Heat transfer in plain language

Radiation

Sunlight crosses glass and heats the dash, seats and floor. Those surfaces then warm the air and radiate towardoccupants. Exterior covers work because they intercept much of that energy before it reaches the glass/interior.

Conduction

Solar-heated metal conducts toward the inside. Insulation adds resistance, but steel ribs, doors and uninsulatedcab panels become thermal bridges around it.

Convection and infiltration

Air movement can help or hurt. A fan blowing across skin improves comfort. But exhausting conditioned air oropening doors replaces cool dry air with hot humid air that the A/C must condition again.

Latent heat

In humid climates, the A/C must remove water vapor as well as lower temperature. That is why two days withthe same outdoor temperature can feel completely different and use different energy.

System rule

Do not judge a cooling upgrade at the vent. Judge it by the hottest occupied zone, humidity, energy usedand whether the system can recover that energy safely.

CHAPTER CHECK

• I can explain which heat path this step addresses.• I measured its effect at front, middle and rear - not only by touch.• I added its power, failure mode, maintenance and safety action to the system plan.