The Human Diagnostic
Looking for honest stories about people, not product reviews? You're in the right place.
The Human Diagnostic isn't a how-to HVAC podcast. It's what a 45-year Master Technician notices about people after 90,000 service calls across gas plants, oil rigs, hospital preservation systems, high-rises, feedlots, walk-in freezers, and residential homes all over Central Oklahoma.
Hosted by Dave Hartzell, each episode tells a real story from a real service call. Sometimes he's driving to the job and predicting what he's about to walk into. Sometimes he just left and he's still working through what he saw. Either way, the story turns out to be about more than HVAC.
Topics you'll hear across the season:
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The customer nobody wanted to take, and what changed when someone finally did
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Why the person researching their broken AC at midnight isn't being difficult, they're scared
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What 45 years of walk-ins, weddings, funerals, and broken water heaters teaches you about anxiety
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The tech who can fix anything but can't explain it, and why the customer doesn't trust him
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The review you can't place, the moment you never forget, the call that changed how you work
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What gets lost when we treat people like tickets, and what gets found when we don't
Whether you fix things for a living, manage people who do, or just like good stories from someone who has been everywhere and met everybody, The Human Diagnostic gives you the part of the job that never shows up in an invoice.
π Proudly based in Kingfisher and serving Edmond, Guthrie, Yukon, Mustang, Piedmont, Logan County, Canadian County, Blaine County, Major County, Garfield County, and the greater Oklahoma City metro area. Hartzell's Heat & Air blends old-school integrity with cutting-edge technology, from digital diagnostics to smart-home HVAC integrations.
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Every call is a story. Every story is a person.
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The Human Diagnostic
Why a Fixed Furnace Still Sounds Broken to You
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She called me back four times in one evening, and the system was already working when she made the second call.
It was a furnace that wouldn't cycle right. October, the first real cold snap, the kind that comes in overnight and makes everybody remember they have a furnace at all. She lived alone in a brick ranch out past the school, and the unit was throwing a fault every few hours. Heat, then nothing, then heat again. I got there in the afternoon.
The blower wheel was packed with dust and a limit switch was nuisance-tripping on the high side. I cleaned the wheel, swapped the switch, watched it run through three full cycles standing in her hallway with my hand on the supply register feeling the air come warm and steady. The flame was clean. The amp draw was where it belonged. I told her it was fixed, and it was fixed.
She thanked me. She walked me to the door.
And then, as I was pulling the latch shut behind me, she said: but it'll keep doing that thing, right, that clicking.
There was a click. Old furnaces click. The gas valve seats, the relay drops out, the metal in the heat exchanger ticks as it cools. I'd heard it the whole time I was standing there. To me it was the sound of a furnace working. To her it was the sound of the thing that had broken.
I told her the click was normal. I stood in the doorway and explained it, the metal expanding and contracting, the relay, all of it. She nodded. She said okay.
She called the shop at six. The furnace clicked. Was that the problem coming back.
I called her, walked her through it again, told her to listen for heat, not for the click. She said okay.
She called at seven-thirty. Then at nine. By the fourth call she wasn't even asking a question anymore. She just wanted to describe the sound to me, the exact texture of it, so I could tell her one more time that it was nothing.
Core line: "I could have been right forty times over the phone and it wouldn't have closed anything, because being right from a distance doesn't shut the loop."
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Have you ever like proved a problem is 100% solved? I mean, checking all the boxes, showing the absolute undeniable data.
SPEAKER_01Aaron Powell Oh, yeah. Like you show them the actual map.
SPEAKER_00Right. You walk them through the logic, you prove everything is fine, and yet they just stare blankly at you in total panic.
SPEAKER_01Yeah, their brain just um completely refuses to let go of some tiny unexplained detail.
SPEAKER_00Aaron Ross Powell Exactly. Why do our brains do that? Today we're going on a deep dive into this super frustrating gap between, you know, a mechanically perfect repair and a psychologically broken human.
