Reefer temperature settings, pre-cooling and how long a unit runs on a tank

Shipper instructions come first

Every reefer load comes with two settings: the setpoint (the temperature to hold) and the mode (continuous or cycle). Both come from the shipper. You'll find them on the bill of lading, and they should match the rate confirmation. If they don't, stop and get it fixed before loading; a mismatch is where many temperature claims start.

Under the FDA's sanitary transportation rule (21 CFR 1.908(e)), a carrier that has agreed to be responsible for temperature control has to meet the shipper's specifications and, if asked, show the temperature was held. So the shipper decides, you run it, and the controller's download proves it.

Typical temperatures, as guidance only

These ranges come from handling guides, not rules. The shipper's number on the paperwork always wins.

Notice how many items are hurt by too much cold. Setting a tomato load at 34°F "to be safe" can cause chill damage and a claim. For more commodities, USDA's Agriculture Handbook 66 is the standard reference.

Continuous vs cycle mode

Thermo King calls its cycle mode Cycle-Sentry and Carrier calls it start-stop; drivers often just say "cycle." Running cycle on a load marked continuous to save fuel is a common way to lose a claim.

Pre-cooling steps

Pre-cooling means running the empty trailer down to setpoint before loading. Under 21 CFR 1.908(e)(3), a carrier responsible for temperature control must pre-cool each refrigerated compartment as the shipper specifies. A simple routine:

1. Check the paperwork for setpoint, mode and whether pre-cool is required.
2. Inspect the trailer: clean, dry, no odor, drain holes clear, door seals intact, air chute undamaged.
3. Set the unit to the shipper's setpoint and mode.
4. Close the doors and run it. Leave plenty of time; the walls and floor have to cool, not just the air.
5. Watch the return air reading. When it reaches setpoint, the box is ready.
6. Back in and keep doors closed until the dock is ready. Open doors dump the cold you just paid for.
7. Record it: the time the trailer reached setpoint, on the bill of lading or in your notes.

How long does it take a reefer to cool down?

There's no single answer. A modern unit is strong (Thermo King's S-610DE spec lists 55,000 BTU per hour of cooling at a 35°F box in 100°F ambient conditions, and 30,000 at 0°F), but an empty trailer still holds heat in its walls and floor. A chilled setpoint on a cool morning comes down quickly; a frozen setpoint at a Texas dock in July takes a lot longer. Our desk plans pre-cool well ahead of every appointment, usually an hour or more for chilled and longer for frozen, and has drivers confirm the return air reading before backing in.

Reefer fuel consumption

A trailer unit burns fuel by the hour. EPRI describes diesel transport refrigeration units as typically 8 to 38 horsepower and burning up to about a gallon an hour. Your actual burn depends on:

• Setpoint: frozen burns more than chilled.
• Outside temperature: hot days and direct sun raise it.
• Mode: continuous burns more than cycle.
• Door openings: multi-stop loads burn more.
• Unit age and condition: dirty coils and worn parts cost fuel.

The best number is your own. Note the gallons and the unit's hour meter at each fill-up; gallons divided by hours is your real burn rate. The tax side of reefer fuel (dyed diesel, IFTA and penalties) is in what is reefer fuel?.

Run time on a tank

How long a reefer runs on a tank is simple division: tank size divided by burn rate. Thermo King offers 30 and 50 gallon tanks on the S-610DE.

These are full-tank figures. Plan to fuel well before empty: running the unit dry warms the load, and restarting a unit that ran out of fuel can take time you don't have. Put your own numbers into the reefer fuel burn calculator to get gallons and cost for a specific load.

Reefer fuel is a cost every reefer load carries that a dry van load doesn't, so it belongs in your minimum rate. Our reefer rates guide shows how to fold it in. For how the unit itself works, see what is a reefer truck?, and for how we find loads that pay for all of this, see reefer loads.