A Blower and Heat Strip Dangerous Mistake

Bryan shows how not to make a dangerous mistake when using a relay to create a blower and heat strip interlock.
When heat strips run on a heat pump system, we want the blower to run as well. A G call controls the blower, and a W or W2 call usually brings on the heat strips. So, we want the G call to happen during a W or W2 call but NOT the other way around; a blower relay is not rated to handle the current of the heat strips, and we don't want to run the heat strips when we simply don't need to bring them on.
Stack sequencers, on the other hand, can typically handle the current of the heat strips.
To create an interlock, you will need a relay. There may be specific blower relays, but a 90-370 or 90-340 relay will suffice. It's best to think of the 90-340 relay as being upside-down when you're interlocking the blower and heat strips. In the case of the 90-340, we would connect L1 to point (contact) 3 or 6, heat strips to point 2 or 5, and the blower to point 1 or 4. In the case of a Carrier relay, we would connect the blower to common, normally open to the power supply, and normally closed to the heat strips.
When power goes through the heat strips in the event of a W call, it enters through the contactor from L1 and goes through the fusible links, goes through the heat strips, comes out through the other side, passes through the thermal limits, goes to the L2 side, and goes back to the power supply on the other side.
When we attempt to use a relay to interlock the blower, we might be tempted to attach L1 to common. However, if we connect the heat strips to the normally closed contact, it will either run all the time, cause a dead short, or not run at all. Therefore, reading the relay from left to right isn't useful. If we turn the relay upside-down, however, the new left-to-right orientation is really right to left. We'd connect the blower to common, and L1 would connect to the normally open contact.
If the W call forces the heat strips to come on, the power will feed through the normally closed contact to the blower. However, if we just get a G call, the relay coil will be energized, which will close the contacts between L1 and the blower to bring on the blower; it will open the normally closed contacts to the heat strips, so the power won't backfeed to the heat strips.
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[@MrChipBryant]

Thank you for sharing your knowledge!

[@vinnymac8127]

Perfect time to make this video, Bryan! I live in NC and much like you I mostly work on air handlers and this is all I've been dealing with since this little 2 day cold spell. Thanks for refreshing my memory!

[@dustyanderson8905]

Really appreciate the knowledge you share! Currently in school, your videos and podcasts have helped immensely. Thanks again!

[@acrraideredward9773]

Always had some doubt on those relays. Thanks for the advice!

[@hvacjohnnie]

🤯The simple things like that are the most looked over and most valuable things to learn in this field of work. Thanks for sharing.

[@bhagiraths]

Bryan, thanks for sharing the heat strip and its components in depth know how. You explained everything about interlocking blower and heat strip relays in such a good way. I am so happy to watch your videos. 👏👏

[@bikerbobcat]

So helpful! Working in HVAC really got me to understand logic circuits and puzzles more. I've never even considered "backwards" relays, just the activating terminals and the NC/NO working terminals.

[@awesomeaustin2348]

I learned this the hard way back in the day, thanks for sharing.

[@jeffgrizzel9499]

I’ve always had trouble remembering how this system wires. Thinking in terms of turning the relay upside down is a perfect way to remember it. Great idea. Thanks.

[@dustpan2000]

He should have worded it differently than "turning it upside-down"

[@LatinTurkNYC]

Never looked at it that way. It works when only calling for Heat, it works calling for only fan and it works calling for fan and heat together from the thermostat. I always looked at the relay in one way. Great video!

[@pblack.]

Yeah, this is a great operation

[@y4kv]

What would be the benefit or drawback to interlocking the heating strips with something sensing the airflow directly (ie sail or static pressure)? Clogged filters or broken belts aren’t accounted for by the fan motor power. Even a locked rotor may allow the heat coils to be energized enough to be damaged.

[@lilpbass]

Thanks this is my first heating season and I can use this information.

[@rafaelcastro6466]

Wow thank you, much appreciated! Great explanation!

[@jacobframe8769]

Great video and information, thank you for sharing!

