Klein Trade Program — Week 5
Electrical Troubleshooting: Here’s the Parts. Make the Fan Run.
Saturday, May 9, 2026
HVAC Theory Certificate Program — Electrical Troubleshooting
Welcome to Week 5 of the Klein Trade Program.
Last week we introduced multimeters and wiring.
We talked about voltage.
Resistance.
Continuity.
Current.
Wiring diagrams.
And most importantly:
What does the number actually mean?
This week we took the next step.
Instead of looking at a circuit somebody else built, we gave the students the components.
We drew the wiring diagram.
Split everybody into two teams.
And essentially said:
Here’s the stuff. Make the fan run.
😂
Welcome to electrical troubleshooting.
This Week: Build the Circuit
Our lab started with a pretty simple goal.
We wanted a fan motor to turn on and off using a thermostat.
That’s it.
But to make that happen, the students had to understand how several components worked together.
We used:
- A disconnect switch
- 240-volt power
- A 240V-to-24V transformer
- A thermostat
- A float switch
- A capacitor
- A fan motor
- Wiring
- And a wiring diagram
Individually, none of this is particularly complicated.
Put it all together?
Now you’ve got a system.
And that’s where the learning happens.
Start at the Beginning: The Disconnect
We started with the disconnect.
Power has to come from somewhere.
In our training circuit, we began with 240-volt line voltage.
This gave us a perfect opportunity to reinforce something from Week 4:
Don’t just look at a wire and say:
“There’s power there.”
What voltage?
Measured between what two points?
Where does it go next?
What component is it feeding?
Follow the circuit.
That’s the habit we’re trying to build.
240 Volts Goes In. 24 Volts Comes Out.
Next came the transformer.
This was an important concept.
The equipment operates with different voltage levels for different purposes.
We had 240 volts available on the line-voltage side.
But our thermostat and control circuit operate at approximately 24 volts AC.
So we need a transformer.
At the beginner level, the idea is simple:
240V in. 24V out.
Now we’ve got control voltage.
And suddenly something they saw on a wiring diagram last week has a physical component sitting in front of them.
That’s when theory starts connecting to reality.
Now We Need a Thermostat
The thermostat isn’t magically “making cold air.”
It’s a control.
For our lab, we needed it to help control whether our fan operated.
That means the students had to figure out:
Where does the thermostat get its 24 volts?
Which thermostat terminals are we using?
What happens when there’s a call?
Where does the control voltage go next?
Now we’re not memorizing:
R means this.
G means this.
We’re asking:
What is actually happening electrically when the thermostat makes a call?
That’s a much better way to learn it.
Don’t Forget the Float Switch
We also put a float switch into the circuit.
Why?
Because this is residential HVAC.
And eventually a drain is going to back up.
😂
A float switch isn’t just some random accessory attached to an air handler.
It’s part of the control circuit.
Depending on how it’s wired and what it’s intended to interrupt, an open float switch can prevent equipment from operating.
So now our students had another component to think about.
The thermostat can be calling.
The transformer can be producing 24 volts.
Everything can appear ready to go.
But if the control circuit is open somewhere?
The fan isn’t running.
Now we’re troubleshooting.
And Then There’s the Capacitor
Our fan motor also needed its capacitor.
This gave us another chance to connect something we’ve been talking about to an actual working circuit.
The capacitor isn’t there because HVAC manufacturers had an extra part lying around.
😂
It has a job.
The motor is designed to operate with the proper capacitor.
Now the students are beginning to see that electrical components aren’t random pieces scattered around the equipment.
Each one is there for a reason.
Draw It Before You Build It
Before we started connecting wires, we made a wiring diagram.
This was important.
Last week, wiring diagrams looked like something a manufacturer created specifically to ruin your afternoon.
Now?
We’re making one ourselves.
That’s a completely different experience.
We know what components we have.
We know what we’re trying to accomplish.
So:
Where does power enter?
Where does it go?
Where does the transformer connect?
How does the 24-volt control circuit work?
Where does the thermostat go?
Where does the float switch belong?
How does the motor connect?
Where does the capacitor fit into the motor circuit?
When you build the diagram yourself, all those mysterious lines start having a purpose.
Two Teams. Same Problem.
Then we split the class into two teams.
Each team got the components.
Each team had the wiring diagram.
Each team had the same goal:
Make the fan run.
And this is where it gets fun.
Because now I don’t want to immediately tell you what to do.
Look at the diagram.
Talk to your team.
Follow the circuit.
Make a connection.
Check your work.
Ask each other questions.
If it doesn’t work?
Good.
Figure out why.
That’s the lab.
The Best Part Is When It Doesn’t Work
Seriously.
If you wire the entire thing perfectly on the first attempt and the fan immediately runs?
Awesome.
But we probably learned more when it didn’t.
Because now we have a question:
Why isn’t the fan running?
And instead of guessing, we have a process.
Do we have incoming power?
Do we have voltage at the transformer primary?
Do we have approximately 24 volts on the secondary?
Is the thermostat calling?
Is the control circuit complete?
Is the float switch closed?
Does the motor have the power it needs?
Is the capacitor connected correctly?
Where did we lose what we expected to have?
Now the multimeter from Week 4 isn’t just a tool we practiced using.
We have a reason to use it.
That’s the difference.
Stop Guessing. Follow the Circuit.
This is one of the biggest habits we want these students to develop.
When something doesn’t work:
Don’t start replacing things.
Don’t stare at it.
Don’t start moving wires around hoping something happens.
And please don’t immediately say:
“Probably the capacitor.”
😂
Follow the circuit.
What should be happening?
What is actually happening?
Where do those two things stop matching?
That’s troubleshooting.
The answer is somewhere in the system.
