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.

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

Locate the hot water valve on the firewall in the engine compartment.


Unplug the valve connector (C-K).

Check that +12V is present on pin 1 of the connector (K). If not, check fuse and continuity of red/green wire from plug (K) to fuse.

On the valve itself (connector C) the resistance between pins 1 and 2 should be ~13 Ohms, between pins 1 and 3 again ~13 Ohms, and between pins 2 and 3 ~26 Ohms. By applying 12V on pins 1 (+) and 2 (-) you should feel and hear the valve operate (close). Same should happen for the other half: pins 1 (+) and 3 (-). Each half of the valve should draw ~1 A current. Applying the voltage should stop the windscreen and footwell vents from blowing hot air.

If the valve does not operate as expected also remove connector P from the aux. water pump. Disconnect the three water hoses (H). Carefully lift the guides (G) out of their rubber mounts and remove the  valve assembly. It may be possible to clean and fix the old valve (some people had success with this), if not replace valve assembly (BMW P/N 64 11 8 374 994). If you had to remove the valve assembly, remember to top up with coolant and bleed the cooling system.

If the valve checked out OK, take a look at the control module end:

Pull out one of the switches in the centre console.

Reach in through the hole and push the A/C control module out slightly. Grab the module and pull it out.

Locate the blue connector and pull it out by lifting the white handle.


Press in small white catch and pull off blue connector housing.


Check continuity for yellow/purple and yellow/brown wires between connector and hot water valve. You should also be able to operate the valves by connecting these two wires to ground. The connections should draw ~1A current each.

If these fail, then take a closer look at the wiring harness.

Otherwise plug the white block back on the control module making sure that you get the orientation right. Check that on these two pins there is (with reference to ground) +12V when highest temperature is selected, and less than 0.5V when temperature is set to the coldest. If you find significantly different values, then the control module is probably faulty.

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