Heater control not working - any tips?

[MiniNinjaRob]

Hi - my 940 has ECC and everything is working fine. AC is fine, blower motor is fine, temp sensing is fine but the control to direct where the air flow goes doesn't appear to do anything. I can't hear any noises when I move the switch around.
When I change the blower speed that works ok, when I change the temperature thats fine also, also the recirc and AC buttons work fine. Fuses have been checked and they are fine, pulled fuse 1 just in case and made no difference.
Any ideas what to do next?

BTW car has just passed its 4th MOT with no advisories and will be up for sale soon!!

[Chooch84]

I'm not 100% sure about the ECC, but it may have vacuum pipes running to the back of the ECC which control the bellows that direct the air around the vents. Might be worth checking the vacuum pipe from the engine bay going into the cabin.

[MiniNinjaRob]

Originally Posted by Chooch84

I'm not 100% sure about the ECC, but it may have vacuum pipes running to the back of the ECC which control the bellows that direct the air around the vents. Might be worth checking the vacuum pipe from the engine bay going into the cabin.

Where will that be? A picture would be great to show me if you can.

[Chooch84]

Here's 3.

Pipe from manifold


Leads to a convoluted tube


Leads to the bulkhead/dashpanel

[MiniNinjaRob]

Brilliant, thanks, I’ll check it out.

Come to think of it I haven’t heard the whooshing noises behind the vents recently so maybe it’s lack of vacuum that’s the issue. Hopefully!

[Laird Scooby]

If the temp change and recirc buttons are working, you have vacuum to the system. You'll need to remove the glovebox and under dash trim :





Then find that little beastie. Unplug and remove it. Inspect the solder joints :





That was the worst on mine although there were 3 dry joints, service the solder joints, refit and test.

That box has several vacuum solenoid valves, when they get the electrical signal from the control panel, they open the solenoid valve to allow vacuum to move the flaps for air direction, temperature and so on. You won't get the hissing noise if they don't work.

[MiniNinjaRob]

Thanks very much - electronics I can do easily! I’ll check all of the above and let you know how I get on.

[Laird Scooby]

Originally Posted by MiniNinjaRob

Thanks very much - electronics I can do easily! I’ll check all of the above and let you know how I get on.

Fingers crossed that's the problem - also worth renewing the NRVs if you have them, mine failed and under acceleration i'd lose all heater outputs and it would go hot!

[MiniNinjaRob]

NRVs? What are those?

[MiniNinjaRob]

Ok I took the circuit board out, there was one slightly suspect joint in the same place you had one (not as bad though). I have reflowed almost all the solder joints to make sure - time to slot back in and see what happens!!