The Duty-Cycle Questions to Ask Before You Drive Out
Why this matters
A dispatcher books a standard slot, a tech drives out, runs the system for the length of the slot, finds nothing, and the shop eats the trip. The information that would have prevented that was available on the intake call and nobody asked for it. Duty cycle, meaning how much of the time the equipment is actually running and how hard, sets how long your visit has to be, when in the day you should arrive, and what you need on the truck. It is the cheapest scheduling input you have and most intake scripts never touch it.
Duty cycle is a fraction, not a feeling
Duty cycle is run time divided by elapsed time, expressed as a percentage. A unit that runs 20 minutes out of every hour is at about 33 percent. A unit that never shuts off is at 100 percent and is telling you something on its own.
Customers do not think in fractions. They say "it runs all day," which usually means it is energized all day, not running all day. The gap between those two is where the diagnosis lives. Your job on intake is to convert the feeling into a fraction using things the customer genuinely knows: what time it comes on, what time it goes off, how often they hear it start, and roughly how long each run lasts.
Two of those four are usually enough. Starts per hour multiplied by minutes per run gives you minutes of run per hour, and that divided by 60 is your duty cycle.
The six questions, and what each one changes
| Question | What it tells you | What you do differently |
|---|---|---|
| What time does it come on and what time does it stop for the day? | Elapsed window, and whether the complaint window sits inside it | Sets the earliest useful arrival time |
| How often do you hear it start, and how long does a run last? | The actual duty cycle | Sets slot length and whether you must force continuous run |
| How long after it starts does the trouble show up? | Incubation time | Sets test duration at 1.5 times this figure |
| Once it acts up, how long before it works again, and does anyone have to touch anything? | Thermal recovery versus a latched device | Points at mechanism before you arrive |
| Has the schedule, the load, or the occupancy changed in the last few months? | Whether duty cycle moved recently | Reframes a "sudden failure" as a system that was always marginal |
| Is anything else new that makes it work harder? | Added demand you would otherwise never see | Prevents fixing a healthy unit that is simply over-asked |
Ask them in that order. The first two build the fraction, the third sets the clock, and the fourth is the one that pays.
The recovery question is the one that pays
"How long before it works again, and does anyone have to touch anything?" separates two mechanisms that look identical from the customer's side and require completely different visits.
It comes back on its own after a wait. That is thermal. Something heated past a limit, a protector or a control opened, and it has to cool before it will close again. Recovery times measured in tens of minutes are the signature. The longer the recovery, the more mass is involved, which narrows down which component you are hunting.
Someone has to press, flip, or cycle something. That is a latched device or a fault code that needs clearing. It may still be heat-caused, but the mechanism includes a lockout, which means there is often a stored fault history on the equipment worth reading before you touch anything.
It comes back instantly with no wait and no action. That points away from heat entirely and toward something momentary: a supply disturbance, a control glitch, a mechanical event that cleared itself.
Three answers to one question, three different trucks-worth of preparation.
Turning answers into a dispatch decision
| Duty cycle picture | Slot length to book | Arrival timing | What to bring |
|---|---|---|---|
| High duty, near continuous, fault well into the run | 1.5x the reported time to fault | Any time, it will be running | Logging instruments, expect to sit |
| Low duty with a busy block | Long enough to force continuous run, not to wait for it | Just before the busy block starts | Means to load the system, plus loggers |
| Cycling complaint, many short starts | Enough for 4 to 6 full cycles | During the customer's normal operating pattern | Start-side test gear |
| Fault at startup only, never mid-run | Standard slot is fine | First thing, from a cold system | Nothing special |
| Duty cycle changed recently | Standard slot plus time to survey the load | While the new load is present | Capacity and load measurement |
The second row is the one shops get wrong most often, and it is worth its own paragraph. When duty cycle is low but the fault needs accumulated run time, waiting for the fault in real time can take most of a day. Forcing continuous run compresses that into a couple of hours, but only if you arrive with a way to hold the system in demand. Show up without that and you are back to waiting.
The worked example
A small commercial site reports that their water heating appliance goes lukewarm in the afternoon and recovers by the next morning. The office wants to book the standard one hour slot.
