceman]

The air handler does not supply power to the outdoor unit. You are looking for 240v power to the outdoor unit. GFM

[@raymondpenton4342]

Question Dr. Z, I have an old electric Carrier unit that does not shut off unless I turn off the breaker and it also sometimes blows out cold air instead of heat, when it does that I shut off the breaker and it resets then blows out heat. Can you please tell me what wrong with this unit.

[@grayfurnaceman]

+Raymond Penton Sounds like flame failure. Have you cleaned the flame rod? GFM

[@2egenjerry]

Great video thanks! Question : my contactor bar is popped up and when I push it down, it'll start the AC unit but will not stay down when I let go. It doesn't look like I can remove or replace the bar. Does the whole contactor relay have to be replaced? Thanks!

[@grayfurnaceman]

The contactor is not energized. When there is a call for cool, the indoor fan is turned on and the outdoor contactor is energized. You need to find out if there is 24 volt power to the contactor. GFM

[@truckinforever985]

What about if the low pressure switch on the line off the compressor not allowing 24 volt to the contactor

[@truckinforever985]

H