Erratic AC temperature on XJ12, 1992

XJ
41

I’d like to know myself. I’ve never seen that sensor or configuration. Must be unique to the very late V12 cars?

Cheers
DD

42

it measures…something… :smile:

I will see if anything will be different with AC when new installed and report.

Cheers,

Cene

43

**
It would seem odd, Cene - it’s very unlikely that both require the same inputs…

Varying the AC settings based on coolant temp would likely be a refinement if that was the intent - which, as Doug implies, is uncertain. It would be interesting to know how the sensor output varies with coolant temps…?

Frank
xj6 85 Sov Europe (UK/NZ)
**

44

Guys, just one more question…does in cabin sensor that is installed under the dashboard, have some vacuum line attached to?
I mean - there is a hole in the dash, through which the cabin air is measured by sensor. I guess there must be some, at least gentle, vacuum that actually draws the cabin air to sensor. If not, how the sensor measures the cabin temp without being affected by hot dashboard, when sun is shining on it whole day…

Thanks, Cene

45

There is a tube from the sensor attached to one of the main big air flow ducts. As air passes thru the duct a low pressure area is created which draws air across the sensor

The sensor and tubing can be viewed here:

image
image724×1024 82.8 KB

Cheers
DD

46

Another view can be seen here:

https://parts.jaguarlandroverclassic.com/parts/index/part/id/C06.C0659.C0659303.C06593035380/brand/jaguar/

Cheers
DD

47

Thanks Doug, but I guess you does not ”feel” anything if you close the hole on dash with finger, right? I was wondering if the line that you mentioned is loosened and the sensor is actually measuring the temperature of the dashboard…that could explain my ”complaints” over too cold AC especially on the sunny day that is not necesarry cold day, too.

Would that be possible?

Cheers, Cene

48

Just a couple of guesses.

  1. Low refrigerant. Causes hunting and adjustments on false data.

  2. low vacumn causes AC to go warm…Been there…

  3. Apply warm air to the sensor, how does the unit respond? Apply cold air, what does the AC do?

The sensor is a thermister. Corvairs used them to warn drivers of excess temperature…

49

Yes, if the tubing is disconnected you’ll get some mysterious symptoms. Been there, done that !

And, no won’t feel anything if you cover the hole with your finger. It’s a very slight drawing of air, just enough to make air pass across the sensor.

Cheers
DD

50

Thanks, guys. I will have to check that sensor, indeed.

Cheers, Cene

51

**
Blowing smoke at the aperture may show the flow, Doug…?

Frank
xj6 85 Sov Europe (UK/NZ)
**

52

Excellent idea

Cheers
DD

53

On the left air duct there should come out, right? For once bad habit of smoking will be of some use…:grinning:

Cene

54

A “good” cigar ??? Or a leaf not tabaco ???

55

After travelling that far it might not be visible.

Turn the blower to low speed. Blow a small puff of smoke towards the sensor hole. if you see the smoke travel into the hole, that’s as good as it gets !

Cheers
DD

56

Rothmans 100 S… but quitting. Well, I have to make some serious testing on my Jag, at least…:grinning::grinning:

57

Damn, i pushed the rubber inside the hole…:rage: Now the dashboard will have to go down, anyway.

58

Not that bad. Just undo the padded cap.

59

Yeah, I have found good video on that, not so complicated, really.

Cheers, Cene

60

Doug
I know the v12 series three is more your specialty, but I’ll take a chance your knowledge may solve the mystery on my XJ6, 1986. You can read the details on my previous post. Short version is as follows: Is it correct to postulate that the low pressure port on the air conditioning system on the '86 XJ6 is, in fact, situated on the pipe just behind the compressor? Thanks

Mel R.