Dim Clock and A/C LEDs

So the speedo, tacho, oil temp, fuel gauge, etc, are ok (and the instrument dimmer works properly)?

 

I would assume you have a bad connection in the HVAC ECU plug. I don't think there is a dim function on the LED's.
Simplest would be that the transparent windows/plastic are dirty. Worst would be internal bad soldering connections. But if you have some electronic knowledge you can open the HVAC ECU to check and redo the soldering. I did.

 

It's the knob on the tachometer.

@BBalto (?) Do you mean the LED displays or the lights in the buttons? Or both? The HVAC control panel receives a number of different voltages. One is a varying voltage from the instrument dimmer (HVAC panel yellow-red wire, pin 24). Another is a fixed 12volts (white wire, pin 26). Both voltages are supplied by fuse 5 in the passenger footwell. I don't know how the HVAC panel is wired internally so I don't know where these voltages go. I don't have a 348, so if you could let me know if the dimmer affects the faulty lights, this would help diagnose the problem.

 

And do they dim and increase in brightness using the tachometer knob?

If you have a digital multimeter/voltmeter, maybe we can check the voltages going to the HVAC panel and the earth for the panel. If the voltages and earth are ok, then we have to assume it's a faulty panel.

Sorry, I was a bit slow coming up to speed. I didn't realise the 348 clock was part of the HVAC panel and was digital. I assumed the 348 would be more "analog" than the F355 (It's actually the reverse).

 

Only where it counts kid. (steering, suspension, etc.)

Image Unavailable, Please Login

 

The digital displays (temp, clock and the bar display) are getting power from the electronic circuitry, i.e. the microchips, and are not directly connected to the power supply to the unit. If the bar display (middle), the illumination of the panel as well as the LED-s on the buttons are bright, then there is no problem with the power supply in which case the dimming of the two displays is most likely either due to them getting "tired" or due to a problem with their microchip drivers.

 

The power supply related pins on the yellow connector at the back of the AC ECU are (looking at the socket):

Image Unavailable, Please Login

 

Once again the electrical go to guy Miro to the rescue
Nice stuff

 

Disregard this.

Miro, do you know what pin 24 does on the HVAC panel?

The dimmer voltage goes to the vertical console on a yellow-red wire, so I assumed the yellow-red wire on the HVAC panel (pin 24) was dimmer voltage. However, I can't find a wiring path. The wiring comes to a dead end at pin 9 on connector 14.

 

Is there a possibility that the HVAC panel has a poor ground. That multi connector at the back has always been a headache for poor corroded connections. Try pulling the connector and spraying some electrical cleaner on both parts, replug. It has worked for me with various HVAC error codes.

 

Pin 24 obviously does nothing, not connected. Pin 26 (white wire) is shown to go to the rev counter, i.e. to the rheostat so the AC panel illumination is dimmed together with the dash instruments. I am certain about the Pin 26 and the white wire being for the AC panel illumination as, when I completely modified the electronics inside my AC ECU box, this white wire was one of the few links that I left unchanged.

 

Weird... On Fig 5, the white wire is shown going to one of the pins on plug G of the footpad relay panel. This is powered by fuse 5, so a constant voltage. The same fuse feeds the tacho potentiometer, but this is on the hot side (12v) of the potentiometer. A yellow-red wire comes out of the potentiometer to the dimmed instruments.

 

There appear to be two links from the dash gauges (the rheostat in the tacho) to the console - one regulated, this is the arrow at the fuse box on Fig. 5 pointing at 112 and another wire which is not regulated (looks like "B" for white) which goes to the connector 14 at the AC ECU diagram. I actually did not go into details (and Fig. 5 I have is not very clear at all) when I established that the white wire into the AC ECU is for its illumination, I just concluded based on the link to the tachometer that it must be linked to the tacho illumination (what else), i.e. to the general instrument illumination. It seems that the AC panel illumination is not dimmed and that the other wire (--> 112) is for dimming of the two gauges on the console. It makes sense as the AC panel illumination is by LED-s which would not dim all the way but just go off at certain level of reduced voltage/current. Until today, 6 years of 348 ownership, I never tried the dimmer to see what it does (but I new it existed!).

 

I too have the same phenomena but if I tap on the side of the console they get bright again I'm going to try unplugging the connector and cleaning with electronics cleaner as suggested I'm sure that's the problem. No problem at all with any of the functions adjust intermittent dim lighting.

 

It seems every 348 has problems with this system. My 1990 348 has issues sometimes temporarily rectified by a "smack" on the side of the console with my hand. I wish there was some common denominator after all these years. My car often has the fan on full speed when powered up and am unable to adjust with button controls. I have replaced the "hidden fuse" with a good quality aircraft circuit breaker and have removed the console hvac unit and carefully cleaned pins, etc etc..... Is it possible the main ground ( pin #2 ) is the common fault ? If anyone has any new ideas I would like to hear them. Thanks to all, JG Wesanko 1990 348 ts

 

PS, I halve also replaced the fan speed transistor unit in the fan plenum with no improvement. And they are Hard To Find......

 

A few years ago, I found a post on a forum (can't remember which) providing pictures showing how to access and clean the multi-pin connector(s) inside the unit:

Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login