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2007 Mazda MPV AC Aircon Drain Blockage

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Summary

2007 Mazda MPV 2.3 Turbo

Noticed a couple of vehicle issues we thought initially were unrelated, and symptoms were weird, but working though them I eventually figured out what the issue was.

Issues

  1. There was quite a bit of water in the passenger footwell.
  2. There was water at the base sloshing around in one of the rear slider doors, we assumed it was rain related. There was some very heavy rain in the preceding days. This turned out to be coincidental.
  3. There was a very strange noise from the front – almost like a hand scraping down a washboard. Weirdly, the noise ONLY happened when either you turned right around a corner (nothing if turning left…), or sometimes when braking and reversing at any medium speed.
  4. The car had just been for a full service, which again was coincidental. I thought maybe a change of cabin filter was replaced at an angle that was hitting the internal fan or similar.

Investigating symptoms

After a few tests we found

  1. There was no noise at all when the internal fan/aircon was off. This showed that the noise was coming from one of the internal recirc cabin fans. Thankfully that ruled out more serious issues like aircon pumps, power steering etc.
  2. A taste (well a smell really) of the collected water showed that it wasn’t coolant (so not a heater core). This is one of the reasons initially I thought it may have been rain.
  3. With the Aircon on, I could see water dripping from the centre console, and there was no water dripping under the vehicle. Removing some of the internal trim reinforced this view, it was clear that the water was coming from around the internal heater/cooling core.

Conclusion

After the investigations, I figured out that the AC drain must have been blocked. With it blocked, there was a pile of water in the cabin filter/duct area. The water pooled in the cooling duct area and if turning a corner (to the right) the water must have been hitting the internal fan tips. The noise was the fan hitting the water.

The water in the back door was completely unrelated (and was rain). Each door has about 3 plastic drain holes, with little vinyl flaps on them. The flaps were gunked up, so a clean of these released probably a couple of hundred mls of water.

Cleaning the drain hole

The next step was to find the drain and clear it.

Car up on jack stands

The drain hole was pretty hard to find. I assumed it would come out of the firewall, but it turned out it was a bit further back and completely hidden by exhaust heat shielding. I ended up searching out the drain internally, and found where it exited. The usual googling found little info, and more comments about blocked cowling, rainwater etc (hence why I’m documenting online)

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I looked at poking some wire in, but the bends were too tight. I didn’t have an air compressor to hand, but a simple hand pump with a couple of squeezes worked well and water poured out. There was probably a few hundred mls in there and clearing this solved the issue.

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No more sloshie, no more noisy fan and the aircon worked a lot better.

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