964 - no hot air! Help.

elementsix · 10-30-2005, 03:11 AM

Belive me I have searched every thread on every notice board for 3 days and still can't find the answer. Read John 964 site and while very informative, only explains failed servos, which doesn't seem to fix my problem! The blower motor in the engine compartment is working - it does spin. There is major heat at the rear of the car leading me to suspect that flaps are not opening on the heat exchangers. The pipe to the blower motor is cold and the sensor (temperature I presume) on the top of that pipe was unplugged - could this be the problem? Replugging it made no difference (faulty?). I felt the pipes in the rear wheel-wells and they too are cold, leading me to believe that the hot air is not travelling up though the car. I suspect that the heat is going no further than the engine compartment.

Does the oil cooler play any role in the equation? Just a thought!

Any help greatly appreciated. Wife is giving me stick for buying a car with no heating/spending so much time in the garage!!!

Shane

plain fan · 10-30-2005, 09:40 AM

Okay, let me try to get you started by asking a few detailed questions:
1.) Rear blower mounted next to the engine. Are you 100% positive that it works when the car is running. You indicate that it "spins" but is it spinning under its own electrical power or are you physically spinning it.
2.) You mention "major heat at the rear of the car." Do you feel it especially around the rear wheel wells? The flapper boxes dump heat out right in front (direction of travel) of the rear wheels.
3.) Are you sure the flapper boxes hose is connected to the car? It is entirely possible that this hose is not in place. If this is the case then all hot air is dumped into the wheel wells.
4.) Don't discount the forward servos. The 964 flapper boxes work on air pressure differentials they are not mechanically controlled as in earlier 911s. The front air box, seen with the hood open directly behind the gas tank, contains 2 servos that controll the pressure in the heating pipes running to the flappers in the rear. When heat is desired, set by the thermostat, the servos open the flapper boxes and create a low pressure environment that opens the flapper boxes and draws heat into the cabin area.

You should be getting some heat, my rear blower motor is not working and I get heat just from the low pressure draw through the flapper boxes. Let me know if you need more assisstance.

elementsix · 10-30-2005, 10:54 AM

Are you 100% positive that it works when the car is running. You indicate that it "spins" but is it spinning under its own electrical power or are you physically spinning it.

Yes it definitely works - it blows when the temp is cranked-up.

2.) You mention "major heat at the rear of the car." Do you feel it especially around the rear wheel wells? Yes - I saw the flapper boxes and I think it is dumping the heat constantly. The flapper boxes dump heat out right in front (direction of travel) of the rear wheels.

Yes - I saw the flapper boxes and I think it is dumping the heat constantly.

3.) Are you sure the flapper boxes hose is connected to the car?
Yes definitely - I got under the car to check. All connections are fine, and it looks like there are pretty new heat exchangers.

It is entirely possible that this hose is not in place. If this is the case then all hot air is dumped into the wheel wells.

4.) Don't discount the forward servos. The 964 flapper boxes work on air pressure differentials they are not mechanically controlled as in earlier 911s. The front air box, seen with the hood open directly behind the gas tank, contains 2 servos that controll the pressure in the heating pipes running to the flappers in the rear. When heat is desired, set by the thermostat, the servos open the flapper boxes and create a low pressure environment that opens the flapper boxes and draws heat into the cabin area.

Hmmm. I presumed that the servos were a simple mechanical devise that opened flaps to allow the hot air into the system. One of the servos has been removed (quite simply missing!) The connecting ball-joint rod that connects to the servo-motor is also missing! See enclosed photo - it is number 2 that is missing (mine is a LHD like in the picture). With the car running, I manually pulled the flap-rod that the servo was connected to, but again no heat in the cabin. Servo 4 is present and working and as far as I can tell doing it's job - the arm rotates and pulls the flap to the open position.

Manually pulling the road should allow heat into the cabin - no? Or is it pressure related?

You should be getting some heat, my rear blower motor is not working and I get heat just from the low pressure draw through the flapper boxes. Let me know if you need more assisstance.

I really appreciate the help - thanks for the advice!

plain fan · 10-30-2005, 01:21 PM

Shane,
Set the temperature control switch to the blue dot and turn the ignition switch to the blue (cold) dot. Now get out of the car and look at the position of the servos. Now rotate the temperature switch to the red dot and note the position of the servos. If I remember correctly 2 and 4 should rotate. These are the servos that control the flapper boxes.

What happens when you set the temperature to full heat (red dot) and turn the fan onto either 3 or 4?

What happens when you set the temperature to full cold (bue dot) and turn the fan onto either 3 or 4? Does your car have a/c?

Since you mentioned that a servo is missing (2) it is quite possible that someone futzed up the settings for the servos.

elementsix · 10-30-2005, 11:29 PM

Hi Grady,

I did as you said above, setting the temperature firstly to cold - Servo 2 missing, so obviously no rotation - Servo 4 does not move - looks to be also faulty so the arm is fixed. That said, it is fixed in the 9 O' Clock position (see photo) with the gaiter fully extended - which indicates that the flap is open (stuck in the hot position) - but still no heat in the cabin!!

The car does have aircon, but this does not seem to be working.
Servos 1.3 and 5 are all fan motors and all seem to be working.

Is it possible that the previous owner, realising that the flap on the drivers side was stuck open, disconnected something else to stop the heating to the cabin?

elementsix · 10-31-2005, 03:10 AM

I just checked the heating again. All of the heat is dumping out of the heater boxes in the wheel-well. The heat is travelling no further than this point.

Question is this - do the servos in the front ONLY control the front flaps, or are do they control some flaps in the rear? I was told by one person that there is a differential control valve ahead of the blower which controls whether the heat is dumped out the rear wheel arches or continues up along the car. Could this valve be the problem? Is this valve controlled by the front servos. In other words does the servo firstly open the rear by-pass and then the front flaps?

It would seem practical to me that if you turn the heat down at the controls that the heat is stopped from coming up the car from the engine bay since if the heat stayed in the pipes running up along the car, the car would remain hot..

My suspicion is that this is where the problem lies!

plain fan · 10-31-2005, 12:24 PM

The differential control valve is the flapper box. The Porsche correct terminology is differential pressure valve; I used flapper box because you were using that terminology and I didn't want to confuse you. Let me think about the problem a bit...
Have you pulled the carpet bits from the footwells and looked at the hoses?

elementsix · 10-31-2005, 01:09 PM

Pulled the carpet on the passengers side - hairline slit in the flexible pipe, but pipes not heating-up. I've seen pictures of the valves inside the flapper boxes, but just don't know what controls them!

plain fan · 11-01-2005, 03:31 PM

The system works on air pressures. When cool air pressure coming from the front of the car is greater than the rear blower air pressure the flaps close and heat is vented. When the rear blower air pressure is greater than the front cool air pressure the flapper opens allowing heated air to pass forward into the car.

When you were beneath the car did you disconnect any of the hoses to see if the flapper inside the box moved freely? You can't easily check the passenger side one so I'd recommend the driver side for a check.

If it makes you feel any better Shane, my passenger side works rarely at best. Most of the time it allows hot air into the car but it stops at the front since the front ventilation is closed. Unfortunately the hot air just sits and superheats that side of the car. I think I have a leak in one of the hoses running to the flapper box on the passenger side but haven't investigated it fully.

I'd recommend the book by Adian Streather about the 964. The book has over 600 pages of information and photographs that will help you with repairs on the car. I got the book from this site.