No heat in '90 Lumina APV

I have tried everything I was able to Google up, but apparently have not gotten to the root of the issue yet. I'm hoping someone here will be able to
steer me in a fruitful direction. I have never had a problem with heat in this vehicle before, except for having to replace the heater core 3 or 4 years ago. About a month ago, I turned on the defrost to knock the fog off my windshield, and no heat. So far I have tried the following: Checked the heater core supply hose... gets real hot; checked the heat control potentiometer... seems fine; checked the vacuum lines... found a leak in the one to the blower housing, repaired with vinyl tape - actuator appears to work, as do the other two vacuum actuators. Is there anything else under the dash or in the engine bay that could prevent me from geting heat? Thanks in advance, Bruce
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Bruce Adams wrote:

Does the heater return hose get hot? Perhaps the core is plugged up.
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" Paul " <"=?x-user-defined?Q??= Paul

I will admit to an aversion to lean into the engine bay to reach across the serpentine belt while on tiptoes. :-) I will check this out. My coolant had been low, which I forgot to mention. I filled it while the engine came to temp and the heat on full. (That gets messy!) Then I parked nose-up on a 30% grade and ran it for 30 minutes to coax any possible air out of the heater core, but no joy.
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Bruce Adams wrote:

That's an excellent way to purge air from the system. There should be at least one purge valve - somewhere. There is NO valve to shut off the water flow. Car makers depend on flow through the heater for additional engine cooling. There is only the temperature door. On your vehicle it should be manual rather then electric stepping motor. OTH, there could still be air in the system.
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.> >> Bruce

Well, the damnedest thing -- yesterday as I drove home, heat just started pouring out of the thing. (I've been leaving the heat on all the time just kind of crossing my fingers.) The odd bit is that yesterday morning, when I needed to defog my windshield... nothing. And the only thing it did between morning and afternoon was sit parked. Go figure! Thanks everyone for all your suggestions, and it looks like the automotive gods looked down on me with pity for a change. Bruce
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" Paul " <"=?x-user-defined?Q??= Paul

Is there a servo motor or something that is controled by the temperature potentiometer? The thing really acts like it's set for cold even when the knob is pushed all the way to hot. Thanks, BA.
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thermostat On Wed, 21 Sep 2005 03:47:52 GMT, " Paul " <" Paul

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wrote:

Where is that thermostat? Perhaps it has failed in a fashion that reports it is too hot. Or are you talking about the engine coolant thermostat? As near as I can tell, that seems to be working. At least, the engine comes up to temp OK. Thanks, Bruce
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On Wed, 21 Sep 2005 01:07:23 GMT, "Bruce Adams"

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