Recirculation flaps (heater)

[zcacogp]

Chaps,

Following on from my sudden escape of smoke I have dismantled and re-assembled the heater fan box on my S2. (Thread here: http://www.porscheclubgbforum.com/tm.asp?m=748811). Since reassembling it, I have noticed that the recirculation flaps don't move - they remain "open" all the time. I don't think this is related to the smoke.

I am struggling to learn more about how these work - they are run from a vacuum line, which T's to both of them, and neither work. They move freely when pushed by hand, but spring back when released.

How is the vacuum to power them generated? (I did re-attach the line, both the bit inside the box and the bit outside the box.) And what else could cause them to fail like this?

Thanks!


Oli.

 

[robdimond]

Oli,

This is all from memory from when I stripped everything to change my heater matrix...

The vacuum lines from the actuators go to a T piece. This then goes to a fitting in the bottom half of the fan housing which is actually a pipe straight through the fan housing (the means for crossing into the car interior). On the other side another rubber hose then goes to a solenoid valve in the drivers footwell on the side of the heater box. There are two solenoid valves here, one for the recirc flaps and one for the heater valve (that shuts off the water to the matrix). Both the vacuum supply and the line to the heater valve cross the bulkhead at the same point as the heater hoses.

What I would do is:

- First check the actuators are not broken, if you block the hose outlet with your finger you should feel the pressure... or you can use a brake vacuum bleeder if you have one to make sure they move
- Check that the heater disc valve is working by moving the temp from min to max while the engine is running. If this is OK, you have good vacuum supply going into the solenoids
- Assuming this is all OK, check that the hoses are all attached. It's very easy to take the fan bottom housing off and reseal it to the scuttle panel and forget to attach the hose... ask me how I know this! You may be able to see it looking up under the dash, or feel for it.

If all that looks OK, then maybe the solenoid is broken, or perhaps the electrical connection to it? I still have a spare solenoid I can send if that's the case.

I suspect it's the diaphragm in the actuators... the one in my heater disc valve was knackered which coupled with a broken heater clip causes the 'always on hot' scenario.

Rob

 

[zcacogp]

Rob,

Thanks for that detailed write-up. It's helpful. I've made it work, and it had failed for two reasons - firstly I had managed to trap the rubber vacuum hose to the actuators under the fan box when I re-attached it and also I had managed to pull the hose off the solenoid in the driver's footwell. Doubly annoying, but it all works as it should now.

Thanks very much for the offer of the spare solenoid, although I don't need it. However I'll happily settle for an explanation of how they work; what does the white cylindrical bit on them do?


Oli.

 

[robdimond]

Glad it's working. I have no idea what those white bits do, it confused me as well!