A practical, 2025-ready checklist for setting reefer fresh‑air vents on cabbage, carrots, chilies, and shallots. Includes percent-to-CMH guidance, mixed‑load rules, dehydration vs CO2 balance, and step-by-step adjustments on Carrier PrimeLINE and Thermo King MAGNUM units.
If you’ve ever debated at the dock about opening the vent “a bit more” or “keeping it tight” for vegetables, you’re not alone. We’ve prevented more claims with good vent decisions than with any other single tweak. In our experience, the right fresh air exchange is the difference between crisp, market-ready vegetables and dehydrated, CO2-stressed cargo.
Below is the 2025, hands-on checklist we actually use for Indonesian vegetables. We focus strictly on venting. Not temperature setpoints, not packaging counts.
The 3 pillars of smart vent settings
-
Control CO2 without over-venting. Vegetables respire. CO2 and heat rise in a sealed box. CO2 injury shows up as off-flavors, softening, seed darkening in peppers, and sometimes yellowing. But swinging the vent wide open invites dry outside air that strips moisture. Balance is the game.
-
Vent setting is independent of setpoint. The reefer’s temperature setpoint manages heat removal. The fresh-air vent manages gas exchange. Conflating them ruins loads. We’ve seen setpoints spot-on with cargo still dehydrated because the vent was too open.
-
Verify in CMH (m³/h) when possible. “25% open” means different things on different units. If your controller shows airflow in m³/h, use it. If it only shows percent, convert using the unit’s max fresh-air capacity.
Rule-of-thumb conversions (always check your unit label):
- Carrier PrimeLINE typical max: ≈ 180 m³/h at 100% open. So 25% ≈ 45 m³/h.
- Thermo King MAGNUM Plus typical max: ≈ 200 m³/h at 100% open. So 25% ≈ 50 m³/h.
We always read the door spec plate or controller info for “Max Fresh Air Exchange” to confirm the actual number.
The 2025 vent ranges that work (cabbage, carrot, chili, shallot)
These are pragmatic ranges for full loads in 20ft/40ft containers on typical Indonesia–Middle East or ASEAN routes. If you have controlled atmosphere (CFA/CA) or scrubbers, your numbers may differ.
-
Cabbage (green/round): 15–30 m³/h. Moderate respiration. Needs some exchange to keep CO2 in check on voyages over 7 days, but excessive venting dries wrapper leaves. On dry seasonal routes or strong trade winds, hold to the low end.
-
Carrots: 0–10 m³/h. Low respiration. Very sensitive to dehydration. We often ship closed for long transit when carrots are solo. If mixed with ethylene producers or diesel exposure risk, allow 5–10 m³/h.
-
Chilies (red cayenne): 25–50 m³/h. Moderate-to-high respiration and CO2 sensitivity. Too little exchange can darken seeds and mute flavor. For our Red Cayenne Pepper (Fresh Red Cayenne Chili), we favor 35–45 m³/h on 10–14 day voyages.
-
Shallots (dry bulbs): 0–5 m³/h. Physiology is similar to onions. They prefer drier conditions and minimal exchange. CO2 tolerance is relatively high compared to leafy crops, and dehydration is the bigger enemy. If you also ship onions, you’ll recognize the logic. See our Onion specs for context.
For carrots and chilies, these settings align with what our buyers expect: carrots need water retention; chilies need respiratory gas removal. For carrots and cabbage, you’ll find a similar window if you work with our Carrots (Fresh Export Grade) and standard Indonesian green cabbage.
A simple mixed-load decision rule that actually works
- Start with the most CO2-sensitive or highest-respiring commodity in the mix. That sets your minimum vent rate. In mixed chili + cabbage, chili drives the minimum.
- Cap the vent at what the most dehydration-sensitive commodity can tolerate. In chili + carrots, carrots cap the maximum.
Example: Mixed chili and cabbage. Chili wants 25–50 m³/h. Cabbage tolerates 15–30 m³/h. Set 30 m³/h as a practical compromise. If you see high CO2 in-transit (data logger), bump 5 m³/h up to 35. If you see RH dropping too fast, pull back by 5.
If you’re mixing leafy items with anything else, remember leafy veg are extremely dehydration-prone. Even something as hardy as baby romaine can suffer at high vent. We’ve seen good outcomes by using 15–20 m³/h and compensating with higher carton humidity liners. For reference on leafy handling, see our export-packed Baby Romaine (Baby Romaine Lettuce).
How to change vent opening on your reefer
We’ll keep this focused on the two controllers we see most.
Carrier PrimeLINE (MicroLink):
- Power on. From the main screen, press Menu.
- Navigate to Fresh Air or Vent Setting. Some menus say CFA, FRESH AIR, or VENT POS.
- Select Manual if “Auto/CFA” is enabled. Then adjust the value. Use arrows to set either percent or m³/h depending on your firmware.
