Climate Control and AUTO Mode Guide

[Levenkay]

What does PTC mean?

Positive Temperature Coefficient (of electrical resistivity). Most heating elements DO have a PTC, increasing their electrical resistance as they get hotter, such as regular nichrome wire, for example. Plug an old-style radiant space heater in, and the elements run up to an equilibrium point where they glow red-hot. At that point, their electical resistance has risen enough to limit the current flowing through them and a balance is struck between the electrical power dissipated in the element and the heat power radiated to the room. The operating temperature is somewhat regulated in that if a breeze cools the element more than ususal, its resistance drops, allowing more current to flow, thus tending to raise the generated heat to compensate. The change in resistance per degree of temperature change isn't all that strong, though, so the temperature doesn't get regulated all that tightly against changes in heat extraction rate (you can blow on a space heater and visibly cool off the radiant elements).

The PTC elements referred to here are ones where this sort of thermal equilibrium point occurs at a much lower temperature, and the increase in resistance per degree of temperature change is more dramatic as well, so they tend to to a better job of thermally regulating their working temperature. They're made so that the fluid to be heated passes through them, or so I believe. When the PTC element and fluid are much cooler than the equilibrium temperature, the PTC's resistance falls way off, large amounts of current flow (subject to the power supply's capability, of course), and things get hot fast. When the element and fluid reach the point at which the PTC's resistance really starts shooting up, the current is choked off and the power consumed drops down. An elegant arrangement, and I always expected PTC air heaters to be very reliable, as they were chunks of engineered ceramic material, with not much to go wrong. How Nissan can have so much trouble with them in the LEAF's heater I can't understand.