Continuous hissing sound coming from behind the heater in my 1.9 1998 Sharan Tdi

[londonphil]

Hi all,

I've owned the above vehicle from new but over the last 7-8 years, I've had cause to replace the heater control panel in order to cure the hissing sound which clearly comes from behind the panel. So far, that's meant 4 NEW heater control panels.

The problem appears to be coming from the lead which connects to the back of the panel and whilst the hissing sound is cured for a while when a new panel is fitted, it returns after a couple of months. I believe the lead may be connected in some way to the Turbo system but in truth, I just don't know although I now replace the panel myself having had such practice

There is clearly something amiss here, I really would like to sort it if at all possible.

Any ideas?

Regards

Phil

[Rob69]

Don't know about a hissing control panel lead but i've heard and had a few that his a bit when they've been low on refrigerant in the AC circuit. If it has one, have you had the AC system checked or regassed while all this hissing has been going on?

[londonphil]

Hi Rob, thanks for the reply.

No. In fact the AC has never been touched/re-gassed in 20 years and 34.000 miles.

The lead I speak of connects to the back of the heating control panel and aurally hisses until connected. As I say, it''s normally rectified by fitting a new panel but the last one lasted but a week so I think I need to look elsewhere for the problem. Phil

[Rob69]

It sounds like you have vacuum actuated heater control flaps, the system runs from vacuum created by the vac pump on the engine. Do you not mean a hose or tube rather than a lead? when you fit the new panels do you cut off the stretched end of the hose to fit onto the panel or do you just push back on the old stretched end of hose ?you possibly have a split or leaking hose connection or leaking vacuum operated actuator on a flap somewhere else in the system. That's dedicated ownership - 20 years!!
Here's a VW vacuum diagram, no idea what it is off but might give you an idea what is under the dash
http://www.cabby-info.com/images/HVAC/vacrouting.png