It’s 1 a.m., you’re 200 miles from the receiver, and the reefer display is flashing a number you’ve never seen. Half the drivers on the road do one of two things here: ignore it until morning, or panic-call dispatch with no information.
Both are wrong. The right move takes about ten minutes, and it starts with understanding that not all alarms mean the same thing — the unit is already telling you how urgent it is, if you know how to read it.
1. Alarms Come in Tiers, Not One Flavor
Thermo King’s own alarm-code reference sorts every code into three levels, and the logic carries over conceptually to other makes:
| Level | What it means | What the manufacturer tells the operator to do |
|---|---|---|
| Green / Log | No alarm, or informational | No action needed |
| Yellow / Check | Something’s off, unit still running | Monitor temperature manually, report at end of day |
| Red / Immediate | Serious fault, unit may be shut down | If the unit is shut down, repair immediately |
Carrier’s APX controller uses the same idea in words instead of colors: a non-shutdown alarm shows “CHECK AT NEXT SERVICE INTERVAL,” while a shutdown fault says so outright.
So the first question is never “what does code 18 mean?” It’s: is the unit still running, and is the box still holding temperature? Everything else follows from that.
2. The Codes Drivers Actually See (Thermo King examples)
A sample from Thermo King’s published alarm list, with the operator action the manufacturer specifies:
- 00 — No alarms exist. Nothing to do.
- 02 / 03 / 04 — Check evaporator coil, return air, or discharge air sensor. Yellow. Monitor temps manually, report at end of day.
- 08 — Unit running on coil sensor. Yellow. The unit switched to a backup sensor. Monitor manually.
- 09 — High evaporator temperature. If the unit shut down, it’s an immediate repair. Otherwise report at end of day.
- 10 — High discharge pressure or temperature. Red. Often airflow or condenser related.
- 12 — Sensor or digital input shutdown. Red. The unit cannot operate. Repair immediately.
- 17 — Engine failed to crank. Frequently fuel, battery, or cold-start related.
- 18 — High engine coolant temperature.
- 64 — Pre-trip reminder. Not a failure. Run the pre-trip.
- 66 — Low engine oil level.
Note the pattern: sensor codes are usually “keep driving, keep watching.” Pressure, shutdown, and engine codes are “stop guessing, make a call.”
One more worth knowing even though it isn’t an alarm code on every unit: running the reefer fuel tank dry. If it loses prime, restarting can require a service call — an entirely avoidable expense that also puts the load at risk. Some units offer fuel monitoring that warns you first; most of the time, the warning is you looking at the gauge.
3. Your First 10 Minutes, in Order
- Write the code down. Exactly as displayed, plus the time. Manufacturers explicitly ask operators to record every alarm so the technician isn’t diagnosing blind.
- Check whether the unit is running. Fans turning, compressor engaged, set point still correct?
- Check the box temperature — return air and, if you can, supply air. An alarm with temps still in range is a very different conversation than one with a climbing box.
- Check the reefer fuel level. A surprising share of “it just quit” calls are an empty reefer tank.
- Look for the physical cause. Door seal ajar, plugged condenser, ice on the evaporator, airflow blocked by pallets past the load line.
- Photograph the display. Code, box temp, set point, fuel level — one photo covers all four and time-stamps itself.
- Then call dispatch with: code, running or shut down, current box temp, set point, fuel level, commodity, and hours remaining to the receiver.
That last step is why the first six matter. A dispatcher who hears all seven facts can make a decision in one call. A dispatcher who hears “the reefer is beeping” cannot.
4. Decide Early Whether the Load Is Still Deliverable
If the box has drifted out of range, time is the variable you control. Under the FDA’s sanitary transportation rule, once anyone becomes aware of a possible material failure of temperature control, the food can’t simply continue on as if nothing happened — the shipper and receiver need to be in the loop so the product can be evaluated.
Practically, that means:
- Report the excursion while you’re still driving, not at the dock.
- Keep the download intact — do not clear alarms unless a technician tells you to.
- Ask dispatch whether a service stop, a trans-load, or running hard to the receiver protects the load best. Distance, commodity, and remaining thermal mass all change the answer.
- Log everything: when the alarm appeared, what the temperature was, who you called and when.
A temperature event that is reported early and documented well often resolves as a delivered load. The same event discovered at the dock by a receiver’s probe usually resolves as a claim.
5. The Pre-Trip Habits That Prevent Most Alarms
Most codes you’ll ever see trace back to something that was visible before the load:
- Run a full pre-trip on the reefer unit, not just the tractor, and don’t dismiss code 64 when it asks for one.
- Keep the condenser and evaporator coils clean — restricted airflow is behind a lot of high-pressure and high-temperature faults.
- Check reefer fuel every time you fuel the truck. Treat it as part of the same stop.
- Inspect door seals, liner, floor channels, and drains. Air has to move under the load.
- Watch belts and oil level on the unit’s engine, and listen to the pull-down: knocking, surging, or a defrost that never engages is a shop visit you get to schedule instead of one that schedules you.
Reefer Support at MBH Express
At MBH Express Inc, refrigerated freight isn’t a side business — it’s the whole business. Our drivers run modern, well-maintained reefer equipment with ELD and GPS, and they get 24/7 dispatch with backup trucks when something goes wrong at 1 a.m. We’d always rather take the call early than read about it on a rejection notice.
Drivers here are paid for all miles, loaded and empty, run 2,500–3,300 miles per week across the Midwest, South, and East, and get weekly direct deposit.
Want a reefer seat where someone actually answers the phone? Call +1 (219) 343-6004 or apply online.