SPEAKER_01Aaron Powell It's such a fascinating intersection, really. Trevor Burrus, Jr.
SPEAKER_00It is. And our source material today is this incredible account from Dave Hartzell. He's a master HVAC technician out in Kingfisher, Oklahoma, with uh 45 years of experience.
SPEAKER_01Aaron Powell 45 years. I mean, you don't just learn about broken machines in that time. Yeah. You learn about the people who own them.
SPEAKER_00Aaron Powell Yeah, exactly. And our mission today is to really figure out the difference between a problem that is technically solved and a problem that actually feels close to the person dealing with it. So okay, let's unpack this by starting with Dave. A sudden drop in the Oklahoma temperature and a very, very persistent customer.
SPEAKER_01Aaron Powell Right. So we have to set the stakes here. It's October.
SPEAKER_00The first cold snap, right.
SPEAKER_01Exactly. It's that first real biting overnight freeze where everybody suddenly remembers, oh wow, winter's here and I absolutely need a working furnace.
SPEAKER_00Yeah, there's that like visceral vulnerability of being cold in your own house. It just changes your whole mental baseline.
SPEAKER_01It really does. You're physically uncomfortable and you feel unprotected. So Dave gets called out to this brick ranch house during this exact cold snap, and there's a woman living there all by herself.
SPEAKER_00Aaron Powell And her furnace is doing this thing. I think the trade term in the source is nuisance tripping.
SPEAKER_01Yeah, nuisance tripping.
SPEAKER_00Yeah. Right. Which basically means for anyone not, you know, deeply versed in HVAC stuff, the furnace turns on, gives a little burst of heat, but then it detects that it's getting too hot inside its own casing. So it does an emergency shutoff just to prevent a fire.
SPEAKER_01Aaron Ross Powell So you get this brief moment of hope with the warm air and then just dead silence over and over.
SPEAKER_00Just sitting alone in a freezing house listening to your machine fail sounds awful.
SPEAKER_01It is. But Dave arrives that afternoon, and I mean he's a master tech. He diagnoses it perfectly in minutes.
SPEAKER_00Because it's a physical mechanical issue.
SPEAKER_01Exactly. He finds the blower wheel is just totally packed with years of dust. Yeah. And the limit switch, which is the sensor that triggers the shutoff, is just bad. It's reading the temperature wrong.
SPEAKER_00So he just strips it down and fixes it. He cleans the wheel, swaps the switch for a brand new one, and then he literally stands there holding his hand over the floor register, feeling this perfect, steady heat pouring into the room.
SPEAKER_01The machine is fixed. I mean unequivocally fixed.
SPEAKER_00Yeah. He watches it run through three totally flawless cycles. He even puts his multimeter on it to check the amp draw, checking the electrical current. It's exactly what the manufacturer specs say it should be. The flame is bright blue. It's a mechanically perfect furnace.
SPEAKER_01He solved it. He tells her the good news, she thanks him, and they walk to the front door.
SPEAKER_00But this is where the whole vibe of the afternoon just shifts.
SPEAKER_01Right at the door.
SPEAKER_00Right at the door. He's about to pull the latch, head to his truck, and she stops him. She completely fixates on a sound.
SPEAKER_01This tiny little sound.
SPEAKER_00She says, but it'll keep doing that thing, right? That clicking.
SPEAKER_01And for Dave, with almost half a century of experience, he knows exactly what that microscopic click is.
SPEAKER_00It's just what old furnaces do, right?
SPEAKER_01Exactly. When the heating cycle finishes and it starts to cool, the metal heat exchanger physically expands and contracts. Plus, there's an electrical relay that drops out to cut power, and a heavy gas valve that drops back into its seat.
SPEAKER_00Right, to stop the fuel. So to Dave, that click is literally the sound of safety. It's the audible signature of the machine working flawlessly.
SPEAKER_01But to her, it's the sound of the furnace breaking all over again.
