| It's too hot in here. Climate control problems. | |
Whilst returning from up North recently, a 250 mile journey, I noticed that I was getting progressively hotter despite turning down the temperature. The trim panel (‘floor console extension’ from the WM) near my left leg was hot to touch. No smells so I didn’t think the car was on fire. Pulled on the drive and on extracting the ignition key noticed the blade was uncomfortably hot to touch.
Quite glad there wasn’t a pile of ash on the drive the next day. Tried to replicate the problem but didn’t have time to drive around for an hour. Did take the trim panel off but could see nothing obvious. No fault codes on GAP IID, usual ‘clutch compressor off’ but it wasn’t.
A few days later I dug around the forum and the WM then went for a drive. When fully warmed up started playing with the heater. Found that I could increase and decrease the cabin temperature by using the extreme settings. Concluded that the coolant valves were working (replaced last year). Using the face vents managed to determine that the passenger side was performing as instructed but the drivers side was ‘lazy’ and generally hotter. I suspected a sensor fault.
Back on the drive I got the kitchen thermometer and checked the temps at the face level outlets.
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With standard settings, 22 on both temp settings and the wheel on hot you can see I was getting 56°C at the drivers vent.
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Moving the wheel to full blue had a dramatic effect on the drivers side. Passenger side was behaving normally.
Back to the WM and the Control Panel for the ATC (Climate control).
‘Inputs
The system receives ambient temperature, engine coolant temperature, engine speed and vehicle speed inputs in K bus messages from the instrument cluster. If the K bus messages are missing or faulty, the ATC module adopts the following default values: (standard values). If a fault develops in the input from the temperature selector switch on the control panel, the ATC module adopts a default value of 22 °C (72 °F).’
No faults on the instrument cluster and all looks normal.
IN-VEHICLE TEMPERATURE SENSOR – This is in the control panel behind a little grill. I had had control box out about 6 months ago when the air con seemed to be playing up. Dismantled and miffed to find no dust, debris etc. A disappointingly clean unit. I didn’t think it would be that and it defaults to 20 °C.
REFRIGERANT PRESSURE SENSOR disengages the air con clutch if there’s a problem.
EVAPORATOR TEMPERATURE SENSOR defaults to 32°C if there’s a fault.
HEATER TEMPERATURE SENSOR defaults to 55 °C (131 °F). That could be the problem but where is it.
After looking at myriad line drawings with vague arrows and nothing in the WM about replacement - ‘Two sensors are installed, one each side of the vehicle center-line.’ Brilliant.
Indebted to Highroller who actually took his out and provided a photo.It’s such a relief when someone has been there before and documented it (hence why I’m doing this).
Removed the floor console extensions and pulled the climate control assembly out. Removing the 5 block connectors was a pain but gets the unit out of the way.
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The heater temperature sensors are attached to the two white block connectors either side of the vehicle center line. Removal of those was fiddly and it’s not obvious how the sensors come out. From Highrollers picture the opening is circular with a cut out. Thought it would be the usual 90 or 180 ° turn to release. Nope, straight pull, a little bit tight but fine. I marked the left one with masking tape so I wouldn’t get confused.
Nothing obviously wrong with either one. They are NTC Thermistors and from what I’ve read are supplied with a constant current, as they heat up their resistance changes and this is used to control other bits of kit. I set up a test rig. Don’t judge, its freezing out there and the Mrs wants the windows cleaned.
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Multimeter on Ohms, kitchen thermometer, I used a hair drier to provide heat and noted the results.
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This appears to show that the right sensor loses resistance rapidly between 20 and 30 but is not a million miles away at the higher temperatures. I thought I would get a much greater discrepancy or the right one would be completely foobarred. I suppose it’s usual working range is between 15 ° and 28 °, so the upper temps shouldn’t matter. This being the case my multimeter is not sensitive enough to really show accurate results in that range. I also concluded that the kitchen thermometer does not react quick enough to the heat from the hairdryer.
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Changed the setup. I used a water bath (wifes favorite cereal bowl) ice and hot water from the kettle. Taped the thermometer to the side with the probe in the bottom of the bowl, could then position the sensor head directly over it. This was a much slower but far more controllable method. Started with cold water and a couple of ice cubes, removing them when the temp got down to 10 °. Took a reading and added hot water. Found I could slowly bring the temperature up, and back down, to get accurate measurements.
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Aaaargh. This shows they are both performing the same. Are they both broken now? If not then is the issue in the control module? Or is it something else entirely.
I’ve ordered a used sensor from ebay - £18 instead of £90 if you can find one. I may be chasing my tail because this is obviously an intermittent fault – air con problems in the summer, then performed fine, now heater problems.
Meanwhile I’ll swap them over on replacement and see if the wife gets cooked.
I read more of the WM than is probably healthy! Also saw that the ATC (Climate control box) controls the heated washer jets. Driving on the A702 from Edinburgh to the A74 in January the outside temp got down to -5 ° and my washers froze. With salt all over the screen and a low sun it was not good. Flask of hot water sorted them out and they haven’t been tested since. Control module problem? Earth issue? Gremlins?
Ebay sensor arrived and I retested all the sensors. Used excel and my very basic skills with it to produce a graph.
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Dark blue line is temperature, dotted lines are the sensors.
All performed pretty much the same!
Changed the blower motor and FSR. Thats a very small, sentence for a bit of a job. Blower started squeeking last year which I treated with a squirt of oil through the plenum. I bought another one which has sat on the bench ever since.
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I wrote all that several weeks ago then life got in the way and more motorway trips.
To my delight the new fan has an electric squeal, like a dog whistle, hoping it will go away with wear.
Although the fan appeared to be working it seemed sluggish so I changed the FSR to the old one. In doing so and whilst forcing my hand into that narrow gap, the rear fan burst into life at full bore??? The dial was turned right down and fan still running, pulled the fuse in the rear fuse box and it turned off.
Latest motorway trip – rear heater area was extremely hot to touch. I could control the heat in the front a bit by setting temp very low, wheel on blue and after a while cooler air would flow, the bolster also cooled down. Get too cold, tried minor adjustments but only big movements worked. Couldn’t balance it at all.
I think the heater control valve is working, perhaps not brilliantly, because I can cool down the front.
I'm very confused about the rear which seemed to happen when I was replacing the FSR. Is the wiring in that area related to the rear blower?
If the heater control valve sends coolant to each side, where does the rear get coolant from?
Can anyone tell me where the earth point (K108 I think) is located? It seems to be the earth for most of the units in the dash. Can't see it in the WM.
I'm suspecting the control unit. A couple of weeks ago I noticed the night lights surrounding the knobs etc weren't working. They are now. Also the switch to control the rear heating didn't light up. It does now.
Any help much appreciated. 2007 3.6 TDV8
1979 Mini Special
1988 Yamaha FJ1200
!952 BSA Gold Flash
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21st Mar 2025 12:47am