[@ctorres441]

Great explanation , thanks for share knowledges with us

[@cedarhedgeprojects]

Loved the video. Too bad I didn't see it until after I smoked a relay and transformer and had a visit from the fire department. 😀

[@Barracuda48082]

In essence, the motor has the choice of power sources, from heater at terminal 2 or active relay term 3. Will be passing this on to the apprentices.. thanks Bryan. I will pass your name on to friends in SoFla. 👍🏼

[@HVACS]

Thanks Gary

[@robertsneed7689]

Wow, thank you very much. I was confused couple of days ago because I wasn't getting power to the fan motor. I saw the relays burnt underneath on the heat strip. Also my condenser wouldn't come on and I wasn't getting 24 volts to the thermostat nor to the contactor on low power.

[@TheAbdallah89]

thanks for the nice explanation

[@JoseGuerrero-sj5ie]

Great video sr good information about rally

[@JGlife891]

I don't know anything about this, but this is the most informational and straight forward video on this. My heat just went out. The same unit. I checked the inside and a red wire was unplugged from the fusible links. I wonder if that has anything to do with it not working now. It powers on but no heat no aux heat and a burn smell.

[@roberthaggerty5720]

A really good explanation thank you

[@roberthaggerty5720]

16 minutes of knowledge thx.

[@ryanbender8154]

I’m actually in this Predicament right now actually do u get rid of then the fan relay Bc this relay does both correct ???

[@donnahazelip9347]

very good,well done you

[@soneeeee4440]

good vid. need some help, i'm up north, first freezing cold day today since the winter, -13c. So my heat pump is off, aux heat strips took over in the air handler. It is a Trane 4tee3f37b1000aa, system about 12 years old. Noticed when the aux heat starts, there's a machine gun rapid fire/chatter sound at the air handler, right about where the red 20KW line comes in. i'm not really familiar with relays but could it be relays that turn the strips on and off?? (sounds like a machine gun, fairly loud if i put my ear on the panel). Once the heat gets going and the fan is up to speed, it seems to stop, and then starts again a bit when the heat cycle shuts off. I'm still getting aux heat but not sure if the 4 strips are all working 100%. if i lost a strip or 2 out of 4 would the others continue to work or would they all stop?, Is there a fire hazard if either a strip is burnt or relay coils chattering furiously. Or could this noise be something else like arcing at the strips? the system cycles on and off a lot when it's too cold for the heat pump, nothing new but i guess that's normal, since the air is hotter, it gets back to temp fast compared to heat pump. If its a relay, how long can it function like this? is failure imminent? i am diy, have diagnosed and fixed blower motor module before and other basics like outdoor cap.

[@saltrue1555]

That was very instructive thank you very much for your teaching.God bless

[@jsteislures5361]

What type of wire should I be using between sequencer and coil?

[@Parabellum-X]

Brian, I am in HVACR school right now, and we have just started learning about Heating Systems. I was watching your video here, and, at 9:25, you said that (on a sequencer) between terminals 1 & 3 is Normally Closed, and between terminals 1 & 2 is Normally Open. However, the symbols on the side of the sequencer show the opposite! I am seeing a NO symbol between 1 & 3, and a NC symbol between 1 & 2! Was that a slight mistake on your part? Are they actually the other way around, or is that correct? I'm so confused! Thanks!

[@natepeterson7145]

Thanks sir 👍

[@kenbloker8429]

I don’t see how the heat strips would back feed through an open contactor but I understand what you’re saying.

[@jenko701]

Excellent

[@rj.parker]

As Ed McMahon, Johnny Carson's sidekick might say.... Bryan Orr, in a "... borderline divine and mystical way, will ascertain the answers having never before seen the questions" techs have always asked...

[@drg424]

Got a call about this same thing, easy repair, moral ,think it through before proceeding.

[@jimmynguyen2981]

Your videos are awesome ! Come to Dallas brother a lot of dull apples that could use some polishing as well as my self I’m 3 years in and eager to learn but, only the right way! I’m sure my employers who recently was named 2021 best medium size company to work for in Texas would welcome you to host a forum at our amazing facility...

[@helobeast]

Whats the model of that heat strip you have on display?

[@macster1457]

I just had the blower relay replaced with a 90-340 2-pole. Is it normal for it to make a loud click every time the blower kicks on?

[@renecuevas4128]

Tnk u Brian

[@mafosa8519]

... yea that was pretty cool!

[@user-hx5vh9uh2n]

What are heat strips used for?

