Reefer unit diagnostic checklist
By Vimal Bhaya, Founder and Lead Systems Architect · Last reviewed 18 October 2026
Pick what you see, answer a few yes or no checks, and this checklist names the most likely reason your reefer is acting up, how urgent it is, and the exact spot in the troubleshooting guide that explains it.
It covers a load that will not hold, defrost alarms, a box that warms at each stop, a unit that will not restart and a parked trailer warming on shore power. Nothing you tap is stored or sent anywhere.
The checklist starts with what you see
Pick the one closest to what is in front of you. The checklist then asks one yes or no question at a time, in the order the troubleshooting guide lists the reasons.
- The load will not hold temperatureToday. On the road, now
- A defrost alarm, ice at the drains, or defrosts too oftenWithin the trip. Red alarms now
- The box warms at each stop, or one end of the load is warmThis trip
- The unit shuts down, or will not restartNow. A stopped unit is not cooling
- A parked trailer on shore power stops coolingNow
The questions come from the troubleshooting guide, in its order
Every question comes from the checks on Reefer troubleshooting, and the checklist is built from the same file, so the two always match. It covers the five symptoms and 19 reasons on that page.
The first yes is the most likely reason, and the result links straight to it. You can keep going to check the rest. If nothing fits, the checklist names the reasons only a technician can check, and the short list to run through before you call.
Every question can be answered from outside the trailer or at the controller. Switch the unit off at the controller before clearing anything, keep someone outside the doors, and never shut yourself in a trailer.
For a health check when nothing is wrong yet, the guide also has a short list of checks for a healthy reefer.