You will crack the dash plastic trim if you try to take it apart since it is old and brittle. 1st determine where you are getting heat and where you are not. Are the floor vents providing heat, the defroster vents, the center vents or none at all? Read this first:

On the later model 944 HVAC systems, the A/C evaporator and heater core are contained in the same housing. Temperature control is automatic and is controlled by 3 temperature sensors. Once a temperature is selected it is maintained automatically by the temperature control unit repositioned dampers to control air flow through the unit. The temperature control unit determines how to position the dampers by comparing the signals from the three sensors. Once sensor senses outside air temperature. All air flow therefore passes through the A/C. From there it is either directed fhrough the heater core or bypassed the heater core (via a system of flappers) and into the cabin. Below are pictures of the late model 944 HVAC component locations.


On late model 944s (1985.5 and newer), there are several problems that can cause the full heat condition. The first and most common problem is a damper linkage in the driver's side footwell (for left-hand drive cars). Stick your head in the footwell and look up and toward the center console. You should see a small diameter metal rod which rests in a white plastic support and is held in place by a metal retaining clip. On later model 944s, there are two damper linkages instead of one and they are located behind a plastic cover. One of the plastic clips on the linkage may be broken preventing the linkage from operating the damper. When the damper fails to operate, the system fails to full heat. Most German cars are designed to fail this way. It's a safety feature to keep you from freezing in winter. The first picture below shows a linkage that has come loose from the support because the metal clip is broken. The second picture show the linkage properly in place with a new support and clip along with the part numbers for the support and clip.

thanks Curtis. Much appreciated.


MJ in Beirut

I'm not getting any heat at all but there is hot water getting there as the pipe going from the water pump to the dash is hot, when engine warms up. I will look for what you have described which sounds like a very basic linkage, right?

MJ

The pipe on the exhaust side of the engine is a return pipe, carrying water FROM the dash TO the water pump for recirculation.

The water TO the dash comes out of the back of the cylinder head, under the intake manifold (next to the oil filler cap).

Water can't flow through that pipe unless it is also flowing out of the head, through the heater core, and back out again.

is it possible i just have air in the system in the dash area?

absolutely. that is why when you bleed the system you have to have it fully warmed up, thermostat open, and heat on high with the heater fan on full.

Where do you bleed it, when it is hot and running? On the top of the engine where there are two small nuts (one an allan if i recall)? Which one, if so?

The bleed screw is a 12 mm located on the hard pipe elbow at the front of the engine head. I remember the odd size because I always grab a 13 mm wrench to bleed :rolleyes:

Update:
I have found the lever underneath the driver's side which was disconnected. But after moving it, i have discovered that this is just the flap to direct the air above or below. I couldn't find the second one which actually regulates the hot air (i suppose)

Also, after feeling the water pipe by the heater valve i noticed that it was only warm to touch. I'm wondering whether the heater valve is faulty, although fro what i read on Clarkes, when they are faulty they usually stick open (hot). Both the vacuum lines are attached. One goes to the emissions control valve near the fuse box and the second goes to the front of the manifold near the air intake rubber hose.

Any advice appreciated. It's getting cold here.

Oh, one other thing. Is it possible that my engine simply isnt getting hot ENOUGH for any heat to come through? It only manages to get above the FIRST marking, which i am told is not normal as it should be at least on the one third level.

thanks


MJ

To answer your question about if the engine is getting warm, the upper radiator hose connection to the engine should be too hot to touch (about 180F) when the car is warm.

Here are the links to Clarkes where the above info came from with pictures. Keep working on it!

Troubleshooting - Heating, Ventilation, and Air Conditioning (HVAC)

944 HVAC Operation and Malfunctions

I think you have answered the question for me. Mystery over. The upper hose is hot but a long way from being too hot to handle. I'm going to changet the thermostat to the hotter one (i have the 71 degree one)

i have those links. V useful. Thanks

MJ

MJ,

71C should be hot enough to get some heat. Can you actually move the lever on the heater valve? It could be stuck closed.

A problem with the heater control valve opening may also be caused by the vacuum solenoid valve going bad. Remove the solenoid and apply 12 VDC to valve to see if it opens and closes properly.

Also air in the cooling system could be a cause of too little or intermittent heat.

Intermittent Heat

If your car's heater works fine while driving down the road but the air from the vents becomes cold at idle, you probably have air in the coolant system. Air pockets in the coolant system often accumulate in the heater core. At higher engine RPMs the coolant pump will develop enough discharge head to force some coolant through the heater core. However, at idle, the air pocket will keep coolant from flowing through the core. If you are experiencing these symptoms, vent the coolant system using the COOL-02, Coolant System Draining, Filling, and Venting.

My ventilations system alternates between blowing hot and cold air. (Late Model 944s)

Possible Causes
Checks
Procedure
Typically this is caused by a dirty interior air temperature sensor. There is a small fan that supplies air flow to the interior air temperature sensor. It's located behind the small round vent next to the cigarette lighter. Underneath the dash follow that tube toward the firewill and you'll locate the interior temperature sensor. See pictures in HVAC-01 for sensor location.

It is not the type of heater valve which has that tiny lever. It is another type, i think.
But if i pull off the vacuum lines it should open completely right? And where is the vacuum solenoid valve?

MJ

Take another look at the valve, late car should have the plastic heater control valve like this on the left. I think you would see the lever move when you adjust the heat. When the engine is warmed up is it warm on both sides, it is open, if cold on one side it is close.

http://www.944s2.com/images/heatervalve.jpg

Look at the diagram on Clarkes link above for location of the solenoid valve, it is under the dash, right side...

Mine has two tiny vacuum lines going into it from the top. Perhaps someone fitted an aftermarket one. But that's what i have/
I will search for the switch but i stil feel in my guts that the whole system should be running hotter as there is a tiny, tiny amount of warm air which comes through. I might just pull the entire valve out and have a straight through system.

thanks

http://www.944time.com/porsche/image...trol-valve.jpg

This is definatly what i don't have. Is it possible that a previous owner removed it entirely, when an engine change was done (hot country here)?

All of those gizmos under the dash will only work right if you have the right HCV. If you don't have access to replacement parts to get the correct one, then maybe you can experiment with running vacuum lines directly to the valve and see if it opens up.

is there a diagram or article which explains exaclly where the vacuum lines go though?

PM me with a shipping address and I will send you a used one I have to try out.

Update. Still stuck. Have put a hotter thermostat in which im happier about as the engine is running more in line with normal operating temp, but still only cold air in the car. No change at all.