When the OAT is below -16 C, how long do the inner zones heat before the outer zones start heating?

• A. 60 seconds
• B. 90 seconds
• C. 45 seconds
• D. 30 seconds

Answer: (B)

When outside air is very cold, the heating system uses a staged warm‑up so the areas closest to you come up to temperature first and the more distant/outer zones are brought in later. The inner zones are allowed to heat for a fixed period, then the outer zones begin heating. That fixed interval is 90 seconds, giving the inner zones enough time to reach a comfortable baseline before the outer zones start. Shorter intervals wouldn’t let the inner zones establish warmth properly, while longer delays would leave the cabin colder than desired for longer. So, the 90‑second inner-zone heat period before outer zones engage is the correct behavior in sub-16 C OAT.