Difference between revisions of "Air Con Stuck On Windscreen"

Revision as of 04:03, 17 October 2007

rolnoer

Air Con Stuck On Windscreen

Background

My 1997 (December) Mondeo HC GL Sedan lost the ability to control the airflow direction in the cabin. It was stuck on the windscreeen.

A Ford Dealer had two goes at it and made the problem worse as you'll read later.

In a nutshell - there were two problems: The main vacuum feed connection from the engine (via the main blower unit) and the AC/Fan Speed switch on the dash fascia. What a nightmare.

Method

The first problem was actually an original problem that the Ford dealer made worse . . . the main vacuum feed comes into the cabin from a rubber L-shaped connector that sits right behind the cold air box, almost against the firewall - dead centre of the car. This vacuum line connects to the main blower box inside the cabin, right beside the clutch pedal(right-hand drive car).

There is a secondary vacuum connection right near that one that leads up to the blower controls on the dash facia. This secondary connection had a pretty marginal seal on my car.

The reduction in vacuum was just enough to stop the various vacuum slave cylinders from pulling-in and doing their job. Pushing this connector hard into place doubled the vacuum!

Here's my dig at the Ford Dealer . . . in their effort to fault find the problem, they cut this secondary lead and ran a piece of windscreen-washer tubing in its place. Some of you will already know the problems this will cause . . . the soft walls of that type of tube will collapse when any sort of vacuum runs through it and secondly, the internal diameter of this general purpose pipe was four times greater than the original hard-walled, small bore vacuum pipe. Guess what, the vacuum pressure drops by the same factor. Although in a closed system this is less of an issue, when there is a small leak . . . it's a big issue.

Once I'd reseated this secondary connection from the blower box (and doubled) the vacuum - the selector switch still wasn't working. Of course I had the whole console and fascia out and was getting a bit perplexed . . . after all it's a fairly straight-forward (if not a little complex) system of redirecting the vacuum to various slave cylinders.

I could hear a small leak near the control switches and by process of elimination I discovered that the vacuum was leaking at the AC/Fan Speed selector switch.

There's a small T-connector that links the Air Direction and AC/Fan Speed switches. Once I unplugged the vacuum connections to the AC/Fan Speed switch and blocked the main feed connection (the black hose) - Bingo! I restored full and reliable control of Air Direction within the cabin.

The downside in doing this is that you loose the ability to select Fresh/Recycled air (it defaults to Fresh Air) . . . but that's a small price to pay to have control again of where the air blows.

I'm still not clear whether it's the AC/Fan Speed switch or the vacuum connector block that feeds into the back of it. I guess I'll just have to buy a secondhand switch and try it. Replacing the vacuum connector block would be a much bigger job as the whole vacuum loom for that switch has to be replaced (no easy task).

As for the first problem - I'll probably use some silcon sealer to securely attach the secondary feed that comes from the blower box, near he clutch pedal.

As for the dodgy bit of tubing the Ford Dealer used . . . I'll have to see if there's a reliable method of joining vacuum hoses. In the mean time, while there's no other leaks - it's OK.

Submitted by Crusher in Australia