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  #1  
Old 25th December 2007
eric43 eric43 is offline
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Default 84 900 heater

With the heater on, air from vents turns cool if the car is moving less than 20 mph. What's up?!
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  #2  
Old 25th December 2007
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Low coolant level can cause that sympyom.
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  #3  
Old 25th December 2007
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Fluid's between max and min in the reservoir. Maybe there's a bubble.
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Old 25th December 2007
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Quote:
Originally Posted by eric43
Fluid's between max and min in the reservoir. Maybe there's a bubble.
Could be a good idea to bleed the coolant system and see what happens as there could be some blockages or trapped air in the lines to/from the heater core or the core itself. Start the engine, set the temp knob to'hot' so the heater control valve is fully open, open the thermostat bleeder nipple a bit, and see if you get a steady stream of fluid or if it's bubbling. Should be fine though as you're driving the car around and haven't noticed any issues with the cooling system. If there's any bubbling, let it continue until the bubbling stops, and if you need to, top up the coolant tank a little.

Does the air actually go fully cold (ie. it's coming through the cabin fan, etc. completely un-heated), or does the heat drop off but not fully (ie. the air doesn't feel 'hot' but it's not actually cold)?

Have you tried the setting of the main control which bypasses the cabin fan resistor pack to get full flow of ventilation air under low-speed conditions to see if that makes a difference?

Craig.
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  #5  
Old 25th December 2007
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What is the dashboard temperature gauge's behaviour when this happens?
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  #6  
Old 28th December 2007
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I think the heating problem is ok now. I bled the system, and there were a few splutters of air, so mebbe that was the problem. Thanks!
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Old 29th December 2007
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Thats strange, I thought it was forced feed through the heater valve until the thermostat opened (which should move any air blocks). Check to see if the thermostat is jambed open? Although, maybe my car is different.
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Old 12th January 2008
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Guess I know a little more about the heater operation after several days of paying attention to it: With the engine fully warmed up, heated air from the vents will gradually cool, eventually to ambient temp, if the car is still or moving slowly. If I turn the valve to full open, the air will gradually heat up again. Anyone else have this kind of heater operation?
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Old 12th January 2008
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Quote:
Originally Posted by Matthew
What is the dashboard temperature gauge's behaviour when this happens?
Temp gauge seems to act the same, whether the heater valve is on or not: If the car is sitting still with engine idling, the water temp will gradually rise to about 3/8" from hot, then both fans will run to bring back down to about 5/8" from hot. I've never seen it higher than 3/8" from hot.
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Old 12th January 2008
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I read somewhere that there is a dual stage thermostat in the saab cars. When the coolant heats up it opens the thermostat a little to allow the water circulate through the rad. That way, it doesn't get cooled too much at once, and there is enough pressure left in the engine circuit to force the water through the heater core. Then, if the water gets even hotter, it opens fully. The thermostat isn't expensive and is easy to replace. But, make sure you get the correct one.
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Old 12th January 2008
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Hmmm, another idea; Maybe there is a very slow vacuum leak in the controls for opening and closing the flaps. The increase in engine speed would increase the vacuum. Do any of those flaps actually bypass the heater core?
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  #12  
Old 12th January 2008
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Well, I think the center vents bypass the heater core - never get any heat out of them. But I haven't been referring to them regarding this strange cooling. Anyway, I know what to do when things cool off while I'm sitting in traffic in winter. Mebbe I'll replace the thermostat - I did install a new one about a year ago, bought from the dealer.
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Old 12th January 2008
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Ya, the centre vent by passes the heater core. Ignore the vacuum bit, i think the rest of the vents have to go through the core.

After starting the engine does the heating work properly for a while, until the engine fully warms up? If yes, that indicates that the heating works ok with the thermostat closed, and the water confined to flowing through the engine and heater core only.

Is the problem only recent or was it there since you changed the thermostat? Was the heating working properly before?
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