Your job is to find it.
The Wiring Diagram Is Starting to Make Sense
Remember last week?
Lines.
Symbols.
Numbers.
Components everywhere.
What the hell is this?
Now we’re looking at a diagram that we made.
And every line represents an actual wire the students need to install.
That’s powerful.
Because the diagram stops being abstract.
This line?
That’s this wire.
This symbol?
That’s this transformer sitting on the table.
This switch?
That’s the float switch in your hand.
This motor?
That’s the thing we’re trying to make turn.
Now the picture means something.
240 Volts and 24 Volts Are Doing Different Jobs
This lab also helped reinforce the difference between line voltage and control voltage.
The 240-volt circuit provides power for the equipment.
The transformer steps that voltage down for our 24-volt control circuit.
The thermostat and float switch become part of deciding whether that control circuit is complete.
And ultimately, all of those pieces work together to control equipment operation.
For a brand-new student, that’s a big step.
Last month:
“That’s an air conditioner.”
Now:
“Okay, the transformer has line voltage coming in and gives us 24 volts for the control circuit…”
We’re getting somewhere.
Hands-On: Make It Work
This is exactly why we have equipment in the shop.
It’s one thing for me to stand in front of the class and explain:
Transformer.
Thermostat.
Float switch.
Capacitor.
Motor.
It’s another thing entirely to hand you all five and say:
Connect them.
Now you have to think.
Now you have to communicate.
Now you have to read the diagram.
Now you have to physically make the connections.
And when the fan finally starts spinning?
BOOM.
😂
You built a working electrical circuit.
That’s a pretty cool moment when a few weeks ago you barely knew what any of these components were.
Stuff That Isn’t in the Manual
Talk to Each Other
There’s another reason we divided everybody into teams.
HVAC isn’t always a solo activity.
You’re going to work with other technicians.
Installers.
Helpers.
Apprentices.
Electricians.
Plumbers.
Inspectors.
Customers.
You need to be able to communicate.
If your teammate says:
“I think this wire goes here.”
Don’t just connect it.
Ask:
Why?
Show me on the diagram.
What should happen if we connect it there?
Working together doesn’t mean one person does everything while the other person watches.
Talk through the problem.
That’s part of the training too.
Stuff That Isn’t in the Manual
“I Don’t Know” Is Still a Perfectly Good Answer
We said this last week.
We’ll probably say it another hundred times.
If you don’t know:
Say you don’t know.
That’s especially important with electrical work.
Guessing confidently isn’t a skill.
If you’re not sure why a wire goes somewhere, stop.
Look at the diagram.
Ask your teammate.
Ask the instructor.
Trace the circuit.
Figure it out.
We can teach:
“I don’t know.”
It’s much harder to teach somebody who’s pretending they do.
And Don’t Just Copy the Other Team
😂
You have your own wiring diagram.
You have your own components.
You have your own meter.
The other team’s fan started running?
Great.
That doesn’t mean you should immediately start looking across the room trying to see where they put the blue wire.
Figure out your circuit.
Because eventually there won’t be another team ten feet away.
There will just be you.
A customer’s air conditioner.
A wiring diagram.
And somebody asking:
“So… do you know what’s wrong with it?”
That’s what we’re preparing for.
When the Fan Runs, You’re Not Done
This is another good habit to start early.
Getting the equipment to operate isn’t always the end of the job.
Understand why it operates.
Can you explain the circuit?
Can you point to the line-voltage side?
Can you identify the control-voltage side?
Can you explain what the transformer is doing?
Can you explain what happens at the thermostat?
What happens if the float switch opens?
What role does the capacitor play?
If I remove a wire, can you predict what happens?
That’s understanding.
We don’t just want the fan to run.
We want you to know why it runs.
What Should a Student Know After Week 5?
We’re not expecting anybody to diagnose every electrical failure after one lab.
We’re building skills.
By the end of Week 5, students should be more comfortable with:
- Following a basic electrical circuit
- Distinguishing between 240-volt line voltage and 24-volt control voltage
- Understanding the basic purpose of a transformer
- Understanding the thermostat as part of a control circuit
- Understanding how a float switch can interrupt equipment operation
- Understanding the capacitor’s relationship to the motor
- Reading a basic wiring diagram
- Turning a wiring diagram into physical connections
- Using a multimeter with a purpose
- Troubleshooting a circuit logically instead of guessing
- Working through an electrical problem as a team
- Explaining why a circuit works instead of simply celebrating that it works
Most importantly:
We started with a pile of components.
And ended with a running fan.
That’s progress.
This Is Where Theory Starts Becoming Troubleshooting
This might be one of the most important labs we’ve done so far.
Because we’re connecting everything.
Week 2:
Here are the tools.
Week 4:
Here’s the meter. Here’s a wiring diagram.
Week 5:
Use them.
The students weren’t troubleshooting a customer’s failed air conditioner.
Not yet.
We controlled the environment.
We knew the components.
We knew what the circuit was supposed to do.
But the thinking process is the same one they’ll eventually use in the field.
What should be happening?
What is actually happening?
Where did those two things stop matching?
That’s troubleshooting.
And once that way of thinking starts to click, HVAC gets a whole lot more interesting.
See You in Week 6
We’re documenting the Klein Trade Program week by week inside A/C University.
These weekly articles show what we’re actually doing in class — including the labs, the mistakes, the questions, the stuff that worked, and the lessons that don’t necessarily show up on a certificate.
Eventually, we’ll build a deeper A/C University lesson specifically around electrical troubleshooting.
When we do, we’ll come back and connect it here.
For now?
You’ve got a disconnect.
A transformer.
A thermostat.
A float switch.
A capacitor.
A motor.
A wiring diagram.
And a meter.