Heating/Ventilation Coolant Crossover

Reply Sat 7 Apr, 2007 11:50 am
I've got a 1993 Buick LeSabre. The heaing/ventilation/AC has been misbehaving recently, mostly evidenced by an inability to redirect the desired airflow to the correct vents. Mostly right now only the defroster/windshield vent has been actually emitting ventilation.

Recenty, the defroster vents began emitting an inordinate amount of moisture when they are activated at the high fan speed. The moisture seemed to have an odd smell and filmy content that made it difficult to wipe the windshield clean. It was only then I realized it was radiator coolant.

My best guess is that there's been some sort of failure with the heater core, which even at my novice level I know acts just like a mini-radiator and allows heated coolant to be circulated through it so that the heat can be transferred into the car's interior via the fan motor.

My best hope is that some hose to the heater core has sprung a small leak and is allowing coolant to drip into the fan assembly - which is being semi-atomized and being blown up into the defroster vents. Any suggestions on an approach to try to confirm this diagnoses and maybe an on-line source to help me with a fix attempt?
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Reply Sat 7 Apr, 2007 12:08 pm
You are going to have to pressurize the coolant system and crawl around to locate the leak. Heater core access could be a pain and yes if you have properly maintained the cooling system then a hose or clamp is more likely than the core itself but if you have not maintained the coolant system then all bets are off.
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Reply Wed 23 May, 2007 12:17 am
99.99% of the time, this is the answer: coolant leak to the vents absolutely must be a bad heater core. A leaking hose would drop coolant outside the car on the ground. the only way for coolant to get inside the vent area is if the heater core were leaking.

The air ducting is usually controlled by a vacuum operated regulator. It is a round disc-type thing mounted to the heater box somewhere with a rod to a lever on one side and a vacuum hose on the other. The rubber diaphragm inside uses engine vacuum to hold a door shut which directs air to one of the destinations. When you select a position on the dash control, it simply directs vacuum to the proper place. The rubber diaphragm over time develops a crack which makes it inoperable. The result is that the doors don't move and you get all of your air from one place (usually the defroster)
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Reply Fri 27 Jul, 2007 07:13 pm
To close out this incident, I can report that after purchasing about 8 inches of narrow diameter heater hose ($1.79), and two clamps ($.89), I removed the old hose and cross-clamped the hose into a continuous loop back into the engine block - and the problem seems to have been solved.

Admittedly, the heater will no longer provide heat to the interior compartment passenger compartment. I think this confirms a faulty heater core.
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