DC Voltage Heat Relays for Electric Heat

I have gotten quite a few questions on heat relays lately. Especially DC voltage heat relays. Some people on KZbin have actually been talking about them as well
This video touches on the traditional AC voltage contactors and heat sequencers and also the DC voltage heat relays. We'll talk about how they work, how to check them for proper operation, and how I would replace one with a heat sequencer or contactor should I need to in the field.
00:00 Intro to Heat Relays
05:00 Why Use a DC voltage relay?
06:40 Resistance checks on relay coils
09:25 Inside of air handler unit

[@jamesmarcelin2216]

Thank you for showing the actual hands on part while explaining thoroughly. If I can see someone doing it, I can get to the point of repetition.

[@fighkb]

Thanks for sharing these videos, now I got a good understanding about how DCV relays works.

[@johnjennings487]

Too easy. Thanks for watching.

[@Rodny1231]

John these are excellent videos that you are putting out. Please continue to churn these out because in this line of work the learning never ends. As a former student of yours I can truthfully say that you are the best teacher, in my opinion, in the HVAC dept at FTCC.

[@johnjennings487]

I feel like I should get an Oscar or something now! Thanks. There is a lot to cover and I am hoping that with the videos some of the guys starting out will be able to keep the info in their head a little easier. Everybody watches KZbin right!?

[@scottallen5182]

Very informative as always!

[@johnjennings487]

Thanks.

[@samyz1660]

John rock it again with excellent video. Please keep it coming. I learned a lot. God bless you.

[@johnjennings487]

Thank you. God bless you too.

[@simmonsjr25]

Very nice info. Keep them coming.

[@johnjennings487]

It's almost time for the heating season so I have to keep you thinking...

[@MrEltinieblas]

Awesome! Excellent explanation John. I’m learning so much about relays, sequencers, and heat strips watching your videos. If you get a chance to do one on wiring a 15kw heat strip kit that would be much appreciated. Thanks!

[@johnjennings487]

Thanks. I will try but I don't think I have one in the shop right now. I'll keep it in mind.

[@sarge1189]

Excellent video. Thank you so much!

[@johnjennings487]

Thanks.

[@andybauer4363]

Thanks for your videos.

[@johnjennings487]

Thanks.

[@billmiller5075]

Very good information

[@johnjennings487]

Thank you.

[@uniontradeslive]

Great video!

[@johnjennings487]

Thanks

[@caseyjones3522]

yeah right. It's more "efficient" but I've seen plenty complaining about the Carrier ones failing.

[@johnjennings487]

Got a Trane unit on my house and it has just a plain contactor...never had an issue so its pretty efficient for me!

[@luisjose8380]

Thank you so much

[@johnjennings487]

Thank you.

[@broncheemims8493]

well explained

[@johnjennings487]

Thank you.

[@drg424]

John's right , the sequencer will also work , I've also got the same theory on older automobiles the cdi ignition was more reliable than the coil pack, again engineers trying to reinvent the wheel, auto, hvac, same if it ain't broke don't fix it, oh I drive older cars also rebuild them and drive um without worry .appliances ,auto , hvac imo engineers need to get lessons from old tech like john b 4 reinventing the wheel.

[@jpcooper78]

Big fan of how you save the plug for the DC relay when you put a sequencer or contactor in it’s place. Stealing that idea

[@johnjennings487]

Thanks. Can't put it back if you don't have it ..right!?!?

[@alk3r056]

Hello, do you know if the connector of the Purple and Orange cables are AC or DC? I want to know if it has a specific position as I can put it either way...My unit has the Orange on TP1 AND the Puple on TP2,, Thank you

[@johnjennings487]

It should be AC going into that DC relay. There is a rectifier either on the relay or built in, depending on which you have of course, that changes the AC into DC for the actual coil.

