Klein Trade Program – Week 22
HVAC Trade Program Week 22: Mini Splits, Evaporators, Drains & HVAC Fundamentals
September 19, 2026
Week 22 of our free HVAC training program in Bunnell covered evaporators, drains and float switches, mini splits, and two things we’re going to keep coming back to over and over again: the refrigerant circuit and the low-voltage circuit.
We spent a lot of time on both of those last week.
This week, instead of me explaining them again, I had the students explain them to me.
That’s going to become a regular part of this class.
If you really understand something, you should be able to explain it.
HVAC Job Ready
This week’s HVAC Job Ready curriculum covered evaporators, condensate drains and float switches, ductless systems, and gas heat.
We don’t have a gas furnace in the shop, so we covered that through the curriculum and focused our hands-on time on the equipment we actually have in front of us.
We also carried some of the evaporator, drain and float-switch material over from last week because we didn’t get to spend as much time on it as I wanted.
I’m not really concerned with staying perfectly on schedule just so we can say we covered something.
I’d rather slow down and make sure everyone understands it.
Explain the Refrigerant Circuit to Me
Last week, we spent a lot of time following the refrigerant circuit.
This week, I turned it around.
Explain it to me.
Start at the compressor.
Where does the refrigerant go next?
What’s happening to the refrigerant in the condenser?
Where does it go after that?
What happens at the metering device?
What’s happening inside the evaporator?
And then where does it go?
Compressor → condenser → metering device → evaporator → back to the compressor.
But I don’t just want them to memorize that order.
I want them to understand what’s actually happening.
Where are we absorbing heat?
Where are we rejecting heat?
What’s happening to the pressure and temperature of the refrigerant?
Why?
If you’re going to diagnose air-conditioning systems, this is foundational.
We’re going to keep coming back to it until explaining the refrigerant circuit is second nature.
Now Explain the Low-Voltage Circuit
Then we did the same thing with the low-voltage circuit.
Explain it to me.
Where does our 24 volts come from?
What happens when the thermostat makes a call?
Where does the voltage go?
What components and safeties are in that circuit?
What happens if a float switch opens?
What happens at the contactor?
Again, I don’t want them memorizing a diagram.
I want them to be able to look at a system and follow what’s actually happening.
Because eventually the question isn’t going to be:
“Can you explain the low-voltage circuit?”
It’s going to be:
“This isn’t running. Why?”
And if they understand the circuit, they don’t have to guess.
They can follow it.
Evaporators, Drains and Floats
We spent more time on evaporators, condensate drains and float switches this week.
Here in Florida, removing humidity is a huge part of what an air conditioner is doing. All of that water coming off the evaporator has to go somewhere.
We talked about the drain pan, primary drain, traps, float switches and what happens when a drain backs up.
This also ties directly back into the low-voltage circuit.
A customer might tell you:
“My outside unit isn’t running.”
That doesn’t automatically mean there’s something wrong with the outside unit.
Maybe a float switch opened because the drain backed up.
If you understand the control circuit, you can figure that out pretty quickly.
If you don’t, you can spend a lot of time looking at the wrong thing.
Mini Splits
The other big topic this week was mini splits.
I have kind of a love/hate relationship with mini splits.
They’re really good equipment for the right application. They’re efficient, quiet and they solve some problems that are difficult to solve with conventional equipment.
They’re also way more complicated than most customers realize.
We actually have an entire A/C University article called Mini Splits Suck: A Letter From Your HVAC Technician that explains some of this.
The title is obviously a little tongue-in-cheek.
Mini splits don’t suck.
Working on them sometimes does.
“I Saw One at Costco for $365”
This is part of the problem with how mini splits are perceived.
Someone sees one at Costco or online for $365 and understandably thinks:
“How can it cost thousands of dollars to install one of these?”
Because the $365 box is only one part of the job.
There’s electrical work.
Refrigerant piping.
Drainage.
Mounting.
Wall penetrations.
Pressure testing.
Evacuation.
Commissioning.
Permitting and code requirements.
And then there’s actually knowing how to work on the thing when it doesn’t work.
That’s where mini splits get interesting.
Depending on the equipment, you may have an inverter-driven compressor, electronic expansion valve, thermistors all over the place, communication wiring and proprietary control boards.
There’s a lot happening inside that little $365 air conditioner.
That’s something I wanted the students to understand.
The cost of the equipment and the complexity of the equipment aren’t necessarily the same thing.
We’re Putting One in the Classroom
We’re also going to install a mini split in the shop specifically for training.
Yes, it’ll cool the classroom.
But that’s really not why we’re putting it there.
I want the students to have an operating ductless system that we can actually use.
We can take it apart.
Clean it.
Follow the refrigerant circuit.
Follow the electrical and communication circuits.
Look at the drain.
Take readings.
Create problems.
Troubleshoot it.
And put it back together.
That’s how I want this program to work whenever possible.
Reading about something is good.
Seeing it is better.
Actually working on it is where things start making sense.
It’s Still an Air Conditioner
This was probably the biggest point I wanted everyone to understand about mini splits.
They look different.
The electronics can be very different.
The controls can be different.
But underneath all of that, we’re still moving heat.
There’s still a compressor.
There’s still a condenser.
There’s still a metering device.
There’s still an evaporator.
There’s still airflow.
There’s still condensate.
That’s why understanding the fundamentals matters so much.
If you understand why an air-conditioning system works, learning different equipment becomes a lot easier.
If you’ve just memorized how one particular machine works, you’re going to struggle every time somebody puts something different in front of you.
What’s Next
We’re getting to the point in the program where I want to start putting more of these individual lessons together.
Instead of asking:
“What does this component do?”
We’re going to start asking:
“The system isn’t working. Why?”
Then the students are going to have to follow the electrical circuit, refrigeration circuit, airflow and safeties and figure it out.
No guessing.
Prove it.
That’s where we’re headed.
The Klein Cooling Free HVAC Training Program is a community-based HVAC trade program in Bunnell, Florida.
We’re trying to give people an opportunity to learn the trade through classroom instruction, hands-on training, industry certifications and real-world troubleshooting without charging them tuition.
No tuition. No sales pitch. Just an opportunity to learn a trade.