The intake conversion, using the customer's own answers. The unit is energized 12 hours, roughly 7 in the morning until 7 in the evening. During the busy block, which they put at about 4 hours over the middle of the day, they hear it start about 5 times an hour and each run lasts about 4 minutes. That is 20 minutes of run per hour, so about 33 percent duty during the block. Outside the block they hear it once an hour for the same 4 minutes, so about 7 percent.
Total run time for the day: 4 hours at 33 percent is about 80 minutes, and the remaining 8 hours at 7 percent is about 32 minutes. Roughly 112 minutes of actual run inside a 12 hour energized window, which is under 16 percent overall duty. The customer's "it runs all day" was off by a factor of six.
Now the third question. The trouble shows up near the end of the busy block, not at a fixed clock time, and on a slow day it does not show up at all. That tracks accumulated run time, not the hour of the day.
And the fourth. It comes back on its own by the next morning and nobody touches anything, but a shorter break in the middle of the day, half an hour or so, does not fix it. Long recovery with no manual reset. Thermal, with meaningful mass involved.
Now do the dispatch arithmetic. The fault needs something close to the 80 minutes of run the busy block delivers. At 33 percent duty, accumulating 80 minutes of run takes about 4 hours of elapsed time, which is why the customer only sees it in the afternoon. A standard one hour slot at that duty would deliver about 20 minutes of run, a quarter of what the fault needs, and would pass clean every single time.
So the booking becomes: arrive 30 minutes before the busy block, book a three hour slot, and plan to force continuous run rather than wait. Target run duration is 1.5 times 80 minutes, so about 2 hours of continuous operation, which fits inside three hours with setup and teardown. Bring the means to hold the system in demand and something that logs temperature over time.
Compare the two paths in hours. The wrong booking is a one hour visit that finds nothing, plus drive time, plus a second visit that has to be the three hour one anyway. The right booking is one visit at three hours. Even before the customer's opinion of you enters the picture, asking four questions on the phone saved more than an hour of shop time and one round trip.
The questions that sound useful and are not
"How old is it?" Age correlates with nothing you can act on before arrival. A five year old unit at 80 percent duty in a hard environment is older, functionally, than a fifteen year old unit that runs an hour a day. Ask about duty first and let age inform the repair-versus-replace conversation later.
"When was it last serviced?" Useful for the file, useless for the visit plan. It changes what you suspect, not how long you need to stay or when to arrive.
"What brand is it?" Only matters for parts availability. It does not size the visit.
"Is it under warranty?" A billing question, not a diagnostic one. Ask it, just do not let it displace the four that set the visit.
None of these are bad questions. They are bad first questions, and intake calls run out of the customer's patience long before they run out of your list.
What doing this wrong looks like
The signature is a run of tickets on the same site, all short, all clean, and a complaint that never resolves. The tech's notes are correct and the visits were the wrong shape. Each one tested a system that had barely run.
The second signature is the opposite error: a shop that overcorrects and books every intermittent call as a half-day. That burns capacity on faults that genuinely appear in the first five minutes, and it teaches the office to stop asking, because the answer never changes the booking anyway. The point of the questions is that they discriminate. If your dispatch never changes based on the answers, you are collecting data for nothing.
Catch both by auditing your no-fault-found tickets once a quarter. Pull them, and for each one write the duty cycle and the reported time to fault next to the slot length that was booked. Any ticket where the slot could not physically have delivered enough run time is a dispatch failure, not a diagnostic one, and it is fixable on the phone.
How to verify the intake was good enough
Three checks before the job leaves the office.
You can state the duty cycle as a number, even a rough one, in the ticket notes. Not "runs a lot." A percentage or a minutes-per-hour figure.
You can state the incubation time and show that the booked slot is at least 1.5 times that figure of actual run, not of elapsed time. Those are different numbers whenever duty is under 100 percent, and confusing them is the most common way a well-intentioned longer booking still fails.
You can name which recovery pattern the customer described, and therefore what the tech should read or measure first on arrival. If the notes cannot answer that, call back before you dispatch. One more minute on the phone is cheaper than any windshield time.
References
- Manufacturer documentation on rated duty cycle, continuous-duty ratings, and thermal protection reset behavior
- Trade-standard practice for service-call intake and dispatch triage
- See related: Why a Short Test Cycle Passes a Failing System
- See related: How to Separate Runtime-Driven Faults From Ambient-Driven Ones
- See related: How to Question a Customer to Pin Down When a Fault Happens