If your windscreen and footwell vents always blow hot air then check the hot water valve, wiring harness and A/C control module. If the water valve is identified as faulty, then read on.

It happened not to find a brand new water valve but at OLE Jordan, and the cost of it is approx. as same as a used car in jordan!!! and to avoid buying a second hand one (which may do the same after a while), I decided to fix it myself..

Below are the instructions (valid for BMW e38, 1999, 740iA with 4.4 Ltr Engine V8)

Remove the water (Heater) Valve as shown below:

Once the water valve has been removed from the car, undo the six screws holding the upper part of the valve to the rest of the valve/aux pump frame.

In my case one of the water valve solenoids went into open circuit. In the following I will describe how I managed to fix the problem. I was lucky because the solenoid coil wire corroded away in a place that I could access. However, with a bit of patience it should even be possible to completely re-wind the coil, if necessary.

With the screws out, lift off the upper part of the valve body. As the next step, detach the faulty solenoid with its housing by pulling it sideways away from the plastic frame with the connectors. The fork shaped contacts to the little windings should slide off; in my case I actually had to apply a fair bit of force.

Lift out the faulty solenoid from its housing, once removed from its housing, it was obvious where the solenoid winding became corroded with the broken wire clearly visible:

Remove the little winding from the contact pin and extend the broken wire by soldering a short length of similar wire to its end:

Finally, remove and clean the plungers and seals, then reassemble in reverse order.

I also smeared a little silicone sealant on the mating surfaces to prevent any leaks.

Before fitting the valve in the car, it might be an idea to test it on the bench by applying 12V to pins 1-2 and 1-3, and listening to the clicks of the plungers.