SPEAKER_00Because she doesn't have the mechanical vocabulary for it. She doesn't hear metal contracting, she just hears an anomaly.
SPEAKER_01And Dave does what any logical expert would do. He stops, turns around, and explains the physics to her.
SPEAKER_00He gives her the facts.
SPEAKER_01Yes. He explains the heat expansion, the relay, the valve. She nods, says she understands, and Dave finally goes home.
SPEAKER_00But uh she definitely didn't let it go. The source material outlines this wild behavior after he leaves. She calls his shop at six o'clock that evening.
SPEAKER_01Oh wow.
SPEAKER_00Yeah, asking if the problem is coming back because it clicked again. Dave patiently walks her through the physics a second time.
SPEAKER_01Trying to logic her out of it again.
SPEAKER_00Right. He tells her, you know, focus on the warm air, not the click. She says, okay. But then her name pops up on the caller ID again at 7 30.
SPEAKER_01Oh no.
SPEAKER_00And then again at nine.
SPEAKER_01Four separate phone calls in one evening about a perfectly functioning machine.
SPEAKER_00And by that fourth call, the source note, she isn't even asking questions anymore. She just wants to describe the quote exact texture of the sound to him. Meanwhile, her house is totally warm. The filmostat is holding steady.
SPEAKER_01Everything measurable is perfectly fine.
SPEAKER_00Right, but she's completely anchored to this noise. And um, I have to push back a little here because reading this, my first instinct is like, isn't she just being unnecessarily difficult? Or maybe she just has extreme anxiety.
SPEAKER_01It's easy to jump to that conclusion for sure.
SPEAKER_00It just sounds exactly like WebMD paranoia. You know, when a doctor looks at your chart, runs your blood work, and says, hey, this cough is just a normal seasonal cough, but you go home and you just keep clearing your throat every five minutes to check if it's getting worse because you read some terrifying article.
SPEAKER_01Oh, totally. WebMD paranoia is a great analogy.
SPEAKER_00Yeah.
SPEAKER_01It captures that exact hypervigilance, that impulse to check for disaster, even when you have a clean bill of health. But we really have to reframe her behavior here. She isn't just acting out of pure irrational anxiety. She isn't No, and she certainly isn't trying to harass Dave. We have to separate the machine from the mind. Mechanically, yes, the repair is closed. But psychologically, for her, this event is wide open.
SPEAKER_00Oh, I see. So she's not actively rejecting his expertise. She just literally lacks the cognitive ability to put the experience down.
SPEAKER_01Exactly. She is trapped in a cognitive loop. And this inability to let go of an unexplained detail isn't just a quirk of this one homeowner. It's a deeply embedded feature of the human brain. To understand why she thinks a harmless click is an emergency, we have to look at how memory processes unfinished tasks.
SPEAKER_00Which takes us far away from Oklahoma.
SPEAKER_01Yes, thousands of miles away and a century back in time.
SPEAKER_00Right, to the 1920s. Imagine this bustling, noisy, smoke-filled coffee shop in Vienna or Berlin. The historical accounts debate that detail.
SPEAKER_01The setting doesn't matter as much as the chaos. It's a busy European cafe.
SPEAKER_00Yeah, and sitting at a table is a young psychologist named Bluma Zygarnik, along with her university professor. They are just watching the waiters navigate this chaotic floor.
SPEAKER_01And these waiters are taking incredibly complex orders from large tables. Multiple drinks, specific side dishes, modifications.
SPEAKER_00And they are holding all this dense information perfectly in their heads without writing a single thing down.
SPEAKER_01Which is impressive on its own.
SPEAKER_00But here is the catch they noticed. The waiters have this flawless memory right up until the exact moment the bill was paid. And then the second the table settled up, the memory just vanished. It evaporated. If Zygarnik asked a waiter five minutes later what table four had ordered, they couldn't name a single item.
