How an Air Handler & Heat Pump Work & are Controlled by 24v Thermostat Wires!

What is the model of this thermostat plz? Is it universal?

Thank You for the in depth explanation on this.

Man, I love your video!! I took HVAC for 2 years at my local college and they really did not explain it to me as well as u have in 19 minutes of your video, now, not saying they did not do a good job in teaching me but I feel like they only taught me the very minimal basics on HVAC. Very pleased with your video and I wish I could have had this training in school, thank you again!

What causes the pump to run with thermostat off

As far as safety goes, you should mention that the cap in the outdoor unit, that big silver one, can kill you. DON'T TOUCH! Even if off.

WOW again so impressed by your abilities to teach us very thoroughly🙏 thank u

Umm, why did you use blue in your wire to connect to the black on the condenser

Good show, after watching the show I thinking my reversing valve might not be working, I live on the west cost of Florida so it’s warm even at 3AM it might be 86 outside. My winter bill is about Twice the summer bill I be keeping an eye on it.

I am an electrical contractor. I have specialized in controls for many years now but I never worked in HVAC controls. Lately I have been installing home genetators and needed to know how the heat strips worked so I could interrupt them under certain conditions during generator power. I appreciate this thorough review of the split unit. I feel more confident now that I have had this overview. Thank you for posting.

Great video thankful for this video

Please

Make a video of a 2stage heat pump

can someone explain why the Yellow tstas wire being energize in. heat mode

Craig--excellent tutorial! I have almost exactly the setup you describe, air handler/gas furnace inside, and heat pump outside. I'm curious why the yellow compressor wire from TStat to Heat Pump (compressor on, whether reversing valve is activated or not for cold/hot) also needs to go to the air handler....presumably, increase fan speed when the heat pump is running? Does the heat pump require a faster circulating fan speed indoors than, say, emergency heat using just the white wire to the air handler heater?

Very thorough and clearly explained. I have a Lennox heat pump system that has not been able to run the heat pump. The defrost board Y terminal seems to pull the thermostat's 24v signal to ground, effectively shorting it out. I checked the defrost board for continuity to ground on Y with no wire attached and it seems to be shorted. Is this something you've seen? Seems like the Y input on the board should not act like a ground. This system is only a little over a year old, with no corrosion issues. I'm thinking either the board is bad or maybe a pressure switch is grounding the circuit.

Not sure if this comment will get replied too. But I have a question: When checking from the outdoor unit on a heat pump system, which wires do you test when in cooling mode. Is it red and yellow? Is it just yellow and ground? And when you test the wires, are you suppose to get a reading of 24v?

Denis thinks for the information

I live in the south Florida heat. How do I hack my Heat pump to stay in maximum cooling?

Great videos as always!! I have an older York heat pump system. I replaced the thermostat recently, when unit is calling for heat, the blower motor turns on, however the outdoor unit does not kick on. Is the outdoor unit supposed to turn on also, when calling for heat?

Appreciate for great explanation

i have normal 5 wires coming out of wall. why would air handler only have 3 wires (see 2 pictures of air handler above-wont let me attach:) and no wire on W heat terminals even though my heat worked fine when it was connected to honeywell thermostat…now changing to nest and heat is acting weird and smells gaseous for 5 min then heat turns off and stays off even though i have it set to a warmer temp. Any help greatly appreciated! can i send pics to you somehow? Single mom trying to get this working correctly while keeping my child dafe from fumes. I have the normal 5 wires coming into new thermostat but heating is not working properly like it was on older thermostat.

So with a system like this if the reversing valve went bad would the unit be incapable of switching from heating to cooling, or would that only cause the defrost switching to fail?

Just incredible. Thank you for making this video.

Thanks for your fantastic video and explanation.
R wire is going to the outdoor unit. Could you please tell me what the purpose of this R wire is? The new heat pump outdoor unit requires only 4 wires ( O, W, Y and C wires).
Thanks

Thank you so much for this video. Been working confident with heat pumps after this video but suddenly ran into a heat pump condenser that has w in and w out terminals. Have you had these defrost boards?

El mejor video que he visto.
Sería tan amable de hacerlo en español.

very good explanation of the basics of heat pump op

Soirry but you're explaining this like you're talking to someone who already knows all of this.

Question, my ptac unit stop working because of faulty control board, it is an old unit and can't find the parts anymore however I really don't want to throw away the rest of its components, (condenser, fans, compressor, etc,), so I am thinking about getting rid of the control board and replace it with regular switches like, wall thermostat, contactor, heat sequencer relay for the heat strips, do you think is a good idea or not? because I'm only concern about the safety switches in the control board, but by adding some pressure switches and heater limit switches I'm thinking it will be ok, besides it would be a fun project

Is it possible to run a heat pump with a straight cool air handler? AH only has common, 12V, fan. I couldn’t b/c during heat, I have R G W, no Y. Goodman 5 ton.

Edit: I think I just answered my own question. No (since I don’t know much) but I was just looking at my other AH that is designed for a heat pump, it has all the guts for sending Y compressor out. Mine don’t have all those wiring. My 4ton unit at work also has the same guts for a heat pump setup.

So I'm a building engineer and I was wondering if they make a reversing in valve with a hot gas bypass so you don't have to worry about switching back into cool mode just for defrost the condenser. Because I know our chillers have it at my work and it just uses it to put a load back on the chiller.

So I guess the reversing valve fails in heating mode from what you said. which sense makes because you wouldn't want it to fail in cooling mode and freeze your house out lol. Awesome video gained some massive knowledge on this.

What is the black wire at top of thermostat not connected?

All I can say is, you are awesome. Having thermostat issues. These videos are excellent!!! Thank you

This video is the coldest break down I've seen NBS!

so emergency heat is for when the heat pump is broken and you're only getting heat from the handler?

How come the manufacture of heat pumps don’t keep the blower motor 120v? Instead of the 240v?

You are in good company for not knowing when a carrier heat pump will go into defrost. If it worked like you said, the heat pump would be in defrost mode every thirty, sixty, or ninety minutes of heat pump runtime if the defrost tstat happened to be closed at the end of that time period.
How it actually works, is once the defrost tstat is closed, the timer starts. As long as the defrost tstat STAYS closed, the timing will continue. If, for example, the runtime with defrost tsat closed is forty minutes and jumper is set for sixty minutes, and defrost tstat opens at 65 degrees of coil temp, the timer resets to 0 minutes of runtime.
So, its how long the defrost tstat has been ENERGIZED that determines defrost. And that time resets if not met.

Love your videos sir.Invaluable for people learning online,thank you!

This would be great if I had all these wires but I only have 4 with a new heat pump

Woops thirty years later..I wondered why the heck would people put blue to common.

Impressively complete discussion! Thanks.

Very good

I am Muhammad naeem

The red wire from xfmr, goes to power the thermostat. But I noticed that, it also goes to the heat pump. Maybe I missed it, but what does the red wire do at the heat pump.

Hi Craig question, I had a Custumer the want to install a heat pump, but he want to feed the outside unit from the tenant panel for AC and from the house panel for heat in other words he pay for heat the tenants pay for AC, so it going to be be two feed for same unit is anyway to interlocking those two feed using a rely , any idea if it possible?

how do you hook up an heat pump type heater/cooling system to a system that only uses outside a/c unit with a heat strip only inside? thanks, Robert

Thank man that’s was great