M44 Wiki


With this app: www.meditekst.nl/downloads/ACmod.zip you can modify a 607 (automatic gearbox) or 608 (manual gearbox) bin to work with the A/C system of a M4.3 car.

The advantages over the hardware mod described further on are:

  1. No hardware changes in the ECU or Car are necessary, in fact are undesirable.
  2. The ECU keeps full control over the A/C, as it should
  • When pressures in the A/C system are to low or to high the ECU wil turn the A/C off again
  • The clutch of the compreesor will not engage at high RPM, what could be destructive for the clutch
  • At WOT the A/C will be turned off giving you some extra HP for the road and saves your compressor
  • The radiator fan will only stay on when necessary.

WARNING: Don't use the softwaremod and the harware mod together !!

- Piet -


Inside the M4.4 ECU:

  1. Cut leads between ECU connector and circuit board for pins B6 (voltage after pressostat switch for compressor status indicator, M4.3 only), B25 (voltage from AC relay for M4.3, AC request for M4.4) and B40 (ground to activate AC relay).
  2. Solder a wire between the connector side of B40 and A13 (power ground,do NOT cut this lead, just solder to it) to enable the AC relay to be activated by the ECC module.  Leave the board side of B40 open, and press it down and out of the way.  This basically hard-wires the ground side of the AC relay.  Positive voltage is applied to the relay by the ECC module when the AC is turned on, engaging the relay, which in turn engages the AC compressor (assuming the pressostat hasn't opened, which cuts the compressor off to keep system pressure in check).
  3. Solder a resistor of a few kohms or so (I used 4.7k) between the connector side of B6 (which gets power from the compressor clutch) and the board side of B25 (ac request).  This causes AC request to go high when the compressor is on (actual power to the clutch), thus causing M4.4 to do idle correction when the compressor clutch is actually engaged.  Leave the board side of B6 unconnected (it is not used on M4.4).  Also leave the connector side of B25 unconnected.

Accessing some of these leads will require bending the other leads out of the way, as they are in three rows -- B40 and A13, on the bottom row, are most difficult to get at, but bending the other leads to the side (to make a hole in) allows access.  They're flexible, but do be gentle.  You will need a pair of snips with a fine tip, as well as a soldering iron with a fine tip.

Only issue is ECU has no control over A/C, so on hard accel it will stay on, but honestly i dont see that as a problem, because that was annoying anyway, plus when the AC is on the radiator fan will always stay on.