andy boardman

Evening all

I have an 87 euro with a peculiar problem - I have recently replaced the freeze sensor in the unit and had lovely modulating cold air of a constant 5 degrees and the ability to vary the temp between max cold 18 and comfortable 24 degrees (it used to ice up the unit in the dash until I did this) - I have now lost this - I either have full cold when the slider is right over to max position or if moved away from the max cold position even a little bit I get top centre vent cool and bottom centre vent 50 degrees hot. This is not always consistent - sometimes I get full heat out of both vents and then other times I get the right temp across the scale. Moving the temp control slider does cause the solonoids to click. I have disabled the centre comb HVAC (has been for a long while)

Any ideas - I have seen a post in archives about a control unit under the dash over the accelerator .....I will look for that (bearing in mind mine is RHD) - is it more likely the control unit is on it's way out or solonoid unit??

All help appreciated as usual.

Regards..............Andy

dr bob

This is a symptom of a temp sensor loop that's been disturbed. There are three, one from the in-dash temp sensor, one from the exterior temp sensor in the alternator cooling duct, and one is the slider itself.

Start off by asking what you might have disturbed while working on something else.

-- The in-dash sensor has a little blower that draws air in across the temp element. To access the assembly, you get to pull the center dash section apart, and if I remember correctly you'll have the glove box apart for this, at least on the left-hand-drive US models.

-- The outside temp sensor for the climate control lives in the air duct to the alternator. Access to the sensor requires removal of the LF wheel. and then remove the front wheelhouse liner section. You'll see that the duct hose is formed up into an upside-down "U", with a metal coupling within which the temp sensor lives. The "U" and the sensor coupling are attached to front face (front is front of car) the wheelhouse liner with screws/bolts and some metal bracketry. Wiring for the sensor has a connector which can become corroded. If you are in there this far, pull the electrical connector apart and make sure the pins are clean before reassembling.

-- The temp slider is part of the in-dash control unit. You can remove the control unit by first removing the left-side console cover, the carpeted panel held in by a couple screws. Package tray may need to be at least loosened first. With that panel removed, you can see the back of the controller (towards the front of the car...) and the wiring connections that attach to it. Note the positions and types of the connectors. From the face of the console panel, remove the center vent assembly by pulling toward the rear of the car, and remove the "H"-shaped trim piece to see the screws that hold the control head. Remove the screws, and lift the control head out far enough to disconnect the fan wiring connector on the left side. The controller rotates out, right side first, before pulling it clear.

On the bench, disassemble the controller by removing the srews and lifting the tabs with a small screwdriver. Inside you'll see the slider. If there are obvious problems with the wiper and the traces on the circuit board, you can do some repairs. Be careful with the black fiber optic tubes as you work and when you reassemble. Installation is pretty much the reverse of disassembly as you put the console back together.


Be aware that there are ways to test the integrity of each loop from the wiring harness to the control head and the harness connections at the climate control brain. Do the ones at the control head first, since the wires run to both locations anyway. Procedure is in the WSM, uses an ohm meter
to test for ambient temp at the two sensors (they are thermistors, one is reverse-coefficient...) and at the slider. The electronic controller does nothing more than compare the loop resistance of the combined interior/exterior sensors with the slider resistance, and decide whether to operate the flaps or add heat based on that difference. No real magic going on in there at all.


Let me know if you need more detail on the test procedure. I'm sure I can scrounge some more if necessary. There may also be some writeups on this same subject on the Nichols tips page. Worth a look!

andy boardman

Thanks dr bob

I did some further digging yesterday and came to the same conclusion - I think that the control head will be the problem although I have not been "in" anywhere near it recently - perhaps I just have loose connections - I'll start there and see where I end up.

I'll keep you posted.

Thanks again........Andy

andy boardman

Morning

I had the control unit apart on the weekend and cleaned what could be cleaned - it would appear from testing that my temp mixing motor cycles the way you would expect it to as the slider on the control head is moved from full cold to hot but it appears to move too much too soon. At the 27 + mark small incremental adjustments up or down the scale result in the temp mixer motor making small adjustments as you would expect BUT it seems to already be up at the too hot end in the first place.

When full cold (micro switch at end of run in closed) then the temp mix motor is fully downwards - move it off this step a fraction and the motor cycle up to almost the horizontal - it bounces up a little at the end of the run and then setlles down a tad but it just seems to think that it should be allowing more hot air in than the slider should dictate.

I removed the little black rack that operates the unit that seemingly adjusts the resistance in the control head and made sure that on full cold the adjustment wheel on the potentiometer(? is that the right name for it?) was as fully closed as it should be - I then remounted the rack - that made some difference but still not enough.

I am therefore making the assumption that as per Dr Bob - the control head works OK BUT the resistance between the two sensors is wrong so the unit thinks it should make more heat than it should ?

I suppose to take this further I need to find an OHM meter...........to test the resitance in the sensors - if you think I'm heading wrong way please let me know!

All help gratefully received as usual.

Thanks.............Andy

bd0nalds0n

Dr. Bob:

I think I'm having the same problem. Both my internal and external temperature sensors work, in the sense that they provide some resistance and change as the temperature changes, however, when I activate my climate control, I get a full-on heater control valve, no matter where the slider is. I know I'm getting good vacuum, it's the solenoid that controls the heater control valve vacuum line that loses power when the control is switched on.

This makes me believe that the head believes that it's cooler in the car than it really is, and that the solution is more heat, no matter what the actual interior or exterior temperature.

It would be helpful to know what is the "proper" resistance levels at normal ambient temperatures (for southern CA, somewhere between 70 - 80 degrees); and,

It would also be helpful to know what pins on the semi-"ribbon" cable represent the interior and exterior loops.

This way I can determine whether the resistors are giving faulty readings, or whether there is a problem in the wiring itself.

If anyone else can chime in, it's definitely appreciated

Thanks in advance,
Brian

bd0nalds0n

Would it be a fair test to move the slider to the "24"c point, which approximates 75F deg, measure the resistance coming from the head unit, and use that as a rough approximation for what the internal and external sensors resistance should read, with the engine cool and windows rolled down, on a 75F day in So. CA? And any material differences would be attributed to a miscalibrated/failed sensors?

I'm trying to score a set of workshop manuals off Ebay, and got sniped at >$400....:-(

andy boardman

Evening

I have fixed my hot air con! - to recap - air con worked beautifully on full cold but gave heat / mixed heat / cold at vents in all other positions except full cold. Operating motor seems fine cycles up and down etc, all flappys working and control head is clean and seems to work BUT still the temp issue.

Bought a small multi-meter and went into the outside air temp sensor in front LH (from drivers seat) wing - used tip from archives to save removing inner wheel arch etc - and removed headlight cowl then headlight unit and then lowered units back into wing - hey presto! the offending connector. Pulled apart and it was seriously cruddy in there - could extract the two pins for the rubber shoe for cleaning but not the female parts - so cut it off and started again.

Measured 429 ohms at approx 18 degrees C.

Connected up and water proofed then started up and having sat in the late afternoon sun the air con went straight on and refused to budge off cool until slider was up to 27 degrees +. As the car cooled so the slider action started to work at lower temps.

A quick fix and cheap!!

Thanks for the help Dr Bob.

Regards................Andy