SPEAKER_01The data was just wiped.
SPEAKER_00Wiped clean, paid was gone, open was remembered.
SPEAKER_01And Zygarnik was captivated by this. Why does the brain hold on to so much data and then just violently dump it? So she took this to her lab in 1927 and published a really foundational study.
SPEAKER_00What did she do in the lab?
SPEAKER_01She gave subjects simple tasks, you know, basic math, stringing beads, simple puzzles, but she introduced a catch. She deliberately interrupted them partway through some tasks, physically preventing them from finishing.
SPEAKER_00Oh, that sounds frustrating. And then she tested their memory afterward.
SPEAKER_01Right. And the results were staggering. People remembered the interrupted, unfinished tasks about twice as well as the ones they actually completed. What's fascinating here is the core mechanism of what psychology now calls the zygarnic effect.
SPEAKER_00Zygarnic effect.
SPEAKER_01Yes. When a task is unfinished, it stays lit up in the mind. And evolutionarily, this makes total sense.
SPEAKER_00How so?
SPEAKER_01Well, forgetting an unfinished task like failing to secure your shelter before nightfall or losing track of a predator was biologically dangerous. Our brains evolved to burn precious calories, keeping unresolved threats active. It keeps a little mental current running in the background, nagging us because it needs action. We naturally hold onto the open loop and drop the closed one.
SPEAKER_00Wow, that evolutionary perspective completely changes how you look at the woman with the furnace. That clicking sound is her unpaid bill.
SPEAKER_01Exactly. It's the uncompleted puzzle.
SPEAKER_00Dave gave her the heat, he swapped the switch, but because she didn't have a personal answer for that specific click, it acted as a psychological thumbtack. It just pinned the entire heating task open in her mind. Her brain is treating the furnace like an interrupted survival task.
SPEAKER_01Yes, keeping the threat lit up to protect her. The cognitive tension just couldn't release. As long as there's a physical sound she couldn't account for, that file stayed open on her mental desktop, drawing power, drawing attention, and generating those four frantic phone calls.
SPEAKER_00So now that we understand the deep brain mechanics here, how does a technician actually deal with it? Dave's job is fixing metal, not being a cognitive behavioral therapist. True. But interestingly, Dave had to look in the mirror and examine his own brain first to figure this out.
SPEAKER_01Yeah, Dave had this profound revelation about his own career. He realized he isn't immune to this garnik effect either.
SPEAKER_00Not at all.
SPEAKER_01When he thinks about the service calls that, you know, ride home in the truck with him at the end of the day, it's never the incredibly hard, exhausting jobs that took him six hours to fix.
SPEAKER_00Right, because those grueling jobs that he fixed, those are closed loops. They're paid bills. He doesn't think about them over dinner.
SPEAKER_01Exactly. The calls that actually haunt him, the ones he ruminates on in bed, are the open ones. The unpaid bills. Yes. The intermittent electrical fault that just refused to show up while he was standing there with his tools, or the tiny refrigerant leak he couldn't find before dark, so he has to come back on Tuesday. He feels that exact same cognitive pull, that mental current that the woman feels about her click.
SPEAKER_00He feels the weight of the unfinished task. But wait, I have to challenge this sequence of events a bit. If Dave understands exactly what an open loop feels like, and he absolutely knows for a fact that the click is harmless, why didn't his expert reassurance over the phone work? He walked her through the physics of the metal expanding like three or four separate times.
SPEAKER_01Yeah, he tried his hardest.
SPEAKER_00Why isn't a master technician's word enough to pay the mental bill and shut down the zygarnik effect?
SPEAKER_01Ah, this brings us to a really crucial distinction. It's what we can call the failure of remote correctness.
SPEAKER_00Remote correctness.
SPEAKER_01Right. Being right from a distance doesn't shut a psychological loop for someone else. When Dave is on the phone saying, I promise you it's fine, it's just the heat exchanger, he is throwing logical facts at an emotional open loop.