[@retroguardian4802]

Got me an old heat strip in my shop. No idea where it came from is used so I was gana swap out the limits switches and rewire it. Do a little retro fitting since it's not made for my unit. I know of some basic electrical theory so I'm familiar with what a rectifire is. I'm glad you explained that because I thought I needed to run dc to the relay. I never woulda have thought a rec was hiding in there. I don't like using old so wanted to buy all new relays but now I'm think of just buying a sequencer. I have 5 coils getting up to 83 amps. What would you recomend? Thanks for any advice!

[@johnjennings487]

Maybe to keep wiring simple I would try to get a packaged sequencer that could handle the 5 strips. It is already 24v, in one part, and everything would come on like 1-2-3. It would be a little easier than putting multiple contactors or such in the unit.

[@johnjennings487]

Depending on exactly how many strips you have you could look up something like a 5 switch sequencer. Plenty of name brands out there. Thanks for checking the video out and commenting.

[@retroguardian4802]

@@johnjennings487 Thanks. Exactly what I was thinking. I saw me one on ebay that can handle 5 coils for 20 bucks. I havent even looked to see if that was the cheapest yet. It was name brand. Not sure what I will do with all the extra room. Maybe install a cut out with a sighn. "Reach in here and guess what is inside." Used to play that game in school. Teacher would pass around a myster box with a hole in it. Very south of that would get a teacher locked up today probably lol.

[@johnjennings487]

Yeah. They would lock you up and then throw away the key!

[@alexvallejo1553]

Blower would run nonstop even with the Thermostat disconnected. Relay started beeping on continuity setting before I energized it. Bad relay? 😅

[@johnjennings487]

Sounds like a closed switch to me from where I am sitting! Blower running with the t'stat off the wall??? I would think that it has to be a switch closed in the high voltage side of the relay to make that happen.

[@timrogers961]

Did you find your problem with the blower running continually? I'm having the same problem with a Carrier heat pump after a lightning storm. Fan and heat strip running even with thermostat pulled from wall mount. Only cuts off with the breaker. Outdoor compressor and fan are off and don't respond to thermostat.

[@eomfd]

Hi John, I haven't been able to find any other videos that have those Warren relays which is exactly what I have. My fan won't shut off even with the thermostat removed, and a HVAC technician told me I need to replace my relay. Is he referring to these relays? Or would they not affect the fan since they're heat relays? I have a Carrier w/ ECM motor, interior of the air handler looks just like your video.

[@johnjennings487]

The ECM motors I've seen are not gonna usually hook to the heat relays like the older PSC motors do. Whether you have an X13 or a more "variable speed" motor likely wouldn't matter. Do you know the model of your air handler?

[@eomfd]

Yes it’s Carrier FX4DNF037

[@johnjennings487]

That unit seems to have the X13 blower motor. The way that motor gets is signal that the heat is on is by a low voltage white wire. If you look inside the air handler you should see a bunch of wires connected together...white, purple, blue (I think). And one of those wires goes to the blower motor. It dowsn't wire up like an older unit with the heat relay connecting back to the motor. If you removed the thermostat face and it still works the you would need to check for voltage going into the plug by the motor. If one of the low voltage wires (blue or white) have 24v on it then that is likely the reason the motor is running. If not then it could be the motor module that has failed and is keeping the motor on. I doubt is is anything with the heat side of things but you definitely need a electrical tester to get to the bottom of it.

[@eomfd]

@@johnjennings487 According to the schematics on the motor, the brown wire going to the plug is the 24v. When I test it with a multimeter, there's no voltage. When I pull out that brown wire from the transformer and test the tab, the tx tab itself does have 24v. But weird thing is, whether the thermostat is on or off, the brown wire still doesn't read any voltage at the motor plug.

[@eomfd]

@@johnjennings487 At the motor, I removed the blue wire that's fan speed setting and white that says heat. The fan is still running. So does that mean I have a faulty module?

[@drg424]

Done it myself , the old school relays worked just fine more reliable, the old school psc motors worked just fine,more reliable, the office piston nothing to break instead 0f txv , if it ain't broke don't fix it , the money saved by all this garbage just makes the customers cost go up on pre mature failure imo, the energy saved imo don't justify the extra expense of newer unreliable junk.