[@samsonandarige396]

where the source of common come from ? I see 0nly L1 and L2 . the way i see you start the common from the fan through the contactor to L1 thanks

[@hvac01453]

Most relays I see are used to separate the high speed for cooling from the low speed for heat. If power were to feed both taps at the same time, smoke...

[@topher8634]

I always associate the common terminals with the common action. In this case we want the blower to run whether there is a G call or a W/aux call with G missing.

[@anthonybernier9952]

So just to make sure I understand we can NOT use that relay that’s not rated enough for the heat strips at all?

[@JP-sd2cw]

I can’t seam to grasp 6:18, L1 goes on your normally open, heat strip interlock is on normally closed and blower is on common, but idk how its being controlled if your common is hooked up to the blower?

[@HIMI2003]

What if the element glows half way through. Like some parts are low glowing red and some part aren't. (This is one big element

[@user-on1of7sg1i]

How to check voltage feedings a relay

[@-JonnyBoy-]

I had a sequencer go bad in an electric furnace in one of my rentals. I went to fix it as they said the fan comes on but no heat. The sequencer was defiantly bad but it was also wired up wrong as in it would never have worked that way ever. Tenant must have messed with it before calling me lol and it took me an extra hour to trace the wiring diagram to figure out all the correct connections. (i'm not a furnace repair may by any stretch so that was fun)

[@mikeh8047]

wont high voltage still be running through the relay when heat strip is connected to "2" through NC to "1"?

[@sajjadawan8691]

Not at all because you're not getting L1 ,means there is no potential difference so no current flow

[@brianmutascio8325]

How do you keep the heat strips from energizing , if the blower motor were to fail...

[@WreckingCr3W2]

Limit switches

[@wildman8601]

You need to zoom in on the board when you're writing stuff on it so we can see better

[@rodolfoplasencia9739]

Notice the conection of the relay up to 12:02 minute and see if is not the same as he said is to be done on minute 13:08? Shouldn't in both connections, drawn by him, connect the normally open and disconect the normally closed? Who assigned 9739 to my name? I guess am understanding that, if the relay on normally closed NC gets opened when connected and on normally opened NO gets closed when connected or powered, on the second connection up to 13:08 heater strips get connected via L1 closed connection on top left (not drawn closed but opened) conection between 2 and heat strips NC will open and get disconnected, and connection between 3 to 1 NO will get closed, am I right and the tech forgot to close the connection between L1 and heat strips because I've seen them always powered waiting to be closed.

[@Planet_Shel]

I have replaced a thermostat a blower circuit board and the heat pump circuit board how do I replace a blower relay? So the dang fan listens to the thermostat?

[@edilsonserafim4784]

1,2 NC 1,3 NO correct? thank you

[@thisguybri311]

Ok, Now I am confused... At 9:25 you say terminals 1 and 3 are normally closed and terminals 1 and 2 are normally open. Did I miss something or are 1 and 3 normally closed because we are reading right to left instead of left to right. I would think direction would not make a difference. Normally open is always normally open no matter what direction. Relays always confuse me😖😖😖 The symbols show normally closed between 1 and 2 and normally open between 1 and 3.

[@Domino8619]

You are correct. I think he mispoke.

[@timesfly1081]

Yeah I was taught that the term “normally” in normally open/closed refers to the state the switch will be in when you buy it off the shelf before any power it applied to its coil.

[@metal2444]

2 gain 2nd blower tap for cooling use 4 ---- 6 normally open.First on last off!

[@realSamAndrew]

9:24, you got it reversed for which contacts are NO or NC.

[@hvac01453]

I have seen this in the field “but”.... what you indicate isn’t true, if L1 feeds the motor and the heat strip (L1)when not calling for heat, the h3aters can’t come on because it only has one side of line, (L1) because it’s a two pole contractor, it has no L2 path on the heater side. Now, some manufacturers like Trane will direct feed one side, mainly on three phase. If you drew in a one pole contractor which is common nowadays, some call them a one and a half pole... your theory would stand.