- Confirm with Enter. The home screen should briefly show the new vent status.
- Physically verify if your vent has an external indicator. On older units with manual slides, adjust the louver to the tick mark and lock it.
Thermo King MAGNUM Plus:
- Press Menu. Go to Setpoints or Fresh Air/Vent.
- Choose Fresh Air Exchange. Use arrows to set m³/h or percent.
- Confirm and return to the home screen. Look for “FRESH AIR XX m³/h” or “VENT XX%”.
- If your box has a manual-louver assembly, set and reseal after verification.
Tip: Log the setting on the loading photo sheet. We add a tamper seal photo over the vent for claim prevention.
Need help with your commodity, route, and unit model? It’s faster to get it right upstream. If you’d like us to sense-check your plan, just Contact us on whatsapp.
Straight answers to the questions we get most
What vent setting should I use for cabbage in a 40ft reefer?
15–30 m³/h. Go toward 20–30 m³/h for voyages over 7–10 days. If RH trends low or wrapper leaves look papery on arrival, try 15–20 m³/h next time and tighten packaging humidity.
Should I keep reefer vents closed for chilies on long voyages?
No. Chilies need 25–50 m³/h. Closed vents risk CO2 injury, seed browning, and flavor loss. We rarely go below 25 m³/h for full-load chilies.
How do I change the vent opening on a Carrier PrimeLINE?
Use Menu → Fresh Air/Vent → Manual, then set percent or m³/h and confirm. Older units need manual louver adjustment on the exterior vent plate. Always record and photograph.
What happens if CO2 builds up when shipping shallots?
Shallots are tolerant, but high CO2 plus moisture can push condensation, sour odors, and fungal pressure. The larger risk is dehydration from over-venting. We keep 0–5 m³/h and manage moisture with proper pre-cooling and dry airflow, not extra vent.
Can I use one vent setting for mixed chili and cabbage loads?
Yes. Use 30 m³/h as a clean starting point for most routes. Adjust by ±5 m³/h based on CO2 data and RH trends.
Does a higher vent opening increase dehydration risk for vegetables?
Yes. Fresh air is usually drier than the air inside the box. The more you exchange, the faster you pull out moisture. Leafy and cut-surface vegetables suffer fastest. We treat vent opening like a throttle: only as much as the cargo needs to keep CO2 in range.
What’s the difference between reefer setpoint and vent setting?
Setpoint controls temperature. Vent setting controls fresh-air exchange. You can have a perfect setpoint and still get dehydrated cargo or CO2 damage if the vent is wrong. They’re separate tools for separate jobs.
Non-obvious tips that save loads
- Use CMH, not percent, when you can. The same 25% on two units may differ by 10–20 m³/h. That’s the difference between safe and risky on chilies.
- Watch respiration heat as a proxy. If your return air is trending up despite stable ambient, you’re likely under-vented on a high-respiring load. Increase fresh air in 5 m³/h steps and watch CO2 and RH.
- Seal your decision. We put a cable seal or tamper tape on the vent handle after setting. It deters “well-meaning” adjustments at transshipment ports and helps in claims.
Common mistakes we still see (and how to avoid them)
- Using “one-size-fits-all” 25% open. That might be 45–50 m³/h. Great for chilies. Too aggressive for carrots and shallots.
- Chasing ethylene with vent. For carrots, venting to remove ethylene is less effective than not mixing with ethylene producers in the first place. If mixed is unavoidable, use minimal vent plus ethylene-absorbing sachets rather than opening wide.
- Setting for 20ft and assuming it fits 40ft. Gas dynamics differ with volume and load mass. Use CO2 logging on your route and build your own route-specific playbook.
Quick reference: percent-to-CMH estimate
- Carrier PrimeLINE: 100% ≈ 180 m³/h. 10% ≈ 18, 25% ≈ 45, 30% ≈ 54, 40% ≈ 72.
- Thermo King MAGNUM Plus: 100% ≈ 200 m³/h. 10% ≈ 20, 25% ≈ 50, 30% ≈ 60, 40% ≈ 80.
Always validate from your unit’s plate. Some fleets limit max to 160 m³/h for fuel and humidity reasons.
Where this advice applies (and where it doesn’t)
- Applies to: conventional reefers with standard fresh-air vents, non-CA voyages, Indonesian vegetables to ASEAN, East Asia, South Asia, and Middle East lanes of 5–21 days.
- Doesn’t apply if: you’re using Controlled Atmosphere (CFA/CA) profiles, specialized liners, or have unusual packaging perforation rates. In those cases, target CA gas specs first, then treat fresh-air as a secondary lever.
If you want help turning these ranges into a lane- and product-specific SOP for your buying program, we’re happy to review your plan and data logs. Questions about your next shipment? Call us.
And if you’re building mixed programs around our crops, you can also check specs and handling notes here: View our products.