Understanding Low Voltage Wiring for AC & Heat Pumps 3D

This 3D video shows how low voltage wiring works in a typical heat pump system. We cover schematics, some electrical circuit basics, how the low-voltage circuit accomplishes its tasks, and some best practices to maximize the longevity of your low-voltage circuits.

There will be three diagrams: the condenser, heat strips, and air handler each having its own schematics.

Those ac schematics show various types of switches, including basic switches, pressure switches, thermal switches, float switches, and contacts. An open switch has no electrical path, meaning that the equipment can't turn on. On the other hand, a closed switch allows electricity to pass through, so the equipment can turn on. Switches will be either in the normally closed or normally open position, and the schematics will indicate the normal state of the switch. It's also worth noting that switches are power-passing devices and do not use or consume electricity. In the condenser, you will see high and low-pressure switches. The heat relay on the heat strips will have a prominent pair of normally open contacts. The air handler usually has a normally closed float switch, which opens when water fills it up and breaks the circuit.

Compared to switches, loads are power-consuming devices that transform electrical energy into some other form of energy. The contactor coil and reversing valve solenoids are examples of loads.

Within the thermostat, G (green) goes to the blower, Y1 (yellow) is for the contactor, O/B (usually orange, sometimes dark blue) is for the reversing valve, RH (red) is for constant 24v heat (RC is constant 24v cool), C (blue) is for common, and W2 (white) is for auxiliary heat. In this case, we are using ACC+ (black) for dehumidification.

The transformer is the source of the 24v power that starts everything. Transformers take high voltage (often 230v) from the power company on the primary and drop it to 24v on the secondary, which then goes to the integrated circuit board. The primary and secondary interact electromagnetically; they don't actually touch.

When the 24v power makes it to the integrated circuit board via SEC1 or SEC2, it passes through the 5-amp fuse and powers the R terminal on the terminal block. Due to that configuration, many techs wire the float switch to break R. Breaking R will stop power to the thermostat and the defrost board at the condenser. (However, some techs may break Y instead.)

Y goes from the thermostat to the terminal block and then to the contactor coil. The contactor coil needs 24v to pull the contactor in and close the contacts that allow power to reach the compressor and the condenser fan. Y goes in and out of the high and low-pressure switches before reaching the contactor coil.

W2 connects to the heat strips and W on the defrost board from the terminal block. So, either the thermostat or the defrost board has the capability to bring on electric heat.

The G terminal supplies constant 24v power to the blower fan inside the air handler.

Common feeds from the common side of the transformer and goes to the thermostat to complete the circuit. It then provides 24v common to the defrost board, which also completes the circuit on that side of the unit. We need common in all cases because it provides a path back to the transformer; otherwise, the circuits would all be open and would not work.

The O terminal's wire passes through the terminal block from the thermostat. Then, the 24v power goes to the condenser to energize the reversing valve solenoid in cool mode. (Note: Ruud and Rheem systems energize the reversing valve solenoid in heat mode, and these may have dark blue instead of orange wires.)

When we use ACC+ for dehumidification, the blower will only reach full speed when the DH terminal is energized on the terminal block.

When stripping back the wire jacket, try to minimize nicks by making a small vertical cut and pulling the sheath back. Cut the sheath you've pulled back. Cut the tips of the conductors, as you may have nicked them. Make careful cuts to expose the bare conductors; you want them to be able to reach the terminal block or touch under the wire nut, but they shouldn't be exposed.

When routing wires or cables through cabinets or other areas where they might get cut, be sure to use proper grommets. Don't run wires over metal objects like the capacitor, as shorts may occur. When routing the wires in a spot where they might chafe, rub out, or otherwise suffer damage, use a conduit whenever possible to protect the wires. Also, use zip-ties to secure wires with a bunch of slack.

Short circuits happen when there is an undesigned path, and open circuits happen when the path is interrupted completely. Try to minimize both as much as possible.

[emeryhvac]

Excellent informative video. I hope anyone new or apprenticeship students watch this.