SPEAKER_00And facts don't equal closure.
SPEAKER_01Exactly. Think about our own lives. A partner texts you, incredibly stressed, about a work conflict, and you text back a bulleted list of logical solutions. You're technically correct, but your response usually just infuriates them.
SPEAKER_00Oh, I've definitely done that. It's like throwing water at a grease fire. You're trying to help, but you're using the totally wrong material for the specific type of fire in front of you.
SPEAKER_01Because ironically, telling someone a thing is fine over the phone actually keeps the loop warm.
SPEAKER_00Wait, it keeps it warm?
SPEAKER_01Yeah, it keeps the clicking sound as the active topic of conversation. It engages the worry without resolving who actually gets to declare the event over. When Dave says it's fixed over the phone, he's trying to use his authority to close it for her. But just like the waiters in Vienna, the current is running in her brain, not his.
SPEAKER_00You can't force someone else's cognitive cash register to open from across town.
SPEAKER_01Beautifully put.
SPEAKER_00So if both the tech and the customer suffer from these open loops and just chucking facts at them over a phone line actively makes it worse. What is the actual mechanism for closure? How do you turn off a current in someone else's brain?
SPEAKER_01Aaron Powell You have to fundamentally change the physics of the interaction. You have to abandon remote correctness entirely and move the person from observation to physical participation.
SPEAKER_00Which requires Dave to stage an intervention with himself, basically. He realizes you cannot close a loop in another person by simply, quote, being correct at them.
SPEAKER_01Being correct at them. Such a perfect phrasing.
SPEAKER_00Right. So he stops trying to talk it closed over the phone. But wait, so he gets back in his truck in the dark, drives all the way back out to her house, and he doesn't explain the metal expanding again. What does he actually do?
SPEAKER_01The intervention he designs is entirely tactile. It's no longer a conversation about physics, it's a physical demonstration of closure. When he arrives, no lecture on thermodynamics. He walks over to the furnace and has the woman stand right next to him. He takes her hand and physically places it on the exterior metal cabinet.
SPEAKER_00He wants her to feel the vibration of the exact moment the click happens.
SPEAKER_01Yes. And more importantly, he wants her to feel that the click happens while the hot air is still actively pouring into the house. He is proving, through her own physical senses, that the click happens alongside the heat, not instead of it. Wow. He makes her run the entire system up and down twice. She walks over to the thermostat, turns the temperature up, walks back, feels the heat, feels the click, then she walks back, turns it down, and feels the click again. And through this entire process, Dave uses the most counterintuitive, powerful tool he has.
SPEAKER_00He stands there and says absolutely nothing.
SPEAKER_01Nothing at all.
SPEAKER_00He doesn't reassure her. He doesn't cross his arms and go, see, I told you it was fine. He removes his own authority completely and makes her the one who confirms the environment is safe. Here's where it gets really interesting. The source material gives us this incredible quote from Dave about this exact moment. He says, The loop shuts when the person holding it gets to set it down themselves.
SPEAKER_01That is just a masterclass in behavioral psychology.
SPEAKER_00It really is.
SPEAKER_01By making her touch the machine, operate the thermostat, and by staying totally silent, Dave transferred the power of closure back to her.
SPEAKER_00She wasn't just taking his word for it anymore.
SPEAKER_01Exactly. She physically experienced the truth. She became the author of the ending.
SPEAKER_00And the result is instantaneous. She never calls again. For the rest of the week, for the rest of that long Oklahoma winter, absolute silence. And it's so critical to point out the furnace had not changed.
SPEAKER_01Not one bit.
SPEAKER_00It was making the exact same metallic click as it was during call one, two, three, and four. The change was entirely within her. The not calling was the physical receipt that the bill had finally been paid in her mind.
SPEAKER_01The cognitive current was turned off.
SPEAKER_00Yeah.
SPEAKER_01The zygarnik effect neutralized because her own nervous system registered the survival task as complete.
