Acu control module

[Smithy111]

Ok another unusual question, can anyone tell me how the acu control module in the dash work as my ac switch does not send 12v round to the fan relay i get a blip of power to the relay and the fans twitch as I turn the knob off, it looks like it been bodged in the past and how many wires should come off the control knob? Lols like 4 from wiring diagram.

also how the hell do you get the heater and flap control knobs off to remove the graphic panel? I’m getting seriously miffed at the design and construction of this car even for lotus standards.

[markt]

Post up a photo of your control panel, but there should be a tiny flathead  screw on the side of the small round fan knob, unscrew and pull off.

For the larger rotary dials for temperature, there's something similar on the sides which you need to press with a small jewellers  screw driver to release, then they should just pull off. Couple of screws behind where the knobs went attaches the graphics panel, and that's simple enough to remove.

All in theory - mine where epoxied on by a PO at one stage, so first time I needed to get to the panel, I  had to use brute force and break 'em off. New graphics panel and knobs tidied that up quite nicely.

[Smithy111]

Here’s the module removed, the control knob is just an on/off switch not variable so must just look at the thermistor from air through evaporator and turn the compressor on/off as necessary? Now what I would need to know is the resistance reading at ambient air of said thermistor as this is a very simple switch circuit. Also if faulty could the whole hing be bypassed so the knob switches the compressor on and off?

 

/edit I’ve just linked out the thermistor plug and applied 12vdc on the ground and red and it now switches power to the green as it should do if I’m. Or mistaken? So suspect the thermistor is faulty?

Edited August 17, 2019 by Smithy111

[fjmuurling]

it looks like the potentiometer is broken off from the left side of the pcb (where the blue wire runs over the horseshoe shaped thing).

[Smithy111]

The blue and brown wire were just bits I made up to test the pcb. I believe the potentiometer is not original as it only switches on and off so it’s been bodged up at some point in the past. Looking at replacing the whole control unit now

[Smithy111]

Just an update to this thread for anyone having similar problems with the electrical side of the a/c system these seem to break a lot in the same way.

Ive repaired my acu control unit completely for less than £5! Bought a new correct resistance range and type  potentiometer and led and repaired the pcb and housed it in a junction box. Now operates the compressor clutch and fans and have a working led. Now just to see if it will hold gas (I’m not confident in this!)