[Aiundergroundstudio]

The visual presentation is amazing. Honestly one of the best training videos I've ever seen

[ProjectAmoeba_]

As a new HVAC apprentice, this video has really helped me understand a great deal on how the system runs and what's required for system to operates properly

I'm a month in as an apprentice and have learned more things these last few weeks on the job than I did in 2 years at my last job ! Things are slowly starting to make more sense each day and these videos help a lot to further cement and expand on my experience in the field

[PCSxNTX]

Just started my apprentice ship at 31 have 8 years oilfield experience producing natural gas wells

Anyways I just started watching these videos to help better understand what I'm being taught on the job and let me tell you, learning at the pace at which a season veteran of the trade works can be challenging these videos help fill in the information gaps that get lost in transmission

[theadventuresofvm]

Wow you outdid yourself with this one. I’ve been watching your videos for years because it’s always such good information but the illustration with the video was absolutely amazing.

[connerkinsman]

Ive watched a lot of hvac help videos, but this one tops them all in terms of how easily understood and helpful it is. Great visuals, good commentary, clear and right to the point and very thorough. I wish they'd all be like this

[Rishnai]

Someone give that animation team a medal

[NatetheHouseWhisperer]

Wow. As a non technician myself I found this extremely helpful. A whole lot of mystery was lifted.

I particularly liked the white dot moving through the wires.

Remarkable explanation in a very short time. Well done!

[coldfingersub]

Videos like this must be recommended to every HVAC instructor and every college in trade school for their students.

I’m always constantly trying to convince automotive technicians who been in the business five or 10 years in drive ability in electrical who are thinking of changing trades to go over into HVAC or HVAC/R telling them they will get paid better the work is easier and the systems are so much simpler like working in the cars from the 1970s and 1980s.

[joes.]

Incredible, whoever did the animations deserves a raise.

[chrisduncan]

It drives me crazy to see people not using the pull string to strip the outer jacket of LV wires.

[joelsalmon]

Please 🙏 don't ever stop making these videos!

[noelv]

I’m working as an apartment maintenance technician and noticed these air handlers don’t have a circuit board. All these low voltage wires are wire nutted. Sucks that most of these videos don’t show this kind of example. But I get how it works thanks to these videos. Much appreciated 🙏

[josephconway]

When I went to school for hvac, there were many issues with that particular school. Besides the instructor not showing up regularly, when he didn't show up, they would "babysit" us with old, outdated early 1990's computer simulators. You're videos, especially this one, would've been HIGHLY Valuable for us during the first week which was all the time they dedicated to "basic" electricity. This video is WELL put together, straightforward, relatively easy to understand and follow, Pause able (which is Great!). I was in school in 2003, not 1973!! Unfortunately I didn't find your channel until several years after leaving the trade, but I still really appreciate the knowledge you impart through your videos!! Two Thumbs👍🏻👍🏻 WAY UP to HVAC school!! I am a proud subscriber, I watch all the videos, I like them all and I get notified of new ones!! Thank You SO MUCH for what you do!! On a side note. A bunch of ham and eggers in class would talk about once they got the epa certification (one of the few good things offered at the school) they would all head down to Florida (from Connecticut) because they "heard" you only need epa certification in Florida!

[arielmercado]

just sent this to some apprentices, wish i had this video when i was starting out.

[soloralphlauren]

Ive been doing this for almost 4 years at this point. My company never showed or taught anything like this so ive had to figure A LOT of stuff out by myself. Thank yall so much for the free lessons. It helps so much.

[musakavalci]

Credit to you and your team. Beautifully presented and can't wait for more of the same. 👌🏼👍🏼

[ParabellumX]

I just started going back to college (this time, for HVACR). I could watch your videos over and over again!

[jackwiser]

This is the kind of videos I’m looking for. I do commercial. I’m also still new at this. Love the simplicity of the way you teach in the video. Need more thanks

[chancefelling]

Outstanding from schematic to visual....