Howdy,
I'm trying to fix the heat/AC system on my friend's 93 850. The ECC module seems completely dead. The recirculate and AC LEDs aren't coming on. The fan is going at high speed and the fan speed slider has no effect. The vent controls also don't seem to be having an effect either.

I tried the routine for getting the DTCs but it doesn't seem to be working. No codes are showing up. Not even the 1-1-1 everything-is-ok code. I'm nearly certain that the ECC is the problem but I thought I'd check with you guys since I don't ever do work on Volvos. Has anybody had to replace the ECC before?

Also, in the service manual when it talks about replacing the ECC it wants you to discharge the AC and disconnect the evaporator and various other things. What's the deal with that? I was under the impression that the ECC is a fully electronic module and that all you'd need to do is disconnect electrical stuff.

Thanks,
JR

Sorry i am not very familiar with the ECC system.

However, you may want to research the forum for that, it has been covered in quite detail in the past.

Cheers.

These symptoms could be caused by a number of things.

Generally speaking, if the A/C and recirc lights aren't flashing then you are off to a good start.

The fan having one speed only could be due to the fan control resistor pack being faulty (e.g. burnt out).

The various cabin vent shutter control motors re-act to the numerous temperature sensors situated in strategic locations within the air ducts and cabin and shutter motors are notorious for jamming or getting out of adjustment.

I don't know what you can do about the DTC because when it is working it supplies a comprehensive list of A/C faults (i.e. if the faults exist).

Did you check to establish if the DTC is functioning on other diagnostic modes such as ignition, fuel etc, because it might just be possible the DTC is faulty.

The ECC control unit is a stand-alone unit fitted into the dashboard, and can be easily removed if (1) the radio is first removed (to gain access to the ECC control unit locking pins) and (2), the wiring connectors at the rear of the ECC control unit are separated/disconnected.

The Haynes manual does not appear to distinguish between the fundamental components of the A/C system (i.e. refrigerant, compressor, condensor, evaporator, etc ), input/control devices (temp. sensors, pressure switches, A/C relay) and output devices (shuttermotors, automatic fan speed, two speed engine cooling fan etc.).

The stand alone ECC control unit helps co-ordinate all these various input/output devices together via the engine management unit EMU.

Sounds complicated - but it really isn't and I hope the information I've supplied is not too difficult to understand.

BOL.