Dictys

When I was troubleshooting the A/C and changing the control unit from full cold to full hot I would get no hot air and the engine would run rough for a minute or two.

As part of my A/C fix I was going to replace the heater valve which I started on today.

However, the heater valve was missing and the valve vacuum hose connected to the vacuum hose which runs under the left fuel rail cover to the front fuel damper.

Now if I want to restore the system to it's original setting where will the vacuum hose from the front fuel damper connect to?

It is not obvious from look at the engine bay or from the pet or workshop guides. I don't have a sticker on the hood either.

Thanks in advance.

StratfordShark

Model and year?

If the heater valve is missing then you must be getting very hot in Dubai!

If you can post a photo or two then it will be easier to guide you and make sure we're talking about the same parts.

the flyin' scotsman

What year is the car?

The newer cars have both fuel dampers and fuel regulator connected to a direct vacuum feed that comes from the throttle body under the intake.

The hot water valve is fed from the hvac solenoids under the centre console.

Dictys

Sorry missed it from my intial post 90 S4 LHD Japanese Spec

the flyin' scotsman

Attached vac and fuel line diag and descript:

Hilton

The dampners and pressure regulator all feed off a 7-way connector just next to the MAF on the LHD driver's side - its lying underneath the airbox. Some manual cars may also have a 5-way vacuum manifold there instead, but auto's and some manuals have the 7-way one, with one or more ports plugged.

Pic below is a manual '89 S4, with a 5-way connector.

GlenL

No heat? If there is no valve it should be getting heat. The (infernal) Porsche engineers made the fail state of the HVAC be to hot air defrost. Makes sense.

Old HVAC systems tend to get leaky and a good trick is to plumb a vacuum line directly to the valve. That's my suspicion of your no-heat problem.

I think you need to get in there and dig around. Identify the parts and be sure which vacuum hose is running where.

Jascd

Sounds like the heater valve line has been blocked off. Not sure why other than there being a vacuum leak that was meaning it ran hot all the time. The heater valve should definitely not be on the same circuit as the fuel dampers etc. Maybe that was why the valve was removed, - because of a prior wrong connection?

Mrmerlin

when you install the new heater control valve make sure to replace the short hose that connects it to the head outlet.
The vacuum hose that goes to the HCV is white

Dictys

Thanks for the responses.

The white vacuum hose (which should go to the heater valve runs to a black hoses which I have now established thanks to Malcom's wsm diagram runs into the foremost connection hidden behind the pipe on the five way junction shown in Hilton's photo above.

This according to the wsm this seems to run to the transmission. I suppose what I need to find is the where the black hose to the transmission exactly goes to next, as it is only about 10in long it obviously can't run straight to the transmission.

The heater valve has been replace by a small section of hose, I suspect once I have removed this section I will find one end plugged to prevent the flow of hot water.

Mrmerlin

the trans vacuum line is also connected to the 7 way vacuum T,
The trans line will usually snap so a new peice of flex hose and hard line should be installed to the metal line that runs along the top of the TT.
You may have to connect this from under the car and possibly remove the exhaust to get to the metal line.
also check at the trans for vacuum after you make this connection at the front .. The vacuum line is connected to the vacuum modulator on the left side of the transmission