rb95gs

Recently my '05 RL's automatic climate control system has gone goofy. I drive it infrequently and on short runs so I'm not sure how long its been misbehaving. I've noticed the cabin seems to warm up inside normally at first - but then turns gradually cooler and cooler until only cold air is coming out the dash air outlets. Raising the temp setting helps for a while, but the slow march to no heat continues.

Its been a real head scratcher. I have imagined maybe the under-hood hot water valve's stem is broken inside, or some other obscure cause.

But today on a longer run I noticed that with actual outside temp around 40, the cluster gauge was showing an outside temperature of 131 F ! That has to be a clue ! I was able to keep the cabin at around 70 by going into manual mode and turning a/c off, then running both temp slide on Hi, and the fan on low.

Looking on page 21-66 of the RL shop manual, the sensor's resistance-vs-temperature curve goes down as temp goes up, starting at 11k ohms at 14 degrees, dropping to 1k ohms at 104 degrees. An indicated outside temperature of 131 degrees would mean a near-shorted sensor. I've ordered a new sensor - but I'd like to know what else might be going on.

At the least I'll put a tester on the sensor. I also have an '08 MDX that just shows ----. Just lucky I guess.

Any thoughts?

rb95gs

So I unplugged the outside temperature sensor. Even cold Its resistance was only 370 ohms, where it should have been around 5k ohms. The rest of the system had just been doing its best to keep up with what it thought was a Death Valley heat wave outside. With no outside sensor installed cabin temperatures are back near where they should be. Thanks to the 50 readers of the first post - I'll post the results of putting in the new sensor when it comes.

Then maybe I'll look into why my MDX shows outside temp as - - - -. I had replaced that sensor too, but no joy at the dash yet. Its climate control seems not affected much if at all.

rb95gs

The new sensor arrived today and it appears to work perfectly. The indicated outside temp at the dash reads correctly - and the climate control system has returned to normal heating and cooling per all its settings.

The new sensor's resistance reading out of the box was around 3k ohms (shop in '50s) - and it plugged right in and worked. It's accessible in the RL's lower grille with no disassembly needed. Instead of the original equipment one for $42 I went with the $14 one from Jaff Bezos. (even comes with the receptacle and short wires).

I see there's still a bit of interest here - so Maybe I'll get into what's ailing the MDX and report back.

Happy holidays all - rb95gs