gst

what is the use of the back flap in the heater blower system which diverts hot engine air either to the vent on top of the rear grille or to the heater system?

What position is the flap in usually and when would the actuator come into action?

I am upgrading my early 993 heater blower system (with late model 964 blower with no vent to the back grille) to the one with the back flap/actuator. Do i need a new harness for that or there is already a plug in my existing harness for the back flap actuator??

Thanks in advance

Regards

gst

anyone in the know and is prepared to help?

epj993

If you're referring the the mixing valves that blend the engine heat into the cabin, those are located in the interior footwells in the 993. I believe they are the same units as the 964, but the 964 had them located up front with the rest of the HVAC (I think this is correct). Typical position is closed, until you adjust the CCU temp. Then they open based on your setting.

Is this answering your question?

gst

thanks epj993

i am not sure if we are talking about the same valve but your advice seems to make sense. The valve (993) i am referring to is located inside the black plastic tubing between the engine fan at the engine bay and the rear heat blower. There might be another valve inside the footwell i am not aware of. But it appears that if the valve is open, all the engine heat will be diverted to outside of the engine bay, whereas when the valve is closed, engine heat will go direct via the rear heat blower. I had a broken rear heat blower fan and had replaced it with the newer version with the valve/flap i referred to. The older euro 993 heater blower has "heart shape" tubing, but the newer version looks different with a valve/flap/vacuum actuator.

your help is appreicated

epj993

Unfortunately, I'm not familiar with that valve. I haven't done any work on the heater blower itself. I do know that when I was testing my broken valve in the footwell that it seemed to be charged with heat, that is when the valve opened heat came out immediately.

jkuniverse

I believe the rear blower functions in two different ways. 1. It blows heated air from the heat exchangers to the interior vents when the heater is turned on. 2. It draws cool air from the rear grill and blows down into the engine when a high engine temperature is detected after the engine has been turned off. I believe the valve you are referring to controls the opening/closing of the "heart shape" tubing, so that the air from the blower or the engine fan is directed to the correct area. I'm not expert in this area but it is my understanding of the blower and the valve. I hope it helps.

Ray Calvo

I don't know if this is what you mean, but there is a rubber hinged flapper valve at the botton of each heat exchanger that is intended to close when you put the car in reverse or drive over water. Otherwise, it vents "excessive hot air" (probably air not mixed with unheated air before being routed to the car interior).

Look for a book called "Service Information Technik '94"; is a great 993 model intro. (Porsche number WKD 498 621). Great source of such info.

gst

no, the valve i refer to is just next to the engine fan, inside the engine bay, and next to the rubber tubing

JasonAndreas

gst,
The fresh air intake system was not covered in the workshop manuals (at least for the first few printings, I can't find it in mine). The system might by documented in a September 1996 technical service bulletin "Heater Pipe (In Engine Compartment) - Revised".

gst

would anyone have a copy that can be emailed to me? i guess posting it up here may constitute an infringement of copyright