AU3 Fairmont: Hissing sound from climate control display

[rowan194]

There is a vaccuum tube behind a small vent at the top left of the clock. Today it started audibly hissing, the level changing with engine load.

With the message display centre removed I can put my fingertip on the tube and it will stick within a couple of seconds so it has decent suction. Maybe TOO much suction, like there's a vac pipe blocked somewhere else?

Since the hissing started this has also happened:

- Twice the transmission held first longer than normal, and when it did change to second it was quite hard.
- Once the trans/diff did a 'clunk' when pulling up to a stop.

But apart from that:

- Engine is idling fine. No surging, no stalling, no RPM wandering aimlessly.
- Power and response seems to be normal.
- No obvious vac leaks within the engine bay.
- Transmission only played up the 3 times out of a couple of hundred gear changes. Could be coincidence.

Any ideas why this tube has suddenly started making some noise? (Note it is actually a tube inside the MDC, nothing to do with the climate control actuators further inside the dash)

[mif73]

I don't think I can recall any vacuum lines to the MDC /climate control unit, but I do know that a lot of temperature sensors in climate control units work by sampling the cabin air with a small fan or vacuum pump which draws air past a temp sensor.

Are you sure the noise isn't caused by a noisy suction fan/pump in the MDC?

[mif73]

Well i just pulled out my mdc and guess what? There is a vac line plugged into it.
It looks like it is there to draw air over the cabin temp sensor thermistor.


I unplugged the fitting and there is a black filter type material on the end of the hose.

[rowan194]

Originally Posted by mif73

I unplugged the fitting and there is a black filter type material on the end of the hose.

At which end? When I unplugged the hose (MDC end) the end of the connector was just open. Maybe the filter helps reduce the noise and it's slipped through?

[mif73]

Originally Posted by rowan194

At which end? When I unplugged the hose (MDC end) the end of the connector was just open. Maybe the filter helps reduce the noise and it's slipped through?

The filter was on the hose end, not on the mdc fitting itself.

[rowan194]

Hmm... can you explain that a bit better? If you disconnect the hose from the MDC the filter is between the connector and the rubber hose? Still don't get it.

[mif73]

Originally Posted by rowan194

Hmm... can you explain that a bit better? If you disconnect the hose from the MDC the filter is between the connector and the rubber hose? Still don't get it.

The filter is actually stuffed inside the end of the hose about 10 to 20mm in (filter is not installed in the mdc itself).
I will see if i can take a pic tomorrow for you.