[@HVACS]

True, the two pole contactor example isn’t the best

[@michaelcostello6991]

Thanks. Lucky i read this post before commenting. If both relay coils were powered the heater would/could get its amps from both contactors and the fan contactor might draw too much current if its resistance path was less than the heating contactor. Just a suggestion. ie you would have 2 parallel paths supplying the heaters. So the video is correct for safety reasons to prevent this happening or the possibility of it happening. Im not an electrician and this is just my take on it.

[@timesfly1081]

@@johndemarcojr3212 My thoughts exactly. Those single pole contactors are shockingly bad 😉

[@helloh984]

I was going to comment the same thing. I hope you can add a little note or edit to fix that mistake on the video. Btw i really appreciate your chanel.

[@williamdowling203]

This guy definitely knows how to be a good technician, but being a teacher is a whole different skill lol his classes very much seem like they would weed out the dumb and slow lol

[@pl747]

there is no time delay when the heat strips shut down to allow them to cool off.

[@nsboost]

Still lost 😅. God I’m glad their isn’t many heat pumps or electric AHU here. I have to rewards this when my son isn’t using me as a jungle gym

[@AgentOffice]

Heat pumps are becoming more popular now

[@timesfly1081]

That’s all we have here in Florida. Heat pumps on zone boards

[@nsboost]

@@AgentOffice it gets -20*F here and natural gas is cheaper than electricity. I don’t see them getting popular here

[@AgentOffice]

@@nsboost natural gas is starting to get banned in new construction

[@nsboost]

@@AgentOffice lol not here. Gunna ban natural gas when all our power in this state is provided by COAL!?! Please. You think the State Penitentiary, jails, colleges, hospitals here are gunna run their steam boilers (the size of 2 city buses) on electricity? 😂 😂 These are “Rules for thee but not for me”. People need to wake up. You shouldn’t be driving a petrol fuel car while those pushing that narrative fly around burning thousands of gallons of jet fuel. Their multi million dollar houses heated with top of the line natural gas boilers. Killing industries and killing jobs. Crashing the economy. Politicians inside trading. America needs to wake the hell up.

[@abelurrutia1192]

Normally closed from 1 to 3 and normally open from 1 to 2? It’s’ not that backwards?

[@timesfly1081]

lol yep he’s wrong on that one. You’re not crazy don’t worry 😂 1 & 3 = NO 1 & 2 = NC

[@Bluecollarrebel]

🤟

[@officerkrupke4966]

Your drawing on the board was confusing because you put an extra set of contacts on the other side of heater element. The Carrier diagram showed two sets of contacts because there were two elements, as opposed to your drawing with one element with two normally open contacts on either side.

[@shank0]

What if you put it up side right, but on the other side of the blower? Lol.

[@geraldschilli8870]

Another identifier on those type of (small black) relays is that the coil connections are externally soldered.

[@clevc112]

At 9:25 you say the NC and NO backwards.

[@Azemeraw.Electro-Mechanical]

Ok

[@user-hx5vh9uh2n]

I’m lost on this one. Have no experience on this topic

[@timesfly1081]

9:22 🙃

[@mk-vt2xw]

am i the only one who noticed at 9.28 the normally open, normally closed are wrong?

[@timesfly1081]

I ran to the comments so fast to find this comment at 9:22 🤣

[@patrickhutchins6935]

Do you have George Costanza's wallet in your front left pocket?

[@xephael3485]

These relays suck and are very expensive. I replace a type 91 with a 20a contactor. Furnaces have proprietary garbage for electronics.

[@knockitofff]

9:24 Even the teacher gets it wrong at times kids, actually it's the exact opposite of what he's saying here.

[@deathrawphantasma]

Thank you I was going crazy reviewing my old notes. I was wait what ! Lol

[@renecuevas4128]

In Energized position he is 100 percent right. But unfortunately yes cause always systems are shown in De Energized position Diagram s Wise😁

[@deathrawphantasma]

@@renecuevas4128 yeah you’re right

[@timesfly1081]

@@renecuevas4128 well energized or not, normally closed means not energized. When you buy it off the shelf it’s in its normal position which is open not closed 🙃 I was actually relieved to see that even instructors can make a mistake from time to time.

[@robertmoses2367]

Talks too dam fast. Not a good teacher 2:37

[@Stuart68505]

This was helpful. It might help to show the low-voltage wiring to the relay coils in another diagram as well.