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HEater not working 100%

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aporschefan

PCGB Member
Earlier this year I replaced the battery in my car as the old one was dying. During August/September, I didn't have a chance to drive my car for 3-4 consecutive weeks. When I next started the car, i had to use jump leads to get it going. Since then, I have noticed a couple of electrical problems.

Currently, the most annoying issue is the heater isn't working as it should. The fan setting 1,2 and 3 don't seem to be working. The fan does work in position 4 though. Also, despite the temperature setting being on the highest setting, the fan was blowing cool air for most my journey this evening. (Prior to the battery needing a jump start, the heater worked 100%)

Is there a link between the battery dying and the heater not working? Is there anything I can check to correctly diagnose the problem? Could it be as simple a blown/faulty fuse?
 
Fan 1, 2 and 3 not working sounds like a resistor issue. Could be (but only very distantly) related to the jump start, and even then I doubt it.

Only blowing cold could be a number of things. From a flap not moving as it should (although they usually fail to hot) to a heater matrix being silted up.


Oli.
 
The resistor issue is discussed here:

http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/90199-blower-motor-resistor-pack-where.html

The always-cold issue could be one of many things. First is to test to make sure that all the flaps in the heater are moving as they should, and to do that you need to stick you head under the dashboard (passenger side footwell is great) and understand what's going on. If they are then take some pipes off and see if you can stick your fingers close to the matrix, and see whether it is getting hot. Work on from there ...


Oli.
 
Check the black and blue valve that's next to the firewall behind the cam tower. It's connected to the manifold vacuum line, mine popped off and heater only blew cold.
 
Blowing cold would suggest the heater control valve which is driven by vacuum, it is either near the rear bulkhead or on later cars behind the distributor on left as you look in near cam cover. You can disconnect the pipe on the top and see if it has any vacuum and also connect up a syringe to the valve with a bit of rubber tube and suck to see if valve opens. This valve normally fails open (always hot) but it could be not getting any vac from the heater conrol unit. You can also check the pipes into and out of it to see if they are hot as it could be an airlock. Depends on the year of your car there is a good description/diagram for the heater functions on the TIPEC forum in Clarks Garage section which shows the connections and what they do.
 
could also be the heater flap servo motor - the one that is connected to the clip that breaks behind the glovebox - move the control and it should move - on my lux it had seized, I dismantled it cleaned it, ran the motor direct on a battery, it worked for years after.
Tony
 
It was the heater control valve.

Not so long ago, in my first outing in the 944 this year, the car broke down. Initially I thought one of the coolant pipes snapped but it turns out it was the heater control valve. As soon as the heater control valve was replaced, this issue disappeared.

Thanks for your replies.
 
Thanks for the update. Glad to hear it's all as it should be and it's helpful to hear how far out we were with our diagnoses (resistor pack, eh!) Top marks to David for getting it right.


Oli.
 
Unfortunately there is another update on this....

A day after confirming everything was ok, the problem returned. The difference being this time there is warm air coming out. Moving the knob to between positions off, 1, 2, 3 makes no difference re fan speed. Only position 4 works.

Any idea what would cause this?
 
Your Fan speed problem was answered in the first few replies to this post. There is a resistor pack under the plastic shroud at the front of the windscreen, it's directly above the glovebox and unplugs easily. New ones have historically been expensive but its always worth calling Porsche. I bought a S/H one from Porsch-apart about ten years ago for £20
 
Ha! I was right all along! >DoesALittleDanceOfJoy< [:D]

Especially pleasing given my mea culpa post (post #11, above.)


Oli.
 
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