Wet conditions cause heat to come on full blast

Question

Our 2006 Honda Odyssey minivan has a weird behavior with the climate control. When it is very wet, the heat only comes out at full blast when turned on, regardless of what the temperature is set to.

I've only ever found this to happen driving on the highway in the rain. It seems to happen after about five minutes after driving in conditions where there is tons of spray totally soaking the car. Today I was driving half an hour on the highway in such conditions and this happened.

When this happens, I can turn the heat on for five minutes at full blast until I get to hot, then I turn it off for five minutes until I get too cold. If I turn the temperature controls all the way to "low", then it blows cold air. If I turn it up even one degree (I think to 58), it seems to turn the heat on fully.

I often have the defroster on in these conditions to keep the windows free of fog, and I had thought it might be related to that setting. But today, I had the climate control set to "auto" when it happened, not on the windshield.

The problem persists until the car has had the chance to completely dry out in the garage overnight.

What could be causing this?

Answer 1

My guess is that the ACC temperature sensor is getting wet, confusing it into thinking the interior is colder than it really is.

If you have an "interior temp" reading on your dash, it probably uses the same sensor. See that it shows about 58 when wet and normal temperature when dry.

If that's the case... find the sensor! If you don't have a service manual, google might help you figure out where it is. Chances are, it has water leaking onto it. Maybe you can put a little cocktail umbrella over it. :)