Odd cabin air temp sensor actvity

SteveV70 · Post by **SteveV70** » 22 Dec 2022, 11:10

Hey there,

Been working on the A/C and fixed the most glaring problem,…the reshimming to spec the compressor clutch.
It clutches up now and seems to be working ok.

Next problem is that the air coming out is not cold enough. It’s making cold, but it’s not delivering it well enough to the cabin.

I investigated and found that the cabin air temp sensor thermistor was broken. I fixed it by soldering in another new thermistor of the proper resistance value.
Air is still not working well enough. Also,…one side is colder the other side is warmer.

Online investigations lead me to believe there is still something wrong with the Thermistor as these type issues are related to this many have found.

The main REALLY WEIRD thing I’ve found is that the little fan in behind the thermistor is running,…all the time.
And by all the time, I really mean all the time… even with ignition off, key out, door shut.
It’s just there humming along quietly. Dunno what that little thermistor bulb would have to do with making this fan run continuously.

I have the DICE and also a dedicated laptop with the VIDA and ran the diagnostics on it.
It said the sensor (the one in question) is at fault, signal resistance too high and/or no signal.

Fair enough, I’d say,…but my question is what in the heck would keep that little fan just keep running all the time?
I’m contemplating just getting another complete fan/thermistor unit,…but wanted to see what others may think about this.

2007 V70 Non turbo, 5 speed manual

(I’m very new to the VIDA program and was able to do the basic diagnostic test, but haven’t been able to get to the “recalibrating” and/or resetting mode to see if recalibrating the CCM would help. I need to work with it some more, but it’s not especially user friendly or self explanatory where that function is)

Anyone else run across this issue where the cabin air temp sensor fan runs continuously?

Post by **vtl** » 22 Dec 2022, 11:46

You need this: https://www.fcpeuro.com/products/volvo- ... or-8623354

SteveV70 · Post by **SteveV70** » 22 Dec 2022, 12:29

I’ve already verified visually that the blend doors are working. I got up under there and actually watched both of them as they moved from full stop in one position to the opposite stop in the other. I had read about the possibility of broken door arms, and/or motors going out.

Those both are working fine.

Post by **vtl** » 22 Dec 2022, 12:34

These actuators start skipping steps, the blend door is not going into the right position. When it starts, you can calibrate CCM and have it fixed for some time, but it gets worse.

SteveV70 · Post by **SteveV70** » 22 Dec 2022, 12:36

I’ve already verified visually that the blend doors are working. I got up under there and actually watched both of them as they moved from full stop in one position to the opposite stop in the other. I had read about the possibility of broken door arms, and/or motors going out.

Those both are working fine.

SteveV70 · Post by **SteveV70** » 22 Dec 2022, 12:39

I guess what I mean, is that when I call for full cold, both go to their stops in that direction.
Calling for full heat, they go tot he full stop in that direction.

I’m going to have to fiddle around with the VIDA computer a bit to find out where the “reprogramming” and/or “recalibrating” links are. I wish there were step by step real time instructions somewhere I could follow.
The fellow who sold me the laptop, vida, and DICE has a very useful and informative run down on how to get started and do the basic check,…but after that It’s all just use by learning I guess.

SteveV70 · Post by **SteveV70** » 22 Dec 2022, 12:50

AHA !!! I figured it out.
Did some sleuthing here on this site and also online and It seems that the little fan runs all the time when the car is “awake”,…meaning, as soon as you open a door it comes on.

I experimented by downing a window and leaving it for a half hour.
Came back and stuck my head inside,…no motor running.
Cracked the door a bit and motor starts.
Ok,…so mystery solved.

I’ve also heard that you’ve got to have the key in position 2 when you pull the battery to get the CMU out in order to change the thermistor. I did not do that. The thinking is that sometimes the little surge of spark when you either disconnect or connect the battery can damage the thermistor.

Soooo,….another one is on the way and I’ll try it that way next time.
Just for kicks i’m gonna put an ohm meter on the one I take out when the new one gets here and see what it reads. If it’s open,…..I may be on the right track.