E38 A/C always hot from windscreen and footwell vents

I am not an expert, so take all information and instructions on this page with a pinch of salt. It is quite possible that they will harm you, your wallet, your car, or all three. If in any doubt at all, take your car to the professionals. You have been warned.

The pictures/instructions on this page are for a July '98 production date UK RHD 728i; if your car is a different model year, you may find that it is different from what is descibed here. Let me know if you think I should include references to these differences.

If your windscreen and footwell vents always blow hot air then check the hot water valve, wiring harness and A/C control module. Start with looking at my other page describing the initial diag steps for this problem. If the water valve is identified as faulty, then read on.

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.

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.


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:

Then wind the new wire on the contact pin:

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.

If you find any mistakes or want to suggest additional info that I should include, please e-mail me.