SPEAKER_00That's amazing. Dave learned this highly specific, highly tactile technique for dealing with anxious homeowners, but obviously the burden of the unpaid bill goes so far beyond HVAC repair. So what does this all mean for the rest of us? How does this shift the way we help others in our daily lives?
SPEAKER_01Well, it forces us to look around and identify the unpaid bills lingering in our own environments. Dave mentions these everyday domestic things in the source. The strange hollow noise in the hallway at night, the come and go smell near the laundry room, the kitchen breaker that tripped that one time six months ago.
SPEAKER_00And never did it again.
SPEAKER_01Right. These things draw massive amounts of our attention. Attention they frankly don't deserve just because they lack a psychological period at the end of the sentence.
SPEAKER_00They're unpaid bills sitting on the table.
SPEAKER_01Exactly. And connecting this to the bigger picture, think about corporate management or parenting a terrified toddler, or just being a good friend to someone in a crisis. When someone you care about is fixated on a problem, and you know for an absolute fact the problem is solved, you cannot just send them an email of facts.
SPEAKER_00Right. You can't just text them a bulleted list of reasons why they should calm down.
SPEAKER_01Because remote correctness always fails. You must guide them toward physical or psychological participation. You have to create a safe environment where they can examine the evidence, feel the reality, and set that heavy loop down themselves.
SPEAKER_00Sometimes you just have to stand there in total silence.
SPEAKER_01Yes. Let them be the one to declare the task finished.
SPEAKER_00It's like uh trying to teach someone that a bicycle won't tip over by reading them a physics textbook.
SPEAKER_01Oh, that's good.
SPEAKER_00You can show them all the gyroscopic equations in the world. You can read to them over the phone about forward momentum, but you cannot argue them out of their fear of falling.
SPEAKER_01It's biologically impossible.
SPEAKER_00Yeah. They have to sit on the seat, they have to feel the pedals moving under their own feet, feel the momentum pushing back against gravity, and they have to be the one to realize, oh, I am balancing. They have to close the loop.
SPEAKER_01You can provide the bicycle, just like Dave provided the functioning furnace, but the user has to ride it to close the loop.
SPEAKER_00Exactly. To wrap up the narrative of Dave and the customer, the furnace ran beautifully all winter long. And Dave knew it ran fine because she absolutely would have called if it didn't. His job, as he was trained for 45 years, was always fixing the metal. But what he learned that night in October was that the metal is only ever half the job.
SPEAKER_01And the other half is recognizing the open loops in the humans who operate that metal. It's a really profound realization about the nature of our work, whatever that work might be. We're constantly navigating between the mechanical reality of a situation and the psychological reality of the people involved.
SPEAKER_00Which leaves us with a pretty intense final thought for you to mull over today. If the Zygarnik effect dictates that our brains obsessively highlight what is unfinished, and that these open loops drain our mental current, burning calories until they are finally paid, how much of our modern daily exhaustion isn't actually from doing too much physical work?
SPEAKER_01That's a scary thought.
SPEAKER_00Right. How much of our deep modern burnout is actually from carrying around hundreds of microscopic, artificially open loops? I mean, think about the sheer volume of unread email sitting in your inbox right now.
SPEAKER_01Or dangling text conversations you haven't replied to.
SPEAKER_00Yeah, the endless, unceasing stream of app notifications buzzing in your pocket. We are surrounded by thousands of tasks. We've never been given the physical space to mark as paid. Could the entire modern digital world just be one giant, unending furnace click?
SPEAKER_01Just a constant low-level sound that we don't have an answer for, keeping the cognitive loop open forever.
SPEAKER_00It's definitely something to think about the next time your phone buzzes and you feel that little unexplained spike of tension in your chest. Well, thanks for joining us as we unpacked this incredible intersection of machines and minds on this deep dive. Until next time, try to find a few of those open loops today and you know finally mark them paid.