Footwell heater flap solenoid (servo) not operating

[zcacogp]

Chaps,

I'm looking for some more information on the operation of the solenoids (servos) that move the heating flaps to control airflow.

The issue I have is that the footwell flap isn't moving. With the ignition on, you can adjust the lower slider on the heater controls and nothing happens. Looking at the side of the HVAC unit in the passenger footwell you can see the solenoid and it doesn't move at all.

I've taken the solenoid out and cleaned it up - taken the motor core out and cleaned it up, polished the commutator and re-greased the gearbox and it works nicely if you apply +12v across the motor terminals. However I've re-installed it but it still doesn't work when you'd expect it to - i.e when you move the footwell heater slider. Where do I go from here with diagnostics? While I know that the motor in the solenoid works I don't know what the other connections to it do (there are five) so I can't test the whole solenoid, meaning it is possible that there is a fault in the solenoid or that it isn't getting the signal that it should from the HVAC unit. I have probed the terminals on the end of the wire to it and there are voltages across some of the terminals but I don't know what I am looking for so I can't be sure whether it works or not.

Does anyone else have any more information about these and how they should work? Or, failing that, does anyone have a spare solenoid they don't need which they could lend me for testing purposes?

For reference (although I don't think it makes any difference) it's an RHD S2, without air-con.

Thanks,


Oli.

 

[zcacogp]

More info: it's part 4 in this diagram.

Clarks Garage has good stuff about the way the system works but not enough detail about the signalling to be useful.

 

[zcacogp]

Update1: I can't make the picture in the above post work. Sorry chaps.

Update2: Problem solved. There are two diodes on the control board in the solenoid and, on testing, it seemed that one of them had failed open-circuit. Changed both of them (1N4007 swapped in to replace the obsolete SR1K4's) and it now works as it should. Well, not quite - it's quite sluggish, but it works. If anyone else finds this thread having had a similar problem then this is a simple fix.


Oli.

 

[bmnelsc]

Good work - and useful information. My '91 S2 is still operating properly? but regarding sluggish - the flaps are slow to respond to the control levers - certainly when compared to a cable connected system. You operate the lever and it takes a second - maybe two - before flaps start moving around and air flow changes. The initial change (after the car has set for a while) takes the longest and then once things have moved around it seems to respond more quickly although there is still some latency in the action.

 

[Waylander]

if you ever need one i have a spare heater controller, for testing, nice fix Oli